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. 2022 Nov 10;17(11):e0276834. doi: 10.1371/journal.pone.0276834

The prevalence, incidence, and risk factors of mental health problems and mental health service use before and 9 months after the COVID-19 outbreak among the general Dutch population. A 3-wave prospective study

Peter G van der Velden 1,2,*, Miquelle Marchand 1, Marcel Das 1,3, Ruud Muffels 2, Mark Bosmans 4
Editor: Marcus Tolentino Silva5
PMCID: PMC9648763  PMID: 36355792

Abstract

Objectives

Gain insight into the effects of the COVID-19 pandemic on the prevalence, incidence, and risk factors of mental health problems among the Dutch general population and different age groups in November-December 2020, compared with the prevalence, incidence, and risk factors in the same period in 2018 and 2019. More specifically, the prevalence, incidence, and risk factors of anxiety and depression symptoms, sleep problems, fatigue, impaired functioning due to health problems, and use of medicines for sleep problems, medicines for anxiety and depression, and mental health service.

Methods

We extracted data from the Longitudinal Internet studies for the Social Sciences (LISS) panel that is based on a probability sample of the Dutch population of 16 years and older by Statistics Netherlands. We focused on three waves of the longitudinal Health module in November-December 2018 (T1), November-December 2019 (T2), and November-December 2020 (T3), and selected respondents who were 18 years and older at T1. In total, 4,064 respondents participated in all three surveys. Data were weighted using 16 demographics profiles of the Dutch adult population. The course of mental health problems was examined using generalized estimating equations (GEE) for longitudinal ordinal data and differences in incidence with logistic regression analyses. In both types of analyses, we controlled for sex, age, marital status, employment status, education level, and physical disease.

Results

Among the total study sample, no significant increase in the prevalence of anxiety and depression symptoms, sleep problems, fatigue, impaired functioning due to health problems, use of medicines for sleep problems, of medicines for anxiety and depression, and of mental health service in November-December 2020 was observed, compared with the prevalence in November-December 2018 and 2019 (T3 did not differ from T1 and T2). Among the four different age categories (18–34, 35–49, 50–64, and 65 years old and older respondents), 50–64 years respondents had a significantly lower prevalence of anxiety and depression symptoms at T3 than at T1 and T2, while the prevalence at T1 and T2 did not differ. A similar pattern among 65+ respondents was found for mental health service use. We found no indications that the incidence of examined health problems at T2 (no problems at T1, problems at T2) and T3 (no problems at T2, problems at T3) differed. Risk factors for mental health problems at T2 were mostly similar to risk factors at T3; sex and age were less/not a risk factor for sleep problems at T3 compared with at T2.

Conclusions

The prevalence, incidence, and risk factors of the examined mental health problems examined nine months after the COVID-19 outbreak appear to be very stable across the end of 2018, 2019, and 2020 among the Dutch adult population and different age categories, suggesting that the Dutch adult population in general is rather resilient given all disruptions due to this pandemic.

Introduction

The ongoing COVID-pandemic and preventive measures to contain the pandemic as much as possible have profound negative effects on affected countries and their residents. These effects vary from, but are not restricted to, higher death rates, recovery problems among infected, overloaded hospitals, closed schools, and diminished social contact, job loss, repeated lockdowns, political tensions, diminished economic growth, and large governmental financial debt. The global weekly Operational Update on COVID-19 of the World Health Organization of November 6 2020 and December 21 2020 [1], the period in which the last survey of the present study was conducted, reported 1,231,017 and 1,690061 deaths respectively and 48,534,508 and 75,704,857 confirmed COVID-19 cases respectively.

Although effective vaccines became available in 2021 [2], the question to what extent this pandemic affected the mental health of the general population is and remains important. Based on the Conservation of Resources (COR) theory of Hobfoll [3, 4] we may expect that the pandemic has negative effects among the general population since it directly or indirectly threatens important resources such as safety and health (for instance by being infected, loss of a significant other), social contacts and support (for instance by social distancing and staying-at-home following lockdowns), work and income (for instance by loss of job or reduced work) among the general population. Resource loss is an important factor, like existing problems, in predicting the impact of stressful events on mental health such as this pandemic. However, according to the COR [3, 4] people also strive to obtain, retain, protect resources, and to restore lost resources (such as social contacts, employment, housing, health) and their resilience should not be underestimated [36]. The duration of this pandemic and effects may nevertheless undermine the capacity of individuals, communities, and countries to cope with the negative effects of this pandemic on the medium and longer term. This may cause stress and increase the risk for mental health problems.

To gain insight into the effects on mental health, prospective studies based on probability samples of the general population with pre-COVID-19 data are warranted. However, compared with the large number of cross-sectional COVID-19 studies that are often based on convenience samples for which the representativeness is unclear [7, 8], the number of prospective studies based on probability samples is relatively limited. In the beginning of 2021, we identified 12 prospective peer-reviewed studies that were based on probability samples of the general population with nonretrospective data on pre-COVID-19 mental health. Below we first provide a brief summary of the main outcomes of these studies. Given the aim of the present study, we focus on the prevalence of mental health problems among the total study samples and different age categories.

With respect to the UK, the study by Pierce et al. [9] showed that mean scores on the General Health Questionnaire (GHQ-12) increased significantly from 11.5 in 2018–2019 (data were collected year-round) to 12.6 in April 2020. This increase was not considered a simple continuation of previous upwards trends from 2014 to 2019. The prevalence of clinically significant mental distress increased from 18.9% in 2018–2019 to 27.3% in April 2020. The increase in mental distress appeared to be the largest in respondents 18–34 years old. The study by Proto and Quintana-Domeque [10] showed similar findings up to April 2020 but focused especially on ethnicity and gender. Niedzwiedz et al. [11] found that the proportion of people drinking four or more times per week increased (Relative Risk (RR) = 1.4) as did binge drinking (RR = 1.5). Daly et al. [12] analyzed data on mental health up to June 2020. Their results showed that the prevalence of mental health problems increased from 24.3% in 2017–2019 to 37.8% in April, 34.7% in May, and 31.9% in June 2020. Although elevated in June 2020 compared with 2017–2019, the prevalence was lower (-5.9%) than in April 2020. Respondents of 18–34 years old showed the largest increase in the prevalence of mental health problems.

Of the prospective studies in the USA, Twenge and Joiner [13] compared anxiety and depression symptomatology among adults in the National Health Interview Survey (NHIS; January-June 2019) and the Household Pulse Survey (HPS; April-May 2020). Respondents in the HPS were three to four times more likely to screen positive for anxiety or depression disorders compared with respondents in the NHIS. McGinty et al. [14] using data of the NHIS (2018) and the Johns Hopkins COVID-19 Civic Life and Public Health Survey (April 2020), found that the prevalence of psychological distress increased from 3.9% to 13.6%, and the prevalence increased the most among young adults aged 18 to 29 years (4% to 24.0%). Daly et al. [15] used data of the National Health and Nutrition Examination Survey (NHNE, 2017–2018) and the Understanding America Study (UAS, March and April 2020). Results showed a significant higher prevalence of depression symptoms in March (10.6%) and April 2020 (14.4%) than before the outbreak (8.7%). Among 18–34 years old respondents, the increase was 7.3% between pre-COVID and March 2020, and 13.4% between March and April 2020. Among older respondents, a smaller increase between March and April 2020 was found. Breslau et al. [16] found that the prevalence of clinical psychological distress in February 2019 (10.9%) was as high as in May 2020 (10.2%). Among 20–39 and 40–59 years old respondents, the prevalence of respondents who suffered from an increase in problems (20.8% and 14.4% respectively) was higher than among those of 60 years and older. Ettman et al. [17] compared the prevalence of depression symptoms among respondents of the COVID-19 Life Stressors Impact on Mental Health and Well-being study conducted in the period March 31, 2020-April 13, 2020 and, like Daly et al. [15], and respondents of the NHNE Survey conducted in 2017–2018. Results showed that the prevalence of mild and severe symptoms was higher during COVID-19 than before (mild: 24.6% vs 16.2%, severe: 5.1% vs 0.7%). In contrast to pre-COVID-19, during the pandemic moderate to severe depression symptom levels differed between age categories with a higher prevalence among younger adults.

With respect to the Netherlands, Van der Velden et al. [18] found, like Breslau [16], no increase in the prevalence of anxiety and depression symptoms among adults in March 2020 (17.0%) compared with the prevalence in November 2019 (16.9%). Compared with 18–34 years old respondents (19.7%), 35–49 years respondents had a significant higher prevalence (22.1%) and 65 years and older respondents had a lower prevalence of symptoms (10.6%) in March 2020. The study by Van Tilburg et al. [19] focused on respondents of 65 years and older. Results showed a significant but trivial improvement in May 2020 compared with November 2019. The follow-study by Van der Velden et al. [20] with data up to June 2020, showed a significant but small decrease in the prevalence of anxiety and depression symptoms in June (15.3%) compared with March 2020 (17.2%) and November 2019 (16.8%). In addition, they found that the recovery of symptoms in the period November 2019- March 2020, did not differ significantly from the period March 2020 to June 2020.

The aforementioned studies mainly focused on psychological distress, anxiety, and depression symptoms, and did not provide insight into the effects of the COVID-19 pandemic on the prevalence of other relevant mental health problems such as fatigue and sleep problems, and other indicators of mental health such as the use of medicines for anxiety and depression symptoms, use of medicines for sleep problems, mental health service use, and impaired functioning due to health problems. Moreover, little is known about the post-COVID-outbreak incidence of mental health problems compared with the incidence of mental health problems before the COVID-19 outbreak. Finally, very little is known about the extent to which prospective risk factors of mental health problems before the outbreak are also prospective risk factors of problems and service use after the outbreak [18].

With respect to COVID-19 in the Netherlands, soon after the outbreak, the Dutch government implemented large financial support programs for companies who significantly lost revenues because of the COVID-19 pandemic to allow them to keep people employed. In addition, governmental taxes were postponed. The Dutch governmental deficit increased in 2020 with 40 billion euro to 435 billion euro largely due to these financial programs [21]. In 2020, about 800,000 residents were tested positive for COVID-19, although the number of residents with COVID-19 in 2020 is presumably higher [22]. After the outbreak, residents and companies were confronted with several (partial) lockdowns in 2020, including closed schools and universities. Statistics Netherlands (CBS) reported that about 169,000 had died in the Netherlands, 10% more than expected compared with previous years [23].

The aim of the present prospective population-based study is to fill the above identified gaps of scientific knowledge. For this purpose, data on health were extracted from surveys conducted with the LISS panel in November-December 2018 (T1), November-December 2019 (T2), and November-December 2020 (T3), nine months after the COVID-19 outbreak. It is part of an ongoing COVID-19 study [18, 20, 24] using this longitudinal panel. Research questions of the present study were:

  1. To what extent did the prevalence of mental health problems and mental health service use among the general population before the COVID-19 outbreak in November-December 2018 (T1) and 2019 (T2), differ from the prevalence after the COVID-19 outbreak in November-December 2020 (T3)?

  2. To what extent did the incidence of mental health problems and mental health service use among the general population before the COVID-19 outbreak in November-December 2019 (T2), differ from the incidence after the COVID-19 outbreak in November-December 2020 (T3)?

  3. To what extent were well-documented risk factors of mental health problems and mental health service use before the outbreak (November-December 2019, T2), comparable with risk factors of problems and service use after the outbreak (November-December 2020, T3), such as sex, age, education level, marital status, employment status and physical health [2528].

Materials and methods

Procedures and participants

For the present study, data on mental health were extracted from the Longitudinal Internet studies for the Social Sciences (LISS) panel [29]. This panel is based on a traditional probability sample drawn from the Dutch population register of 16 years and older by Statistics Netherlands and administered by Centerdata. People cannot sign up themselves as respondents for the LISS panel. The set-up was funded by the Dutch Research Council (NWO). Panel members receive an incentive of 15 euros per hour and members who do not have a computer and/or internet access are provided with the necessary equipment at home (for further information about the LISS panel, all conducted studies since 2007, and open access data see: https://www.dataarchive.lissdata.nl; in English).

