Abstract
Purpose
EGOS is an epidemiological obsessive–compulsive disorder (OCD) cohort in Sweden. Individuals contributed DNA for genotyping and sequencing and completed a Swedish translation of the Obsessive–Compulsive Inventory-Revised (OCI-R), a self-report questionnaire for assessing the severity of OCD. This study aimed first to evaluate the psychometric properties of the Swedish translation of the OCI-R and then shed light on the frequency, severity, and symptom dimensions of OCD comorbid with other psychiatric disorders.
Methods
OCI-R data were available for 1010 individuals diagnosed with OCD, and 124 individuals diagnosed with chronic tic disorders without OCD used as a comparison group. We first performed a confirmatory factor analysis to confirm the six-factor structure of OCI-R. Then, we estimated Cronbach’s α coefficient and the generalizability coefficient to evaluate the internal consistency of the OCI-R. We linked the data from the Swedish national registries to access and analyze psychiatric comorbidities of OCD.
Results
The Swedish translation of OCI-R demonstrated internal consistency and clear agreement with the OCI-R six-factor model. The mean total OCI-R score for females was significantly higher than for males. The most comorbid psychiatric condition to OCD were anxiety disorders (13.6%) and major depression (12%).
Conclusion
The Swedish translation of OCI-R was a valid and reliable measure for assessing the severity of OCD. We observed that individuals with OCD frequently had additional comorbid psychiatric disorders and that the severity of OCD was significantly higher in individuals with at least one additional psychiatric comorbidity as compared to individuals with no psychiatric comorbidity.
Keywords: Obsessive–compulsive inventory-revised, Swedish translation, Comorbidities, Symptoms dimension
Introduction
Obsessive–compulsive disorder (OCD) is a common psychiatric disorder characterized by intrusive and unwanted thoughts, images, or urges (obsessions) and repetitive behaviors (compulsions) that function to reduce the distress caused by obsessions. Certain aspects of the approach to the diagnostic classification of OCD differ between the International Classification of Diseases (ICD)-10 and the Diagnostic and Statistical Manual of Mental Disorders (DSM)-5; however, the essential features of OCD are the same in both systems: recurrent obsessions and compulsions [1]. The prevalence of OCD is estimated at 0.75–2.5% of the general population [2–8].
OCD is a clinically and etiologically heterogeneous condition and has four broad primary categories of symptom dimensions that are not mutually exclusive: (1) symmetry (symmetry obsessions, repeating, ordering, and counting compulsions), forbidden thoughts (aggressive, sexual, religious, and somatic obsessions, and checking compulsions), cleaning (contamination obsessions and washing and cleaning compulsions), and hoarding [9]. However, hoarding is now classified in DSM-5 as a distinct entity under the category of Obsessive–Compulsive and Related Disorders [10].
The Obsessive–Compulsive Inventory-Revised (OCI-R) is a self-report questionnaire that is designed to assess the severity and type of symptoms that are typically present in OCD [11]. By answering 18 questions, individuals rate the degree to which they are bothered or distressed during the past month by specific, common OCD symptoms, using a 5-point scale from “not at all” (0 points) to “extremely” (4 points). The OCI-R measures six symptom dimensions of OCD labeled as: Ordering, Obsessing, Checking, Cleaning, Hoarding, and Neutralizing. The OCI-R is a well-established instrument with excellent psychometric properties [11] and valid measures of OCD symptom severity [11]. It has high test–retest reliability, convergent validity, good internal consistency, and solid factor structure according to both clinical [11–13] and nonclinical cohorts [14, 15]. OCI-R has performed well in discriminating OCD from anxiety disorders [11, 16].
The OCI-R correlates with the widely-accepted OCD severity rating assessment scale, the Yale-Brown Obsessive–Compulsive Scale (Y-BOCS) [16–18]. However, OCI-R covers a subset of the scales included in Y-BOCS and does not directly measure time occupied, interference, resistance, or control related to OCD (the remaining Y-BOCS subscales).
Abramovitch et al. compared the OCI-R subscales with the Dimensional Obsessive–Compulsive Scale (DOCS) [19]. The DOCS is a 20-item self-report questionnarie that measures OCD severity across four symptom dimensions. They observed that the Washing subscale was a significant predictor of DOCS contamination scores; the Checking subscale was a significant predictor of DOCS Responsibility For Harm scores; the Obsessing subscale was a significant predictor of DOCS Unacceptable/Taboo Thoughts scores; and the Ordering subscale was a significant predictor of DOCS Symmetry scores. The Neutralizing subscale was not strongly correlated with any of the DOCS subscales.
The translated versions of the OCI-R into Norwegian [20], Spanish [21], German [13], Icelandic [22], and Mandarin-Chinese [23] have shown satisfactory psychometric properties. A Swedish translation of the OCI-R has been available since 2009. Despite the extensive use in Swedish clinical settings, no evaluation of the psychometric properties has been made previously. The goal of this study was to evaluate the psychometric properties of the Swedish OCI-R and shed light on the frequency, severity, and symptom dimensions of OCD comorbid with other psychiatric conditions.
Method
Translation
The OCI-R was translated into Swedish by Anna Grönberg and Sandra Bates in 2009, based on the original OCI-R questionnaire Foa et al. [11], with permission from the original authors and without copyright. Drs. Anna Grönberg and Sandra Bates are licensed psychologists and psychotherapists, both fluent in English and Swedish. The OCI-R was translated from English to Swedish and then back-translated to English. This procedure was repeated to achieve maximum linguistic congruence.
Study population
In this study, we used data collected from study participants in EGOS (Epidemiology and Genetics of Obsessive–Compulsive Disorder and Chronic Tic Disorders in Sweden), one of the largest ongoing population-based cohort studies in Sweden, with the overall aim to identify genetic and possible environmental risk factors for obsessive–compulsive disorder (OCD) and Tourette disorder and related chronic tic disorders (CTD) [24]. The EGOS study has been led by Professor Dorothy Grice and is the result of a collaboration between Icahn School of Medicine at Mount Sinai, New York, USA, and Karolinska Institutet, Stockholm, Sweden. Ethical approval was obtained from the Institutional Review Board at the Icahn School of Medicine at Mount Sinai, New York, USA, and the Regional Ethical Review Board in Stockholm, Sweden.
EGOS is built upon clinical diagnoses of OCD and CTD in specialized psychiatric care by the treating physician. In the EGOS study, all individuals living in Sweden with a clinical diagnosis of OCD or CTD by a psychiatrist and found in the Swedish National