Data on mental health of adults were extracted from the longitudinal Health module, in particular the waves in November 2018 (T1: Ninvited = 6,466, response = 84.4%), in November 2019 (T2: Ninvited = 5,954, response = 86.4%), and in November 2020 (T3: Ninvited = 6,832, response = 83.6%), with reminders in December of each year. In total, 4,107 respondents who were 18 years or older at T1, participated at T1, T2, and T3. The total study sample consisted of 4,064 respondents with complete data across the three surveys (99%). We next weighted the data using 16 exclusive demographic profiles among the total adult Dutch population to optimize the representativeness of the current study, based on the data of Statistics Netherlands (see: https://opendata.cbs.nl/#/CBS/en/; in English). The 16 profiles were constructed using the variables sex (male, female), age (18–34, 35–49, 50–64, 65 years and older), and marital status (married and unmarried), yielding 2*4*2 = 16 demographic profiles. All findings are based on the weighted sample.

Ethical approval and informed consent

Since our research did not impose certain (experimental) behavior, our research did not need the approval of a Dutch Medical Ethical Testing committee according to the Dutch Law (see https://english.ccmo.nl/investigators/legal-framework-for-medical-scientific-research/your-research-is-it-subject-to-the-wmo-or-not). Nevertheless, the Health module (as part of the Longitudinal Core Study in LISS, starting in 2007) was evaluated and approved by the Board of Overseers, an Internal Review Board (IRB) until 2014. In accordance with the General Data Protection Regulation (GDPR), participants gave explicit written consent for the use of the collected data for scientific and policy relevant research.

Measures

We used the following six measures administered in each survey to obtain insight into the mental health problems and mental health service use of respondents in November-December 2018, 2019, and 2020. At each survey respondents’ sex, age, marital status, and employed status (primary occupation) was assessed. For the present study, marital status and employed status were recoded into married (1 = yes, 2 = no) and employed (1 = yes, 2 = no).

Anxiety and depression symptoms

Anxiety and depression symptoms were examined using the Mental Health Index or Inventory (5-item subscale of the Medical Outcomes Study (MOS), 36-Item Short Form Survey Instrument (SF-36, [30, 31])). Respondents were asked to rate their mental health during the past month on 6-point Likert scales (0 = never to 5 = continuously). After recoding the negatively formulated items (items 1, 2, and 4), the total scores were computed and multiplied by four (range 0 to 100, all Cronbach’s α > .85). Lower scores reflect higher symptom levels. A cut-off of ≤ 59 was used to identify respondents with moderate to severe symptom levels and a cut-off of ≤ 44 to identify respondents with severe symptom levels [32].

Fatigue and sleep problems

Respondents were furthermore administered a list of 10 (physical) problems people may suffer from, varying from heart complaints to sleeping problems. For the present study, we focused on the items ‘Do you regularly suffer from fatigue’ and ‘Do you regularly suffer from sleep problems’ (1 = no, 2 = yes).

Impaired functioning due to (mental) health problems

Psychopathology is consistently and independently associated with increased disability [31]. Health-related impaired functioning were assessed with the question ‘To what extent did your physical health or emotional problems hinder your work over the past month, for instance in your job, the housekeeping, or in school? This question is comparable with questions of the MOS-36 [33] and the European Health Interview Surveys (SILC-EU) [34], and had a 5-point Likert scale (1 = not at all to 5 = very much). For the present study, the scores were recoded into low (1 = 1,2,3) and high (2 = 4,5).

Medicines for anxiety and depression

Use of medicines were assessed for several conditions varying from medicines for blood pressure to sleep problems (‘Are you currently taking medicine at least once a week for ‥ ‘). In the present study, we focused on the current use of medicines for anxiety and depression symptoms and sleep problems (0 = no, 1 = yes).

Mental health service use

Mental health service use (MHS) was assessed by one question ‘How often did you use the following health services over the past 12 months?’, with answer categories varying from psychiatrist/ psychologist/ psychotherapist to dentist. For the present study, we focused on the use of a psychiatrist, psychologist, or psychotherapist and recoded ‘use’ into ‘no’ (0 = no use) and ‘yes’ (1 = once or more) in the past 12 months.

Physical disease

Respondents were administered a list of 19 physical diseases/ problems and asked if they had one or more of these diseases/problems according to a physician (‘Has a physician told you this last year that you suffer from one of the following diseases/ problems?’) varying from cancer to chronic lung disease. For the present study, we recoded the answers into ‘no disease’ (1 = none of the diseases/problems included in ‘diseases’) and ‘disease’ (2 = angina; pain in the chest a heart attack including infarction or coronary thrombosis or another heart problem including heart failure; stroke or brain infarction or a disease affecting the blood vessels in the brain; diabetes or a too high blood sugar level; chronic lung disease such as chronic bronchitis or emphysema; asthma; arthritis, including osteoarthritis, or rheumatism, bone decalcification or osteoporosis; cancer or malignant tumor, including leukemia or lymphoma; and/or benign tumor (skin tumor, polyps, angioma)).

Statistical methods

To examine the extent to which the prevalence of the seven assessed mental health problems after the COVID-19 outbreak in November-December 2020 (T3) changed compared with the prevalence in November-December 2018 (T1) and 2019 (T2), generalized estimating equations (GEE) for longitudinal ordinal data were conducted (GENLIN in SPSS version 28, using an autoregressive working correlation structure) with problems at T1, T2 and T3 as dependent variables (separate analyses for each dependent variable). In the analyses, sex, age, marital status, employment status, education level, and disease at T1, T2, and T3 were used as control variables.

For the incidence at T3 (prevalence of new cases), the prevalence of mental health problems and use at T3 was assessed among those without these problems and or use at T2. Likewise, for the incidence at T2, problems and use at T2 were assessed among those without these problems and use at T1 (the incidence at T1 could not be computed among the current study sample). To assess the extent to which the incidence of mental health problems and use in November-December 2020 (T3) changed compared with the incidence in November-December 2019 (T2), multivariate logistic regression analyses were conducted as follows. The incidence at T2 and T3 cannot directly be compared because those with problems and use at T2 and T3 without problems and use at the previous survey partly overlap. To enable a comparison of the incidence at T2 and T3, we therefore first randomly split the total study sample into two almost equal independent subgroups of respondents (A: n = 2,025; and B: n = 2,019; because of the weighting the numbers of both groups slightly differs). In both subgroups, the incidence at T2 (A1, B1) and T3 (A2, B2) were computed. We finally compared the incidence of A1and B2, and compared the incidence of B1 and A2 using logistic regression with the same control variables (control variables at T1 for analyses incidence at T2, control variables at T2 for analyses incidence at T3).

Prospective risk factors of mental health problems and service use were examined using multivariate logistic regression analyses with problems and service use at T2 and T3 as dependent variables. The variables sex, age, education level, marital status, employment status, and physical disease at T1 and T2, respectively, were simultaneously entered as predictors (for instance, variables at T2 were entered as predictors for problems at T3).

Results

Nonresponse

Multivariate logistic regression analyses (before weighting) with nonresponse at T2 and T3 as the dependent variable (1 = participated at T1, T2 and T3, 2 = did not participate at T2 and T3) showed that the nonresponse was not significantly (p > .05) associated with the seven mental health and mental service use variables at T1, disease at T1, and not with sex, employment status, and education level at T1. Unmarried respondents (85.1%) compared with married respondents (90.4%) participated less at T1, T2, and T3 (adjusted Odds ratio (aOR) = 0.80, 95% confidence interval (95% CI) = 0.66–0.98, p = .029)). Compared with 18–34 years old respondents (79.1%), 34–50 years old (85.7%, aOR = 1.43, 95% CI = 1.10–1.87, p = .008), 50–64 years old (92.3%, aOR = 2.80, 95% CI = 2.10–3.75; p < .001), and 65 years or older respondents (90.7%, aOR = 2.10, 95% CI = 1.53–2.84, p < .001) participated significantly more often. As described, the study sample was weighted for sex, marital status, and age.

Characteristics of respondents

The characteristics of the study sample are presented in Table 1. It shows, among others, that in absolute numbers as time passes by, more respondents are married, become older, have a higher education level, as well as more often have a physical disease. At T3, the youngest respondents were 20 years old.

Table 1. Characteristics of respondents (N = 4,064).

Survey
2018 (T1) 2019 (T2) 2020 (T3)
n (%) n (%) n (%)
Employed
 • no 1854 (45.6) 1825 (44.9) 1867 (45.9)
 • yes 2210 (54.4) 2239 (55.1) 2197 (54.1)
Married
 • yes 1957 (48.2) 1972 (48.5) 1999 (49.2)
 • no 2107 (51.8) 2092 (51.5) 2065 (50.8)
Education level1
 • low 1013 (24.9) 992 (24.4) 969 (23.8)
 • medium 1466 (36.1) 1441 (35.5) 1416 (34.8)
 • high 1585 (39.0) 1631 (40.1) 1679 (41.3)
Sex
 • male 2002 (49.3) idem idem
 • female 2062 (50.7) idem idem
Physical disease
 • no 3303 (81.3) 3266 (80.4) 3253 (80.0)
 • yes 761 (18.7) 798 (19.6) 811 (20.0)
Age category
 • 18–34 years old 1083 (26.6) 1018 (25.0) 933 (23.0)
 • 35–49 years old 961 (23.6) 933 (23.0) 941 (23.2)
 • 50–64 years old 1052 (25.9) 1061 (26.1) 1054 (25.9)
 • 65 years old or older 968 (23.8) 1052 (25.9) 1136 (28.0)

1 Low = primary school, intermediate secondary education, US: junior high school; Medium = higher secondary education/preparatory university education, US: senior high school, intermediate vocational education, US: junior college; High = higher vocational education, US: college, 6 university according to education level categories of Statistics Netherlands (CBS). All results are based on the weighted sample. Due to weighting, numbers may slightly differ between tables.

Prevalence of mental health problems and service use of total study sample

The prevalence of the assessed mental health problems and service use among the total study sample at T1, T2, and T3 are presented in Table 2. The prevalence of mental health problems and service use at T3 did not significantly differ from T1 and T2 except for impaired functioning due to health problems. The prevalence of impaired functioning due to health problems was significantly lower at T3 (8.5%) than at T1 (9.9%), but not significantly different from the prevalence at T2 (8.5%).

Table 2. Prevalence of mental health problems and service use (N = 4,064).

November-December 2018 (T1) November-December 2019 (T2) November-December 2020 (T3) T1 versus T3 T2 versus T3 T1 versus T2
Prevalence n (%) n (%) n (%) aOR (95% CI) aOR (95% CI) aOR (95% CI)
Anxiety and depression symptoms1 660 (16.2) 687 (16.9) 686 (16.9) 1.09 (0.99–1.19) 1.00 (0.92–1.09) 1.08 (0.99–1.18)
Sleep problems 834 (20.5) 871 (21.4) 869 (21.4) 1.03 (0.98–1.09) 0.99 (0.95–1.03) 1.05 (1.00–1.09)*
Fatigue 1275 (31.3) 1292 (31.8) 1266 (31.2) 1.00 (0.96–1.05) 0.98 (0.95–1.01) 1.02 (0.99–1.06)
Impaired functioning due to health problems 404 (9.9) 345 (8.5) 348 (8.6) 0.86 (0.76–0.97)* 1.03 (0.90–1.17) 0.84 (0.74–0.95)**
Medicines for anxiety/depression 190 (4.7) 187 (4.6) 195 (4.8) 1.04 (0.96–1.13) 1.04 (0.98–1.11) 1.00 (0.94–1.06)
Medicines for sleep problems 189 (4.6) 203 (5.0) 207 (5.1) 1.05 (0.94–1.17) 1.00 (0.91–1.09) 1.05 (0.96–1.15)
Mental health service use2 341 (8.4) 345 (8.5) 317 (7.8) 0.95 (0.83–1.09) 0.92 (0.82–1.04) 1.03 (0.91–1.16)

1According cut-off score of ≤ 59. 2Psychiatrist/psychologist/psychotherapist in past 12 months. aOR = Odds ratio adjusted for sex, age, marital status, employment status, education level, and disease at T1, T2, and T3. 95% CI = 95% confidence interval for aOR. All results are based on the weighted sample. Due to weighting, numbers may slightly differ between tables.

* p < .05,

** p < .01

Analyses for anxiety and depression scores using the cut-off score of ≤ 44 of the MHI-5 showed similar outcomes: the prevalence of severe symptom levels at T1 (6.6%), T2 (6.5%) and T3 (6.3%) also did not differ significantly (results not shown in table).

Prevalence of mental health problems and service use among age categories

Among respondents 18–34 years old, the prevalence of anxiety symptoms at T3 (22.3%) was significantly higher than at T1 ((19.9%, adjusted Odds Ratio (aOR) = 1.30, 95% Confidence interval (95% CI) = 1.08–1.57, p = .009)), but not compared with T2 (20.7%). In contrast, among respondents 50–64 years old, the prevalence of these symptoms at T3 (13.3%) was significantly lower than at T1 (14.6%, aOR = 0.82, 95% CI = 0.68–0.99, p = .043) and T2 (15.1%; aOR = 0.81, 95% CI = 0.68–0.95, p = .013).

With respect to sleep problems, among respondents 18–34 years old, the prevalence at T3 (14.6%) was significantly higher than at T1 (13.2%; aOR = 1.19, 95% CI = 1.02–1.39, p = .023), but not compared with T2 (14.8%).

For fatigue, no significant changes in the prevalence were found between T1, T2 and T3 across the four age categories. Only among respondents 50–64 years old, the prevalence of impaired functioning due to health problems differed significantly to some extent: the prevalence was lower at T3 (10.6%) compared with T1 (12.2; aOR = 0.78, 95% CI = 0.62–0.99, p = .039, but not compared with T2 (10.0%).

The use of medicine for anxiety and depression among respondents 18–34 years old was significantly more prevalent at T3 (3.4%) than at T2 (2.9%; aOR = 1.21, 95% CI = 1.01–1.46, p = .040) but not at T1. Concerning the use of medicines for sleep problems, no significant changes in the prevalence were found between T1, T2, and T3 across the four age categories.

Finally, the use of mental health professionals among respondents 65 years old and older decreased significantly in the 12 months before T3 (2.2%) compared with T1 (3.5%; aOR = 0.60, 95% CI = 0.41–0.87, p = .006) and T2 (3.1%; aOR = 0.69, 95% CI = 0.49–0.97, p = .031). No significant differences were found between T1 and T2 (for details see S1 Appendix Age categories).

Incidence of mental health problems and service use of total study sample

Table 3 shows the incidence of mental health problems and service use at T2 and T3 among the total study sample and the results of crosswise multivariate logistic regression analyses (A1 incidence versus B2 incidence, and B1 incidence versus A2 incidence) showing that the incidence of mental health problems and service use at T2 and T3 did not differ significantly. Similar analyses using the cut-off ≤ 44 of the MHI-5, showed that the incidence of severe anxiety and depression symptom levels at T2 (3.7%) and T3 (3.3%) also did not significantly differ (results not shown in table).

Table 3. Incidence of mental health problems and service use (N = 4,064).

November-December 2018 (T1) November-December 2019 (T2) November-December 2020 (T3) A1 versus B2 B1 versus A2
Incidence 1 n (%) n (%) n (%) aOR (95% CI) aOR (95% CI)
Anxiety and depression symptoms2 n.a. 293 (8.6) 274 (8.1) 1.00 (0.78–1.29) 0.95 (0.75–1.22)
Sleep problems n.a. 120 (3.7) 93 (2.9) 0.86 (0.59–1.25) 0.71 (0.47–1.07)
Fatigue n.a. 112 (4.0) 93 (3.4) 0.79 (0.53–1.19) 0.87 (0.59–1.28)
Impaired functioning due to health problems n.a. 173 (4.7) 205 (5.5) 1.34 (1.00–1.80) 1.06 (0.78–1.42)
Medicines for anxiety/depression n.a. 14 (0.4) 20 (0.5) 1.63 (0.56–4.77) 1.31 (0.54–3.20)
Medicines for sleep problems n.a. 38 (1.0) 36 (0.9) 1.19 (0.64–2.21) 0.76 (0.38–1.54)
Mental health service use n.a. 158 (4.2) 136 (3.7) 0.99 (0.72–1.38) 0.77 (0.55–1.09)

1Prevalence mental health problems among those without problems /use on previous survey.

2According to cut-off score of ≤ 59 of the MHI-5.

3Psychiatrist/psychologist/psychotherapist in past 12 months. n.a. = not available because 2017 survey was outside aim of this study. aOR = Odds ratio adjusted for sex, age, marital status, employment status, education level and disease at T1 and T2, and T2 and T3. 95% CI = 95% confidence interval for aOR. A1 = incidence T2 of subgroup A. B1 = incidence T2 of subgroup B. A2 = incidence T3 of subgroup A. B2 = incidence T3 of subgroup B. All results are based on the weighted sample. Due to weighting numbers may slightly differ between tables.

Incidence of mental health problems among age categories

Due to the cell counts of the incidence of mental health problems and service use at T2 and T3 (see Table 3) we limited the (cross-wise) multivariate logistic regression analyses among the four age categories to the incidence of anxiety and depression symptoms. The events-per-variable (EPV) ratio for the other dependent variables, with seven predictors including control variables, became lower than 10. The results of these analyses showed no significant differences in incidence between T2 and T3 among 18–34 years old respondents (T2incidence = 12.4%, T3incidence = 13.1%), 35–49 years old respondents (T2incidence = 9.9%, T3incidence = 9.7%), 50–64 years old respondents (T2incidence = 6.2%, T3incidence = 5.0%), and 65 years and older respondents (T2incidence = 6.1%, T3incidence = 4.8%). Using the cut-off ≤ 44 of the MHI-5 also did not reveal significant differences between the T2 and T3 incidence (results not shown in table).

Risk factors of mental health problems and service use

In Table 4, the results of the multivariate logistic regression analyses are presented (for 95% confidence intervals of the adjusted OR’s, see S2 Appendix Risk factors). Table 4 shows that existing mental health problems and service use (e.g., assessed one year earlier) were by far the strongest predictors for problems and use before and after the COVID-19 outbreak. For example, about 90% of the respondents with existing sleep problems and fatigue at T1 and T2, had sleep problems and fatigue at T2 and T3, respectively. With respect to anxiety and depression symptoms at T2 and T3, almost the same predictors were significant for these symptoms at T2 and T3: only those with a medium education level were no longer less at risk of symptoms than those with a relatively low education level. An almost similar pattern can be observed for sleep problems, only males and females did no longer differ in sleep problems after the outbreak (T3). However, 35–49 years old respondents were more at risk of sleep problems after the outbreak (at T3), but not before (at T2) relative to 65+ respondents. The patterns of risk factors of fatigue at T2 and T3 are identical. For impaired functioning due to health problems, e.g., that physical health or emotional problems hinder respondents’ work over the past month, for instance, in their job, housekeeping, or in school, the results show that significant differences between subgroups disappeared after the outbreak: those with a medium and high education level compared with those with a relative low level, males compared with females, and youngest adult group (18–34 years) compared with 65+ respondents no longer differed in impaired functioning due to health problems. Finally, for mental health service use those employed before the outbreak (T2) used services significantly less often after the outbreak (T3) than unemployed, in contrast to the period before the outbreak (T1-T2). Because of the relative low prevalence of medicines for anxiety/depression and medicines for sleep problems, we have omitted these dependent variables from the analyses.

Table 4. Risk factors of mental health problems and service use (N = 4,064).

Predictors previous year Anxiety and depression symptoms1 Sleep problems Fatigue
2019 (T2) 2020 (T3) 2019 (T2) 2020 (T3) 2019 (T2) 2020 (T3)
n (%) aOR n (%) aOR n (%) aOR n (%) aOR n (%) aOR n (%) aOR
Employed
 • no (ref.) 378 (20.4) 1 349 (19.1) 1 499 (26.9) 1 487 (26.7) 1 660 (35.6) 1 639 (35.0) 1
 • yes 309 (14.0) 0.59*** 337 (15.1) 0.76* 372 (16.8) 0.86 382 (17.1) 0.76 632 (28.6) 0.76 628 (28.0) 0.87
Married
 • yes (ref.) 262 (13.4) 1 251 (12.7) 1 406 (20.7) 1 398 (20.2) 1 572 (29.2) 1 550 (27.9) 1
 • no 425 (20.2) 1.35** 435 (20.8) 1.27* 466 (22.1) 0.99 471 (22.5) 1.14 720 (34.2) 1.11 717 (34.3) 1.26
Education level
 • low (ref.) 217 (21.4) 1 203 (20.5) 1 286 (28.2) 1 274 (27.6) 1 337 (33.2) 1 330 (33.3) 1
 • medium 247 (16.8) 0.74* 255 (17.7) 0.79 311 (21.2) 0.83 303 (21.0) 0.97 499 (34.0) 0.89 479 (33.2) 0.97
 • high 223 (14.1) 0.76* 228 (14.0) 0.67** 274 (17.3) 0.83 292 (17.9) 1.09 456 (28.8) 0.88 457 (28.0) 0.73
Sex
 • male (ref.) 294 (14.7) 1 319 (15.9) 1 314 (15.7) 1 316 (15.8) 1 495 (24.7) 1 495 (24.7) 1
 • female 393 (19.1) 1.18 367 (17.8) 0.93 557 (27.0) 1.48** 553 (26.8) 1.29 797 (38.7) 1.17 771 (37.4) 1.07
Physical disease
 • no (ref.) 503 (15.2) 1 501 (15.3) 1 582 (17.6) 1 558 (17.1) 1 901 (27.3) 1 859 (26.3) 1
 • yes 184 (24.2) 1.51** 184 (23.1) 1.76*** 289 (38.0) 1.66** 310 (38.9) 2.14*** 391 (51.4) 1.76** 407 (51.0) 1.93***
Age category
 • 65+ (ref.) 117 (12.1) 1 110 (10.5) 1 237 (24.5) 1 250 (23.8) 1 283 (29.2) 1 302 (28.7) 1
 • 50–64 years 159 (15.1) 1.77*** 148 (13.9) 1.73** 290 (27.5) 1.79* 291 (27.4) 1.64* 344 (32.7) 1.18 346 (32.6) 1.38
 • 35–49 years 187 (19.5) 2.58*** 199 (21.3) 3.25*** 185 (19.3) 1.30 186 (19.9) 1.72* 314 (32.7) 1.17 296 (31.7) 1.43
 • 18–34 years 224 (20.7) 2.26*** 229 (22.5) 3.19*** 160 (14.8) 1.35 142 (13.9) 1.10 352 (32.5) 1.50 323 (31.7) 1.46
Mental health problems/service use
 • no (ref.) 293 (8.6) 1 274 (8.1) 1 120 (3.7) 1 93 (2.9) 1 112 (4.0) 1 93 (3.4) 1
 • yes 394 (59.8) 13.36*** 412 (60.0) 14.31*** 776 (89.1) 214.07*** 776 (89.1) 243.4*** 1174 (90.8) 276.4*** 1174 (90.8) 263.68***
Impaired functioning due to health problems Mental health service use2
Predictors previous year 2019 (T1) 2020 (T3) 2019 (T2) 2020 (T3)
n (%) aOR n (%) aOR n (%) aOR n (%) aOR
Employed
 • no (Ref.) 216 (11.7) 1 214 (11.7) 1 160 (8.6) 1 165 (9.0) 1
 • yes 129 (5.8) 0.60** 134 (6.0) 0.54*** 185 (8.4) 0.82 152 (6.8) 0.46***
Married
 • yes (ref.) 160 (8.2) 1 164 (8.3) 1 135 (6.9) 1 119 (6.0) 1
 • no 185 (8.8) 1.01 184 (8.8) 1.05 210 (10.0) 1.02 198 (9.5) 1.11
Education level
 • low 122 (12.0) 1 104 (10.5) 1 79 (7.8) 1 67 (6.8) 1
 • medium 116 (7.9) 0.60** 135 (9.4) 1.16 122 (8.3) 0.81 122 (8.5) 1.09
 • high 107 (6.8) 0.69* 110 (6.7) 0.99 144 (9.1) 0.98 128 (7.8) 1.18
Sex
 • male (ref.) 120 (6.0) 1 140 (7.0) 1 121 (6.0) 1 106 (5.3) 1
 • female 225 (10.9) 1.54** 209 (10.1) 1.14 224 (10.9) 1.59** 211 (10.2) 1.62**
Physical disease
 • no (ref.) 204 (6.2) 1 203 (6.2) 1 262 (7.9) 1 235 (7.2) 1
 • yes 141 (18.5) 2.32*** 145 (18.2) 2.28*** 83 (10.9) 1.52* 82 (10.3) 1.63**
Age category
 • 65+ (ref.) 74 (7.6) 1 87 (8.3) 1 30 (3.1) 1 24 (2.3) 1
 • 50–64 years 105 (10.0) 1.95** 114 (10.8) 1.95*** 86 (8.2) 2.91*** 77 (7.3) 4.13***
 • 35–49 years 86 (9.0) 2.51*** 80 (8.6) 2.02** 100 (10.4) 3.67*** 104 (11.1) 7.52***
 • 18–34 years 80 (7.4) 2.00** 67 (6.6) 1.40 129 (11.9) 4.01*** 112 (11.0) 5.77***
Mental health problems/service use2
 • no (ref.) 173 (4.7) 1 136 (3.7) 1 158 (4.2) 1 136 (3.7) 1
 • yes 181 (52.5) 10.99*** 181 (52.5) 8.78*** 181 (52.5) 22.53*** 181 (52.5) 21.98***

1According cut-off score of ≤ 59 on MHI-5.

2Psychiatrist/psychologist/psychotherapist in past 12 months. aOR = Odds ratio logistic regression analyses, adjusted for all other variables is table assessed at the same year. 95% CI = 95% confidence interval for aOR. ref. = Reference category. All results are based on the weighted sample. Due to weighting numbers may slightly differ between tables.

* p < .05,

** p < .01,

*** p < .001

Discussion

The aims of the present prospective population-based study were to examine the prevalence, incidence, and risk factors for mental health problems and mental health service use among the adult general population 9 months after the COVID-19 outbreak, compared with before the outbreak (November-December 2018 and 2019). To optimize the representativeness of the study sample (N = 4,064), data were weighted using 16 demographic profiles of the adult Dutch population.

The main conclusion that can be drawn from the present study is that the prevalence, incidence, as well as risk factors of the assessed mental health problems and service use appear to be very stable among the general population (cf. [35]). We found no indications that on population level, the prevalence or incidence of anxiety and depression symptoms, sleep problems, fatigue, impaired functioning due to health problems, use of medicines for sleep problems, anxiety and depression, and mental health service use increased in November-December 2020, compared with pre-COVID-19 mental health and service use in November-December 2018 and in 2019. Results showed a small significant decrease in the prevalence of anxiety and depression symptoms at T3 (13.3%) compared with T1 (14.6%) and T2 (15.1%), and a small significant decrease in the mental health service use at T3 (2.2%) compare to T1 (3.5%) and T2 (3.1%). Based on the results of previous COVID-19 studies, we also examined the prevalence among 18–34 years, 35–49 years, 50–64 years, and 65 years and older respondents separately, showing almost identical results. Results did not show differences between mental health problems and mental health service use at T1 and T2 on the one side, and problems and use at T3 on the other side, except among 50–64 years old respondents and among 65+ old respondents. Our results about mental health problems seem to differ from almost all identified COVID-19 studies in the UK and US, but these studies focused on mental health problems until the summer of 2020.

Importantly, in our previous study [20], assessing anxiety and depression symptoms until the summer of 2020 (June), like the study of Breslau et al. [16] and Hyland et al. [36] no increase in prevalence compared with November-December 2019 was observed. Van Tilburg et al. [19] reported a similar finding among older respondents. As described, in the study of Breslau et al. [16] also no differences between the past-month prevalence of serious psychological distress in May 2020 and past-year prevalence assessed in February 2019 were found. In addition, they [16] found an incidence of 3.2% of serious distress according to K6. Although we used the MHI-5, this seems close to our incidence number for severe anxiety and depression symptom levels at T2 (3.7%) and T3 (3.3%). The extent to which the incidence of mental health problems after the COVID-19 outbreak in the UK and USA differed from the incidence before the outbreak is unknown. Nevertheless, in our previous study [18] we found no indications that the recovery of symptoms after the outbreak differed from the recovery before the outbreak. A recent report by Statistics Netherlands [46] showed that in the period July 2020-September 2020, 83% of the Dutch residents were positive about their general health, compared with 79–80% in the same period in 2017, 2018 and 2019.

In our study we focused on the mental health effects of this pandemic at the end of 2020, nine months after the outbreak. The identified studies with pre-COVID-19 outbreak data on mental health (see Introduction) were aimed at the mental health effects during the first months after the outbreak. This differences in study period may be of relevance. The meta-analysis by Robinson et al. [37] of peer-reviewed and all other non-peer reviewed population-based studies (until January 11, 2011) with pre-COVID-19 data found that “There was a small increase in mental health symptoms soon after the outbreak of the COVID-19 pandemic that decreased and was comparable to pre-pandemic levels by mid-2020 among most population sub-groups and symptom types”. In the recent post-outbreak USA population-based study by Riehm et al. [38] a similar pattern was found: “by August 1, the odds of mental distress had returned to levels comparable to March 11.”

We are not aware of prospective population-based COVID-19 studies to compare our findings on sleep problems, fatigue, use of pharmaceuticals, and mental health service use to. For example, sleep problems were assessed in many studies [3941], but all studies used cross-sectional study designs and many were based on convenience samples.

How can we, given the outcomes of several studies showing an increase in mental health problems [917], understand the contradicting results of the present study [20, 42]?

Several elements, other than the resilience of people [35], may play a role and may help explain these differences, but future empirical research is required to examine and test these elements and explanations. First, unemployment might be a cause for increases in mental health problems [43] but unemployment remained relatively stable in the Netherlands during the COVID 19 outbreak, whereas they increased strongly in the USA in March and April 2020. However, also in the UK the unemployment figures did not rise as dramatically as in the USA in the first two months after the outbreak. From May 2020 on, due to the COVID-19 recovery programs put in place, the employment figures declined again strongly in the USA whereas they remained stable in the UK and the Netherlands [44]. Hence, the unemployment incidence might explain some of the differences with the USA, but they cannot explain the differences with the UK findings.

Analyses of the UK Household Longitudinal Study data showed an increase until the summer of 2020 in contrast to the Netherlands [20]. Another possible explanation could be that the Brexit process and the final end of the UK membership of the EU in 2020, similar to the USA due to the presidential elections, strongly divided the country, resulting in societal tensions and uncertainties about the future outside the EU. These tensions and uncertainties may have caused stress and therefore may have increased the risk of mental health problems [4547]. With respect to the political climate, other than in the USA where the COVID-19 pandemic became part of an intense political debate and elections, to date this pandemic did not result in a similar political discourse in the Netherlands as in the USA.

Furthermore, mental disorders were much more prevalent in the USA than in the Netherlands, which may increase the risk for higher post-outbreak mental health problems [48]. It might be that the Dutch welfare and mental health care system provided better support to people with mental health issues during the COVID-19 outbreak or to people who experienced mental health issues after the outbreak than the USA or UK welfare system and mental health care system does. Unemployed adults (or adults who lost their jobs due to this pandemic) can invoke for unemployment benefits and, in principle, each Dutch citizen has health care insurance regardless of being employed or not in contrast to for example the USA.

Finally, we used other questionnaires to examine mental health than the UK and USA studies did (for instance, we used the MHI-5 and not the GHQ-12 as in the UK and K6 as in the USA studies). It is unknown if our study would have yielded other results, specifically a strong increase in mental health problems after the COVID-19 outbreak, when we had administered the GHQ-12 or K6 instead of the MHI-5. However, given the high correlations between such mental health measures [49] we do not consider that very likely.

The role of pre-COVID mental health and stressors

The absence of an increase of mental health problems between T1 and T2 on the one side and T3 on the other side does not indicate that the COVID-19 outbreak has not negatively affected the mental health of individuals. As shown by the incidence rates, a minority suffers from mental health problems not experienced one year earlier that may be partly related to the disruptive effects of the COVID-19 pandemic. In addition, besides this pandemic, on a yearly basis, about 40% of adults were confronted with potentially traumatic and life-events that increase the risk for mental health problems among those confronted with these events [50, 51]. There are no valid reasons to assume that those events put mental health less at risk because of this COVID-19 pandemic. The stress sensitization model even suggests the opposite [52]. In other words, without ignoring the disruptive effects of this pandemic, we should be aware this pandemic does not occur in a vacuum. The very strong predictive values of pre-existing mental health problems clearly demonstrate, as in the study by Breslau et al. [16], this aspect. Perhaps this pandemic partly reveals mental health problems and patterns of mental health problems that were already present before the pandemic but, because of the large (media and scientific) attention towards the mental health effects [7, 53], have become more visible because of the pandemic. An increased visibility of mental health problems should not be confused with an (strong) increased prevalence of mental health problems. In either way, this underlines the relevance of nonretrospective pre-COVID mental health assessment among post-COVID-19 population-based probability study samples.

Strengths and limitations

Although our results showed very clear patterns, some limitations need to be discussed when interpreting and using the outcomes of this study. We did not conduct clinical interviews that would certainly have enriched our study. Although our results do not point in the direction of a strong post-COVID-19 outbreak increase of mental disorders, future studies using clinical interviews will provide further insight into this topic. We extended previous prospective COVID-19 studies by assessing sleep problems, fatigue, use of medicines for sleep problems, anxiety and depression, impaired functioning due to health problems, and mental health service use. As described, sleep problems, fatigue and impaired functioning were assessed by one item questions. Future research is needed to examine the course of different aspects of sleep problems, fatigue and impaired functioning. In addition, future studies focusing on other mental health problems such as eating disorders, panic attacks, phobias, alcohol and drug misuse, and low self-esteem are warranted. The three surveys had a one-year time interval. Although we examined anxiety and depression symptoms in March 2019, March 2020, and June 2020 in previous studies, we cannot rule out the possibility that significant increases and decreases can be observed using shorter time intervals. The last survey in the present study was conducted in November-December 2020. It is unclear to what extent the results can be generalized to other developed countries who were hit harder by the COVID-19 pandemic. Finally, this study focused on adults and did not include children and adolescents who might be affected differently. At T3, the youngest respondent was 20 years old. Nevertheless, the prospective study design, the use of a large population-based probability sample, high response rates, that the nonresponse was not related to our dependent variables, and the weighting of data using 16 demographic profiles of the Dutch population are major strengths of the present study.

Final conclusions

An important lesson that can be drawn from all prospective studies to date is that the large majority of the general population in general was capable, even though this pandemic disrupted many aspects of life, to preserve their mental health during 2020. Similar to before the outbreak, a small part of the general population developed mental health problems during the pandemic that were not present before. Interestingly, the study by Pan et al. [54] showed that among people with depressive, anxiety, or obsessive-compulsive disorders, symptoms did not increase during the first months after the outbreak (cf. [20]). We offered possible explanations for the differences in results between the studies in the UK and USA on the one hand and the Netherlands on the other hand. Future comparative multi-country studies, including middle and low-income countries, are needed to further disentangle the complex relationships between especially existing welfare and health care systems, the size and dosage of governmental financial support programs, political systems and tensions, preventive measures, and mental health among the general population. Ongoing monitoring of the mental health of the general population is needed because the duration of this pandemic may undermine the capacity of individuals to cope with the consequences on the longer term.

Supporting information

S1 Appendix. Age categories.

(DOCX)

S2 Appendix. Risk factors.

(DOCX)

Data Availability

The study was conducted using the Dutch Longitudinal Internet studies for the Social Sciences (LISS) pane. The LISS panel started in 2007 and is based on a large traditional probability sample drawn from the Dutch population. The Dutch Research Counsel (NWO) funded the set-up of LISS. Panel members receive an incentive of €15 per hour for their participation and those who do not have a computer and/or Internet access are provided with the necessary equipment at home. Further information about all conducted surveys and regulations for free access to the data can be found at https://www.dataarchive.lissdata.nl/ (in English). The LISS panel has received the international Data Seal of Approval (see https://www.datasealofapproval.org/en/). All data of studies conducted with the LISS panel are anonymized.

Funding Statement

The author(s) received no specific funding for this work.

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Decision Letter 0

Fuschia M Sirois

5 Jun 2021

PONE-D-21-04880

The prevalence, incidence and risk factors of mental health problems and mental health services use before and 9 months after the COVID-19 outbreak among the general Dutch population. A 3-wave prospective study.

PLOS ONE

Dear Dr. van der Velden,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Both reviewers found the topic of the research to be important and timely. They also agreed that the use of a large population-based longitudinal data set was a clear strength of the study. However, both reviewers raised some concerns about the lack of theoretical clarity for the rationale of the research, and noted that the rationale and findings could be better positioned within relevant social, epidemiological, and political contexts. Doing so would allow for more meaningful comparisons between the Dutch population and other relevant populations. These and other thoughtful comments from the reviewers should be given full and careful consideration in your revision.

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Kind regards,

Fuschia M. Sirois, PhD

Academic Editor

PLOS ONE

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Reviewer #1: Partly

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: I read this paper a few times, because as a reader I felt its presentation was confusing and I wanted to make sure I had not missed the point. For example, the introduction has sections delineated as ‘results’ which come before the methods section. I was unsure what these ‘results’ meant and why they came before the methods section. The research design was also unclear with different designs alluded to ranging from repeated measures in the abstract to prospective in the introduction, if it was a repeated measures prospective study it would have been clearer to use the same terminology throughout for consistency. There is clarity in the well-performed statistical analysis, but the rationale for the focus on mental health, sleep and medication use was unclear.

I found the statement confusing about the lack of studies on sleep and COVID -19, because there are numerous studies on sleep and the relationship with COVID-19 including some longitudinal and some systematic reviews. Given how multi-factorial mental health is and the unique situation presented by the global pandemic, I wondered about the utility and how the interpretation of results could be used to positive effect within the field of mental health. I was also unsure as to the validity of an accurate comparison with the USA and UK when the measures differed between all the studies mentioned. Furthermore, in The Netherlands some questions failed to use validated measures, merely singular questions that were ‘similar’ to questions taken from validated measures.

Within the discussion, specifically pages 30-31, rhetorical reasoning appears, for example, suggesting Brexit as a reason for higher UK scores, or societal tensions dividing the UK and USA, or even COVID-19 and the surrounding political discourse. Unfortunately, there is no scientific evidence presented for these claims, which I felt weakened the paper. Furthermore, suggesting support in health systems as a potential reason for differences in results is problematic when services are structured and funded differently. This again fails to address the complexity. Considering these claims overall left the discussion feeling somewhat unfocused, as if unsure of the story it wanted to tell. On arriving at the end of the paper, as a reader I wondered about originality and addition to the evidence base because of the previous papers using the same data set from the LISS panel and suggesting similar findings.

Reviewer #2: This study examined the effects of COVID-19 pandemic on a comprehensive set of well-being outcomes including anxiety and depressive symptoms, sleep problems, fatigue, disabilities due to health problems, use of medicine for anxiety and depression, and mental health. Data were from the Longitudinal Internet studies for the Social Sciences (LISS) (N=4,064). This analysis is an extension to earlier covid related work using LISS investigating a longer time period and additional well-being outcome. Somewhat surprisingly, the authors found not significant increase in any of these outcomes. The authors conclude Dutch adults are resilient.

While the study was well done, there are still some issues that need to be addressed:

1. It would be useful to provide more depth on the social, political, and epidemiological context in the Netherlands to provide more of a global perspective. Some of this is mention in the Discussion, but elaboration in the Introduction to "set the stage" would be most useful.

- For example, how wide spread was testing? Mitigation efforts? Government response? Public opinion?

2. The authors speculate a bit for *why* there were no differences, yet other comparative countries, on balance, report lower well-being during pandemic. The reasons provided are not very well developed and need more fleshing out. This is a limitation in the paper.

3. Finally, what can the international community learn from the Dutch experience?

4. Another major limitation is there is not theoretical development in the Introduction of the paper. The authors briefly mention "conservation of resources" ... but how does that operate? Provided a theoretical framework will help with rationale for analytic approach, interpretation of results and providing additional substantive meaning.

A few other, more minor, and editorial issues:

a. Typo on pg 16. The authors mention NS for non-response, yet writ "p<.05"

b. It would also be useful to know N with all 3 T, just 2, just T1 and T3 etc.

c. Internet surveys have notorious low response rates. How was the sample chosen? What makes it representative of the Dutch population? These issues weren't spelled out in the Methods.

d. The first paragraph of the Discussion simply repeats the aims; this needs reworking.

**********

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Reviewer #1: No

Reviewer #2: No

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PLoS One. 2022 Nov 10;17(11):e0276834. doi: 10.1371/journal.pone.0276834.r002

Author response to Decision Letter 0


15 Jun 2021

Fuschia M. Sirois, PhD

Academic Editor

PLOS ONE

Dear Dr. Sirois,

Thank you very much for reviewing our manuscript and the opportunity to revise our manuscript according to the clear and helpful comments of the two reviewers.

We believe that we were able to address all 18 comments of the reviewers and that the comments helped us to improve our manuscript. We tried to better clarify the rationale and contexts of our study as much as possible by revising specific paragraphs and by adding new paragraphs.

Below we have described in detail how we responded to each comment. We have marked the revisions in yellow in the revised manuscript and we hope that this revised manuscript meets your criteria.

Kind regards, also on behalf of my co-authors,

Peter G. van der Velden

Corresponding author

REVIEWER 1

1. I read this paper a few times, because as a reader I felt its presentation was confusing and I wanted to make sure I had not missed the point. For example, the introduction has sections delineated as ‘results’ which come before the methods section. I was unsure what these ‘results’ meant and why they came before the methods section.

Response:

We regret that the headings caused confusion. The three “results” sections in the introduction were about the results of published prospective studies in different countries and not about the results of our present study.

Following this comment, we therefore added a new subheading to better clarify for the reader that these sections provide an overview of the results of previous prospective studies on the mental health of the general population:

Results of previous prospective COVID-19 studies on the mental health of the general population (corps 16).

Being aware that (almost) accepted but not published peer-reviewed studies are missed, to date we identified 12 studies (written in English) among the general population in the United Kingdom (UK), United States of America (USA) and the Netherlands that were based on probability samples of the general population with non-retrospective data on pre-COVID-19 mental health. Below we first provide a summary of the main outcomes of these studies. Given the aim of the present study (see below), we focus on the prevalence of mental health problems among the total study samples and different age categories.

Based on this comment we also revised the subheading of the sections devoted to the results in different countries (was corps 16, now corps 14):

Results of prospective studies in the UK

Results of prospective studies in the USA

Results of prospective studies in the Netherlands

2. The research design was also unclear with different designs alluded to ranging from repeated measures in the abstract to prospective in the introduction, if it was a repeated measures prospective study it would have been clearer to use the same terminology throughout for consistency.

Response

We fully agree with the reviewer that consistency in terms is very important. Based on this comment we have checked our manuscript to certify that we use the same terms throughout the manuscript. We used the description “Longitudinal Internet studies for the Social Sciences (LISS) panel” for the present study. Although we agree with the need for consistency, we cannot of course change the name of this panel and replace longitudinal with prospective.

The terms “prospective” and “repeated measures”, as for example used in the abstract, refer to two different aspects, e.g. the study design and statistical analyses and are therefore not inconsistent. Our study has “a prospective study design”. The analyses we conducted are “repeated measures multivariate logistic regression analyses”, but perhaps the reviewers meant something else.

3. There is clarity in the well-performed statistical analysis, but the rationale for the focus on mental health, sleep and medication use was unclear.

Response:

We are glad to notice that the reviewer considers our statistical analyses clear and well-performed.

We have revised the section on the Conservation of Resources theory to clarify better the rationale for our study. We would also like to refer to our response to comment 14. We believe that this revision, in combination with the other paragraphs of the introduction including the overview of population based studies on mental health problems before and after this pandemic, provides a clear rationale for the focus on mental health (including sleep and use).

4. I found the statement confusing about the lack of studies on sleep and COVID -19, because there are numerous studies on sleep and the relationship with COVID-19 including some longitudinal and some systematic reviews.

Response:

When submitting our manuscript, none of the identified prospective studies among the general population with pre-COVID data assessed differences in sleep problems before and after the COVID-19 outbreak. We are aware of the study with pre-COVID data on sleep by Evans (2021), but this study was conducted among UK university undergraduates (of a specific university) and not the general population (they found no pre- post-outbreak differences). A recent search did not identify a new COVID peer-reviewed study among the general population on sleep with pre-outbreak data on sleep after we submitted our manuscript in February 2021.

We assume the reviewer refers to the systematic reviews on sleep by Souza et al. (2021), Jahrami et al. (2021) and Nochaiwong et al. (2021). These reviews were published after of just before we submitted our manuscript and therefore could not be included in the original manuscript. Importantly, the inclusion criteria and tables of the three reviews (with included studies published in the first months after the outbreak) show that all studies were cross-sectional in nature and often based on convenience samples. We hope that the reviewer agrees with our argument that without pre-COVID data on sleep (or comparable pre-COVID reference groups), no conclusions can be made about the effects of this pandemic on sleep (such as change in prevalence and incidence).

Based on this comment we added in the discussion (added text in Italics)

We are not aware of prospective population based COVID-19 studies to compare our findings on sleep problems, fatigue, use of pharmaceuticals, and use of mental health services use with. For example, sleep problems were assessed in many studies [38-40], but all studies used cross-sectional study designs and many were based on convenience samples.

5. Given how multi-factorial mental health is and the unique situation presented by the global pandemic, I wondered about the utility and how the interpretation of results could be used to positive effect within the field of mental health.

Response:

Thank you for this interesting question. We believe that reviewer 2 asked a somewhat similar question. We have tried to answer the question of this reviewer and reviewer 2 simultaneously. Therefore, we would like to refer to our response to comment 13.

6. I was also unsure as to the validity of an accurate comparison with the USA and UK when the measures differed between all the studies mentioned. Furthermore, in The Netherlands some questions failed to use validated measures, merely singular questions that were ‘similar’ to questions taken from validated measures.

Response:

We agree with the reviewer that we did not mention and discuss the possibility that differences in measures could be the reason for differences in outcomes between the UK and US studies on the one hand, and the Dutch studies on the other hand. We therefore added (added text in italics):

“Furthermore, mental disorders in the US were much more prevalent in the US than in the Netherlands which may increase the risk for higher post-outbreak mental health problems [40]. It might be that the Dutch welfare system provide better support to people with mental health issues during the COVID-19 outbreak or to people who ran into mental health issues after the outbreak than the US or UK welfare system does.

Finally, we used other questionnaires to examine mental health than the UK and USA studies did (for instance, we used the MHI-5 and not the GHQ-12 as in the UK and K6 as in the USA studies). It is unknown if our study would have yielded other results, specifically a strong increase in mental health problems after the COVID-19 outbreak, when we had administered the GHQ-12 or K6 instead of the MHI-5. However, given the high correlations between such mental health measures [51] we do not consider that very likely.”

7. Within the discussion, specifically pages 30-31, rhetorical reasoning appears, for example, suggesting Brexit as a reason for higher UK scores, or societal tensions dividing the UK and USA, or even COVID-19 and the surrounding political discourse. Unfortunately, there is no scientific evidence presented for these claims, which I felt weakened the paper.

Response:

In the section the reviewer refers to we tried to discuss differences in outcomes: what are possible reasons for these differences in outcomes (such as differences in unemployment, period in which studio took place, the prevalence of mental disorders before the outbreak, the health and welfare systems between countries).

We disagree with the reviewer’s comment that we made any claim with respect to the role of Brexit and presidential election in the US. We only offered a possible explanation. We wrote “Another possible explanation could be that the Brexit process and final end of the UK membership of the EU in 2020, similar to the US due to the presidential elections, strongly divided the country resulting in societal tensions and uncertainties about the future outside the EU. These tensions and uncertainties may have increased the risk of mental health problems. With respect to the political climate, other than the US where the COVID-19 pandemic became part of an intense political debate and elections, to date this pandemic did not result in a similar political discourse in the Netherlands as in the US.”.

However, we agree with the reviewer that we should have added references to support offering this possible explanation. We therefore added the following three publications in this section (we revised the sentence slightly)

“These tensions and uncertainties may cause stress and therefore may have increased the risk of mental health problems [47-49]”.

[47] APA. Presidential Election a Source of Significant Stress for More Americans than 2016 Presidential Race. https://www.apa.org/news/press/releases/2020/10/election-stress (accessed June 7 2021).

[48] O'Neill S. Brexit and Northern Ireland: leaders must consider the mental health of the population. Lancet Psychiatry. 2019; 6: 372-373. https://doi.org/10.1016/S2215-0366(19)30121-X

[49] Smith KB, Hibbing MV, Hibbing JR. Friends, relatives, sanity, and health: The costs of politics. PLoS ONE 2019; 14: e0221870. https://doi.org/10.1371/journal.pone.0221870

8. Furthermore, suggesting support in health systems as a potential reason for differences in results is problematic when services are structured and funded differently. This again fails to address the complexity.

Response:

Based on this comment we revised this section into:

“Furthermore, mental disorders in the US were much more prevalent in the US than in the Netherlands which may increase the risk for higher post-outbreak mental health problems [50]. It might be that the Dutch welfare and mental health care system provide better support to people with mental health issues during the COVID-19 outbreak or to people who ran into mental health issues after the outbreak than the US or UK welfare system and mental health care system does. Unemployed adults (or adults who lost their job due to this pandemic) can invoke for unemployment benefits and, in principle, each Dutch citizen has a health care insurance regardless of being employed or not in contrast to for example the US.”

9. Considering these claims overall left the discussion feeling somewhat unfocused, as if unsure of the story it wanted to tell. On arriving at the end of the paper, as a reader I wondered about originality and addition to the evidence base because of the previous papers using the same data set from the LISS panel and suggesting similar findings.

Response:

Following the comments of the reviewer we have revised some sections of the discussion and believe that we were able to address the comments as much as possible. We fully realize that our paper is not able to answer all relevant questions and that future research is needed to address these questions.

In our previous papers we also used the LISS panel but certainly not the same data. The current manuscript used for the first time data on mental health of the November-December 2020 survey. In addition, we examined for the first time prevalence, incidence and risk factors for sleep problems, fatigue, disabilities due to health, medicines for anxiety/depression, medicines for sleep problems, and use of mental health services among the general population in 2018, 2019 and 2020.

REVIEWER 2

10. This study examined the effects of COVID-19 pandemic on a comprehensive set of well-being outcomes including anxiety and depressive symptoms, sleep problems, fatigue, disabilities due to health problems, use of medicine for anxiety and depression, and mental health. Data were from the Longitudinal Internet studies for the Social Sciences (LISS) (N=4,064). This analysis is an extension to earlier covid related work using LISS investigating a longer time period and additional well-being outcome. Somewhat surprisingly, the authors found not significant increase in any of these outcomes. The authors conclude Dutch adults are resilient.

Response:

We agree with this summary. With respect to reviewer’s surprise, we would also like to refer to our response to comment 12.

11. While the study was well done, there are still some issues that need to be addressed:

1. It would be useful to provide more depth on the social, political, and epidemiological context in the Netherlands to provide more of a global perspective. Some of this is mention in the Discussion, but elaboration in the Introduction to "set the stage" would be most useful.

- For example, how wide spread was testing? Mitigation efforts? Government response? Public opinion?

Response:

Thank you for your kind compliment.

Based on this comment we added at the end of introduction (added text in Italics).

With respect to COVID-19 in the Netherlands, soon after the outbreak the Dutch government implemented large financial support programs for companies who significantly lost revenues because of the COVID-19 pandemic to allow them to keep people employed. In addition, governmental taxes were postponed. The Dutch governmental deficit increased in 2020 with 40 billion euro to 435 billion euro largely due to these financial programs [26]. In 2020 about 800.000 residents were tested positive for COVID-19, although the number of residents with COVID-19 in 2020 is presumably higher [27]. After the outbreak residents and companies were confronted with several (partial) lockdowns in 2020, including closed schools and universities. Statistics Netherlands (CBS) reported that about 169,000 had died in the Netherlands, 10% more than expected compared to previous years [28].”

We left the public opinions out of this summary because its takes a lot of space to address this topic correctly, and public opinions are outside the aim of the present study.

12. The authors speculate a bit for *why* there were no differences, yet other comparative countries, on balance, report lower well-being during pandemic. The reasons provided are not very well developed and need more fleshing out. This is a limitation in the paper.

Response:

We are not sure what the reviewer is asking for because we offered several possible explanations (based on the comments of reviewer 1, see comment 6, we have added an alternative reason, e.g. that we used other research instruments), such as low unemployment rates in the Netherlands, the Dutch governmental financial support programs for companies and organizations, the Dutch health care and welfare system where everybody has a health insurance, the absence of political tensions about COVID-19 as in the US, the absence of Brexit-related stress, and differences between the US and Netherlands in the prevalence of mental disorders (before this pandemic). Perhaps the reviewer want to share which other possible explanations the reviewer is thinking of.

However, after we re-read the discussion section with this comment in mind, we noticed that we did not clarify enough that the identified UK and US studies assessed mental health until the summer of 2020, while our studies examined the mental health at the end of 2020. This difference in study period may be relevant because of a published (on medRxiv) but not yet peer-reviewed review and meta-analysis of peer-reviewed and many other non-peer reviewed COVID-19 studies with pre-COVID-19 data on mental health (this study was published on a preprint server after we submitted our manuscript) by Robison et al. (2021: see https://doi.org/10.1101/2021.03.04.21252921). We became aware of this study because the authors requested some additional information about our study.

They found that “The overall increase in mental health symptoms was most pronounced during the early stages of the pandemic (March-April), before decreasing and being generally comparable to pre-pandemic levels by mid-2020…. Findings confirm that the initial outbreak of the pandemic was associated with a significant but statistically small increase in mental health symptoms” (extracted from abstract).

Following the comment of the reviewer and using this recent meta-analyses of true prospective studies, we added in the discussion section:

“In our study we focused on the mental health effects of this pandemic at the end of 2020, nine months after the outbreak. The identified studies with pre-COVID-19 outbreak data on mental health (see introduction) were aimed at the mental health effects during the first months after the outbreak. This differences in study period may be of relevance. A published but not yet peer-reviewed meta-analysis by Robinson et al. [37] of peer-reviewed and all other non-peer reviewed population-based studies (until January 11, 2011) with pre-COVID-19 data found that “The overall increase in mental health symptoms was most pronounced during the early stages of the pandemic (March-April), before decreasing and being generally comparable to pre-pandemic levels by mid-2020…. Findings confirm that the initial outbreak of the pandemic was associated with a significant but statistically small increase in mental health symptoms”. In the recent post-outbreak US population-based study by Riehm et al. [38] a similar pattern was found: by August 1, the odds of mental distress had returned to levels comparable to March 11.”

13. Finally, what can the international community learn from the Dutch experience?

Response:

Reviewer 1 had a somewhat similar question (see comment 5). Below we try to answer both questions simultaneously.

We believe it is a little bit too early to describe what can be learned from the Dutch experience (for both the international community and the field of mental health), although we tried to explain why our results differ from studies in the US and UK. Our possible explanations suggest that financial support programs, existing adequate social welfare and access to health care, absence of dominant political tensions and politization of preventive measure during the pandemic, etc., probably mitigate the negative effects of this pandemic.

Based on both comments we added at the end of the discussion:

“Final remarks

In either way, an important lesson that can be drawn from all prospective studies to date is that the large majority of the general population was capable to preserve their mental health during 2020, although this pandemic disrupted many aspects of life. Like in the years before this pandemic, a small part of the general population developed mental health problems that were not present before (in this case) the COVID-19 pandemic. Interestingly, the study by Pan et al. [56] showed that among people with depressive, anxiety, or obsessive-compulsive disorders symptoms did not increase during the first months after the outbreak (cf. [20]). We offered possible explanations for the differences in results between the studies in the UK and US on the one hand and the Netherlands on the other hand. Future comparative multi-country studies, including middle and low income countries, are needed to further disentangle the complex relationships between especially existing welfare and health care systems, the size and dosage of governmental financial support programs, political systems and tensions, preventive measures, and the mental health among the general population.”

14. Another major limitation is there is not theoretical development in the Introduction of the paper. The authors briefly mention "conservation of resources" ... but how does that operate? Provided a theoretical framework will help with rationale for analytic approach, interpretation of results and providing additional substantive meaning.

Response:

Based on this comment we added (added text in italics)

“Based on the Conservation of Resources (COR) theory of Hobfoll [3,4] we may expect that this ongoing pandemic has negative effects among the general population since it directly or indirectly threatens important resources such as safety and health (for instance by being infected, loss of a significant other), social contacts and support (for instance by social distancing and staying-at-home following lockdowns), work and income (for instance by loss of job or reduced work) among the general population. Resource loss is an important factor, like existing problems, in predicting the impact of stressful events on mental health such as this pandemic. However, according to the COR model [3,4] people also strive to obtain, retain, protect resources and to restore lost resources (such as social contacts, employment, housing, health) and their resilience should not be underestimated [3-6]. The duration of this pandemic may however undermine the capacities of individuals, communities, and countries to cope with the negative effects of this pandemic on the medium and longer term. This may cause stress and increase the risk for mental health problems.”

15. A few other, more minor, and editorial issues:

Typo on pg 16. The authors mention NS for non-response, yet writ "p<.05"

Response:

Thank you for this comment. We have replaced “….the non-response was not significantly (p < 0.05) associated with….” with “….the non-response was not significantly (p > 0.05

) associated with….”.

16. It would also be useful to know N with all 3 T, just 2, just T1 and T3 etc

Response:

Based on this comment we first added in the abstract.

“In total, 4,064 respondents with complete data participated at all three surveys.”

It is a little effort to provide these numbers, but we hesitate to include the numbers of those participated at T1 and T2 only (N=558), T1 and T3 only (N=190) , and T2 and T3 only (N=272).

In the method section we wrote “The total study sample consisted of 4,064 respondents with complete data across the three surveys (99%)”.

17. Internet surveys have notorious low response rates. How was the sample chosen? What makes it representative of the Dutch population? These issues weren't spelled out in the Methods.

Response:

We are very sorry, but we do not fully understand this comment. In the method section we described how the sample was chosen “This panel (LISS) is based on a traditional probability sample drawn from the Dutch population register of 16 years and older by Statistics Netherlands and administered by Centerdata”.

In addition, because not all respondents at T1 participated at T2 and T3 “We next weighted the data using 16 exclusive demographic profiles among the total adult Dutch population to optimize the representativeness of the current study, based on the data of Statistics Netherlands (see: https://opendata.cbs.nl/#/CBS/en/; in English). The 16 profiles were constructed using the variables sex (male, female), age (18-34, 35-49, 50-64, 65 years and older) and marital status (married and unmarried), yielding 2*4*2=16 demographic profiles. All findings are based on the weighted sample”. We therefore consider our sample representative of the Dutch population (of 16 years and older).

Regarding the response we clarified that “Data on mental health of adults were extracted from the longitudinal Health module, in particular the waves in November 2018 (T1: Ninvited =6,466, response=84.4%), in November 2019 (T2: Ninvited=5,954, response=86.4%), and in November 2020 (T3: Ninvited=6,832, response=83.6%). These response rates cannot be considered low.

Perhaps the reviewer got the impression that respondents themselves took the initiative to sign up for the LISS panel and participate. However, in the LISS panel respondents cannot sign up for the panel: they were asked to participate after Statistics Netherlands selected them (based on a probability sample of the Dutch population):

We therefore added (added text in italics).

“This panel is based on a traditional probability sample drawn from the Dutch population register of 16 years and older by Statistics Netherlands and administered by CentERdata. People cannot sign up themselves as a respondents for the LISS panel, so there is no issue of self-selection bias.”

18. The first paragraph of the Discussion simply repeats the aims; this needs reworking.

Response:

We agree with the reviewer that this section was too long. We have shorted this section into.

“The aims of the present prospective population-based study were to examine the prevalence, incidence, and risk factors for mental health problems and mental health services use among the adult general population 9 months after the COVID-19 outbreak, compared to before the outbreak (November-December 2018 and 2019). To optimize the representativeness of the study sample (N=4,064), data were weighted using 16 demographic profiles of the adult Dutch population.”

Decision Letter 1

Marcus Tolentino Silva

9 Aug 2022

PONE-D-21-04880R1The prevalence, incidence and risk factors of mental health problems and mental health services use before and 9 months after the COVID-19 outbreak among the general Dutch population. A 3-wave prospective study.PLOS ONE

Dear Dr. van der Velden,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR:

  • The text has improved with revisions. However, because it is unconventionally structured, our readers may interpret it more as a research report than an original article. My suggestion is to reorder the topics (introduction, methods, results and discussion) and subtopics as suggested by the STROBE checklist. My suggestion for the topics and subtopics:

  • Introduction: no subtopics: indicate what the study is about, why it was carried out, why it should be published, a brief summary of previous evidence, what is unknown about the research topic and the objectives.

  • Methods: with the subtopics: design, scenario, sample selection, data collection, statistical methods and ethical aspects.

  • Results: with the subtopics: sample composition, main finding, secondary findings.

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Please ensure that your decision is justified on PLOS ONE’s publication criteria and not, for example, on novelty or perceived impact.

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==============================

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We look forward to receiving your revised manuscript.

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Marcus Tolentino Silva

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #3: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #3: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

Reviewer #3: (No Response)

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have done well to address comments so speedily and thoroughly. All queries have been answered satisfactorily. The paper now explains reasoning and substantiates the suggestions within the paper.

Reviewer #3: - page 14: there is a typo, the range of the Cronbach alpha is 0 - 1, not 100.

- measures need more description: are they validated tools? do they measure a construct or are they a checklist? if they measure a construct, what is the intarnal structure?

- why were not calculated the cronbach alpha for all the measures?

- Acronyms:

- acronyms should be written in long form in the original language and then in their english form.

- I do not see the extended form of the MOS acronym.

- What does the acronym 'GEE' in the data analysis section means?

- acronym aOR is repeated in its long form after declared in the short one

- consider that p values cannot exceed 1, the authors may consider to report them without the zero before the decimal dot (APA-7 style).

cross-wise meaning?

- Table 4, 1: CIs of ORs need to be reported to understand the significance of results.

- Table 4, 2: reading and intepreting this table is not straightforward, it is possible to use another format/way of presenting it?

- in general, results are very detailed and I think that graphical representations of results are needed to give the readers information with an instant glance.

**********

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Reviewer #1: No

Reviewer #3: No

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PLoS One. 2022 Nov 10;17(11):e0276834. doi: 10.1371/journal.pone.0276834.r004

Author response to Decision Letter 1


22 Aug 2022

We gratefully thank reviewer 1 and 3, and the editor for the thoughtful and helpful comments. It helped us to further improve our manuscript. Below we have described how we responded to each comment.

COMMENTS EDITOR.

1) The text has improved with revisions. However, because it is unconventionally structured, our readers may interpret it more as a research report than an original article. My suggestion is to reorder the topics (introduction, methods, results and discussion) and subtopics as suggested by the STROBE checklist. My suggestion for the topics and subtopics:

Response:

Thank you for your suggestions. We have revised the manuscript using several suggestions you offered, to prevent a possible confusion as much as possible.

However, we do not fully understand your comment that our manuscript was unconventionally structured (besides the intro, which we revised (see below)) because we followed the PLOSONE guidelines (https://journals.plos.org/plosone/s/submission-guidelines) and the structure and sub headings hardly differs from our earlier papers published in PLOSONE (or that of other papers in PLOSONE covering social science research). For instance, PLOSONE requires a section “Materials and methods” while you (like many other journals) suggest the word “Methods”. Because in our experience the office is critical on this issue, we chose to use their wordings.

1. Introduction: no subtopics: indicate what the study is about, why it was carried out, why it should be published, a brief summary of previous evidence, what is unknown about the research topic and the objectives.

Response:

Following this comment we have eliminated the subheadings with respect to results of studies conducted in the USA, UK and Netherlands (which we added earlier based on a comment of a previous reviewer). To further improve the readability of the introduction (prevent a lengthy intro without sub headings) we also shortened the introduction by around 35%.

2. Methods: with the subtopics: design, scenario, sample selection, data collection, statistical methods and ethical aspects.

Response:

Please see our response to comment 1. We have replaced “Data analyses” with Statistical methods”.

3. Results: with the subtopics: sample composition, main finding, secondary findings.

Response:

Please see our response to comment 1. We do not have secondary findings.

4. Discussion: with the subtopics: synthesis of research results, validity, comparison with the literature (move here the part of previous studies present in the introduction), interpretation of findings (move the interpretations present in the results here), conclusions.

Response:

As described in our response to the comments we have revised/shortened the introduction section to a large extent. Because of this substantial revision we chose not to move parts of the intro to the discussion, also because we believe that the intro must show what is (not) known (at the time the research is conducted of course) and why the study is conducted.

The editor furthermore suggested to move the interpretations present in the results in the discussion. We have checked the text on these issues but could not find clear examples of interpretations other than presentations/explanations of tables/findings. Perhaps the editor can give us examples because we agree that interpretations/comparisons with other studies, conclusions, etc. belong in the discussion section (we need the help of the editor on this issue).

Other revisions

The meta-analysis of Robinson et al. was published in 2022 in JAD. We have updated the references and text about this important study. We furthermore corrected small errors and revised unclear sentences.

REVIEWER #1:

5. The authors have done well to address comments so speedily and thoroughly. All queries have been answered satisfactorily. The paper now explains reasoning and substantiates the suggestions within the paper.

Response

Thank you very much for your kind words of appraisal.

REVIEWER #3

6. page 14: there is a typo, the range of the Cronbach alpha is 0 - 1, not 100.

Response

Based on this comment we have replaced 0.85 with .85 .

7. Measures need more description: are they validated tools? do they measure a construct or are they a checklist? if they measure a construct, what is the internal structure?

Response

The MHI-5 is a validated and widely used inventory assessing anxiety and depression symptom levels. In research, as we did, the sum scores of the 5 item are used (see Ware et al., 1992; Means Christensen et al., 2005). The questions/single items (yes/no) such as sleep problems and fatigue are administered each year since the start of LISS panel in 2007 (and used in several other peer-reviewed studies (examples see below, and other papers we are preparing). Because all data of the LISS panel is open access, we assume that other researchers have used these variables too.

van der Velden PG, Bosmans MWG, van der Meulen E, Vermunt JK. Pre-event trajectories of mental health and health-related disabilities, and post-event traumatic stress symptoms and health: A 7-wave population-based study. Psychiatry Res. 2016;246:466-473. https://doi.org/10.1016/j.psychres.2016.10.024

van der Velden PG, Das M, Muffels R. The stability and latent profiles of mental health problems among Dutch young adults in the past decade: A comparison of three cohorts from a national sample. Psychiatry Res. 2019;282:112622. https://doi.org/10.1016/j.psychres.2019.112622

van der Velden PG, van Bakel HJA, Das M. Mental health problems among Dutch adolescents of the general population before and 9 months after the COVID-19 outbreak: A longitudinal cohort study. Psychiatry Res. 2022;311:114528. https://doi.org/10.1016/j.psychres.2022

8. Why were not calculated the cronbach alpha for all the measures?

Response

We computed the CA’s for the MHI-5 total scores. It is not possible to compute CA’s of single items, such as for “Do you regularly suffer from fatigue” and “How often did you use the following health services over the past 12 months?”

9. Acronyms should be written in long form in the original language and then in their english form.

Response

We have checked the manuscript and used the long format before using the acronyms (see also response next comment.

10. I do not see the extended form of the MOS acronym.

Response

Following this comment we have revised:

“5-item sub scale of the MOS 36-item short-form health survey [30, 31]).

into:

“5-item sub scale of the Medical Outcomes Study (MOS), 36-Item Short Form Survey Instrument (SF-36, [30, 31])).

11. What does the acronym 'GEE' in the data analysis section means?

Response

Based on the comment we have revised the sentence into (revision in italics):

“To examine the extent to which the prevalence of the seven assessed mental health problems after the COVID-19 outbreak in November-December 2020 (T3) changed compared to the prevalence in November-December 2018 (T1) and 2019 (T2), generalized estimating equations (GEE) for longitudinal ordinal data were conducted (GENLIN in SPSS version 28, using an autoregressive working correlation structure) with problems at T1, T2 and T3 as dependent variables (separate analyses for each dependent variable).”

12. Acronym aOR is repeated in its long form after declared in the short one

Response

The acronym aOR and CI were clarified in the first paragraph “non-response” and under each table presenting aOR’s and CI.

13. Consider that p values cannot exceed 1, the authors may consider to report them without the zero before the decimal dot (APA-7 style).

Response

Based on this comment we have deleted all leading zero’s.

14. cross-wise meaning?

Response

We would like to refer to the section ”Statistical methods”(in previous version entitled “Data analyses”, in which we explained why and how we conducted the analyses. Because of this (lengthy) clarification we originally had chosen not to repeat this in the results section. However, based on this comment we revised the sentence:

“Table 3 shows the incidence of mental health problems and services use at T2 and T3 among the total study sample and the results of crosswise multivariate logistic regression analyses showing that the incidence of the mental health problems and services use at T2 and T3 did not differ significantly.”

Into:

“Table 3 shows the incidence of mental health problems and services use at T2 and T3 among the total study sample and the results of crosswise multivariate logistic regression analyses (A1 incidence versus B2 incidence, and B1 incidence versus A2 incidence) showing that the incidence of the mental health problems and services use at T2 and T3 did not differ significantly.”

15. Table 4, 1: CIs of ORs need to be reported to understand the significance of results.

- Table 4, 2: reading and interpreting this table is not straightforward, it is possible to use another format/way of presenting it?

Response

1) It seems that something went wrong. The CIs of the aORs were all presented in the S2 Appendix risk factors (this appendix was referred to in the beginning of paragraph “Risk factors of mental health problems and services use”). When submitting the current revised version we will check if the appendix are included in the PDF’s.

2) We understand the comment of the reviewer, but we looked several times at this issue but did not find a workable alternative for presenting the results of the analyses (splitting the table 4 in 5 tables did not solve the problem of the space needed to present the results). For the reason mentioned by the reviewer, we already replaced the CI’s to the appendix to improve the readability as much as possible (cf. Qian & Tahara, 2020, Table 3 (https://doi.org/10.1371/journal.pone.0235883). We are sorry, but we could not find a better way to present the results.

16. in general, results are very detailed and I think that graphical representations of results are needed to give the readers information with an instant glance.

Response

We thank the reviewer for the invitation to consider/think about a graphical presentation of our findings (besides/instead of a table(s)). We started the exercise with Table 4 and looked at the possibilities/usefulness of a forest-like graph in which the aORs and CIs are presented/plotted. We first noticed that this would require at least 5 graphs (because of the five dependent variables, with two rows for each predictor (2018, 2019). We next looked at the aORs in Table 4 to check if all aORs can be depicted in one forest plot for each dependent variable. Unfortunately, we had to conclude that this was not possible/workable because for instance the aORs for sleep problems and fatigue were rather high (≥ 214.07, not surprising given the high prevalence of sleep problems and fatigue among those with exiting sleep problems and fatigue ) compared to the aORs of for instance marital status (≤1.35). Including both aOR in one forrest plot would make the lower aORs almost invisible.

Decision Letter 2

Marcus Tolentino Silva

14 Sep 2022

PONE-D-21-04880R2The prevalence, incidence and risk factors of mental health problems and mental health services use before and 9 months after the COVID-19 outbreak among the general Dutch population. A 3-wave prospective study.PLOS ONE

Dear Dr. van der Velden,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR: Please make the corrections marked by the reviewer.

==============================

Please submit your revised manuscript by Oct 29 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Marcus Tolentino Silva

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #4: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #4: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #4: I Don't Know

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

Reviewer #4: Yes

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Reviewer #1: No

Reviewer #4: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This paper is improved from my initial reading and the decision to rewrite the introduction means it now makes much more sense. However, there remain some flaws in the work, which could be addressed.

Place the last paragraph on pp. 8-9 before the aim of the study so it flows neatly.

Ethical approval/informed consent p. 10; it would probably be wise to give the reason why ethics was not needed; aggregated anonymised data. Agree with mentioning that participants had agreed for further analysis of their data.

p.11, p. 16, Table 2, Table 3 etc.,: ‘disabilities due to mental health problems’. This could perhaps be worded as reduced or impaired functioning and use the ICF language. Disability using the social model refers to the barriers within society, used otherwise it places the ‘problem’ within the individual and makes the paper biomedical and lacking in consideration for social barriers. This makes people the problem. Means-Christensen et al. do not use the term disability in relation to psychological distress, they use impaired functioning (p. 566) which is the language of the ICF, as such the article is somewhat misrepresented.

Likewise, reword mental health problems throughout the paper to mental health difficulties. Language is extremely important so we do not reify and marginalise groups.

The term ‘eating problems’ could be amended. I thought these were eating disorders, are these identified by type in the LISS data? Then sleep problems are not identified, this could be a critique of the LISS data collection, does it mean disturbance in circadian rhythms, insomnia, or does it mean sleep disorders such as breathing-related sleep disorders? Alternatively, are a number of conditions/disorders aggregated under one heading? A little more clarity and critique here about the data would open the study out.

p.22: 2nd sentence, should it not be that existing mental health difficulties and service use were the strongest predictor for continued mental health difficulties and service use before and after the COVID-19 pandemic?

Services use should be service use throughout the paper, or use of services. Appreciate this a language issue.

p.29, 2nd paragraph: ‘people who ran into mental health issues’ people experience mental health difficulties, they do not ‘run into them’ please amend.

Limitations: this section goes further than strengths and limitations, so place some of this in a conclusion.

Final remarks section: I am not convinced of the rationale in the comments in this section because I feel it adds little to the paper. Offering differences between the UK, Netherlands and USA (observed from other studies, not analysed statistically) was not the aim of the paper and adding these last six lines detracts from the work done. The conclusion needs to focus on the paper, summing it up and its addition/contribution to existing research. I would delete this section and rewrite. Perhaps call it conclusion rather than final remarks begin with prospective studies and use some of the limitation section, which is more suited to a conclusion section. For example, the results suggesting further research using clinical interviews to provide more insight and future studies on mental health difficulties, eating disorders etc.

Reviewer #4: Dear authors,

I consider the comments raised by the reviewers in the previous round of reviews were successfully addressed. Congratulations for your effort on that.

**********

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Reviewer #1: No

Reviewer #4: No

**********

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PLoS One. 2022 Nov 10;17(11):e0276834. doi: 10.1371/journal.pone.0276834.r006

Author response to Decision Letter 2


27 Sep 2022

We thank the reviewers very much for their time and effort. It certainly helped us to improve our manuscript.

Reviewer #1:

1. This paper is improved from my initial reading and the decision to rewrite the introduction means it now makes much more sense. However, there remain some flaws in the work, which could be addressed.

Response:

Thank you for your kind words.

2. Place the last paragraph on pp. 8-9 before the aim of the study so it flows neatly.

Response:

We have moved this section as suggested and renumbered the references.

3. Ethical approval/informed consent p. 10; it would probably be wise to give the reason why ethics was not needed; aggregated anonymised data. Agree with mentioning that participants had agreed for further analysis of their data.

Response:

Based on this comment, we have revised the first sentence as follows:

“Since our research did not impose certain (experimental) behavior, our research did not need the approval of a Dutch Medical Ethical Testing committee according to the Dutch Law (see https://english.ccmo.nl/investigators/legal-framework-for-medical-scientific-research/your-research-is-it-subject-to-the-wmo-or-not).”

4. p.11, p. 16, Table 2, Table 3 etc.,: ‘disabilities due to mental health problems’. This could perhaps be worded as reduced or impaired functioning and use the ICF language. Disability using the social model refers to the barriers within society, used otherwise it places the ‘problem’ within the individual and makes the paper biomedical and lacking in consideration for social barriers. This makes people the problem. Means-Christensen et al. do not use the term disability in relation to psychological distress, they use impaired functioning (p. 566) which is the language of the ICF, as such the article is somewhat misrepresented.

Response:

Based on this comment and to prevent possible confusion we have replaced “disabilities” with “impaired functioning” throughout the manuscript, including the tables and appendix 1 and 2.

5. Likewise, reword mental health problems throughout the paper to mental health difficulties. Language is extremely important so we do not reify and marginalise groups.

Response:

We fully agree with the reviewer that language is very important. However, we do not understand that the term “mental health problems” marginalizes groups. In addition, a search on PUBMED with the term “mental health problems” identified 16,461 papers while as search with the term "mental health difficulties" identified “only” 1,226 papers, clearly suggesting that “mental health problems” is an often used and well accepted used term (we used this term in all our papers). For these reasons we did not reword the term “mental health problems”.

6. The term ‘eating problems’ could be amended. I thought these were eating disorders, are these identified by type in the LISS data? Then sleep problems are not identified, this could be a critique of the LISS data collection, does it mean disturbance in circadian rhythms, insomnia, or does it mean sleep disorders such as breathing-related sleep disorders? Alternatively, are a number of conditions/disorders aggregated under one heading? A little more clarity and critique here about the data would open the study out.

Response:

Based on this comment we have replaced “eating problems” with “eating disorders”. In addition, we added:

“As described, sleep problems, fatigue and impaired functioning were assessed by one item questions. Future research is needed to examine the course of different aspects of sleep problems, fatigue and impaired functioning”.

7. p.22: 2nd sentence, should it not be that existing mental health difficulties and service use were the strongest predictor for continued mental health difficulties and service use before and after the COVID-19 pandemic?

Response:

We understand the comment of the reviewer, but to be able to state that existing mental health difficulties and service use were the strongest predictor for continued mental health difficulties and service use before and after the COVID-19 pandemic, different analyses are required. In this case the dependent variables should be persistent mental health problems and service use.

8. Services use should be service use throughout the paper, or use of services. Appreciate this a language issue.

Response:

We have revised the text using the term “service use”.

9. p.29, 2nd paragraph: ‘people who ran into mental health issues’ people experience mental health difficulties, they do not ‘run into them’ please amend.

Response:

Thank you for noticing this error. We have corrected this mistake.

10. Limitations: this section goes further than strengths and limitations, so place some of this in a conclusion.

Response:

Based on this comment we moved the sentence “Monitoring of the mental health of the general population is needed because the duration of this pandemic on the longer term may undermine the capacity of individuals to cope with the consequences” to the final conclusions section.

11. Final remarks section: I am not convinced of the rationale in the comments in this section because I feel it adds little to the paper. Offering differences between the UK, Netherlands and USA (observed from other studies, not analysed statistically) was not the aim of the paper and adding these last six lines detracts from the work done. The conclusion needs to focus on the paper, summing it up and its addition/contribution to existing research. I would delete this section and rewrite. Perhaps call it conclusion rather than final remarks begin with prospective studies and use some of the limitation section, which is more suited to a conclusion section. For example, the results suggesting further research using clinical interviews to provide more insight and future studies on mental health difficulties, eating disorders etc.

Response:

Based on this comment we replaced “final remarks” with “final conclusions”.

We are sorry, but we disagree with reviewer’s comments on this section. It is the task of researchers to compare the findings of other researchers with their findings. This is what we did in the discussion section. We therefore do not understand reviewers remark “Offering differences between the UK, Netherlands and USA (observed from other studies, not analysed statistically) was not the aim of the paper ……”. In addition, in line with the comments of the reviewer we stated “Future comparative multi-country studies, including middle and low-income countries, are needed to further disentangle the complex relationships between especially existing welfare and health care systems, the size and dosage of governmental financial support programs, political systems and tensions, preventive measures, and mental health among the general population”.  

Reviewer #4:

Dear authors,

12. I consider the comments raised by the reviewers in the previous round of reviews were successfully addressed. Congratulations for your effort on that.

Response:

Thank you for your compliments.

Attachment

Submitted filename: letter to reviewers 19-8-2022.docx

Decision Letter 3

Marcus Tolentino Silva

17 Oct 2022

The prevalence, incidence, and risk factors of mental health problems and mental health service use before and 9 months after the COVID-19 outbreak among the general Dutch population. A 3-wave prospective study.

PONE-D-21-04880R3

Dear Dr. van der Velden,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Marcus Tolentino Silva

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Acceptance letter

Marcus Tolentino Silva

20 Oct 2022

PONE-D-21-04880R3

The prevalence, incidence, and risk factors of mental health problems and mental health service use before and 9 months after the COVID-19 outbreak among the general Dutch population. A 3-wave prospective study.

Dear Dr. van der Velden:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

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on behalf of

Dr. Marcus Tolentino Silva

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 Appendix. Age categories.

    (DOCX)

    S2 Appendix. Risk factors.

    (DOCX)

    Attachment

    Submitted filename: letter to reviewers 19-8-2022.docx

    Data Availability Statement

    The study was conducted using the Dutch Longitudinal Internet studies for the Social Sciences (LISS) pane. The LISS panel started in 2007 and is based on a large traditional probability sample drawn from the Dutch population. The Dutch Research Counsel (NWO) funded the set-up of LISS. Panel members receive an incentive of €15 per hour for their participation and those who do not have a computer and/or Internet access are provided with the necessary equipment at home. Further information about all conducted surveys and regulations for free access to the data can be found at https://www.dataarchive.lissdata.nl/ (in English). The LISS panel has received the international Data Seal of Approval (see https://www.datasealofapproval.org/en/). All data of studies conducted with the LISS panel are anonymized.


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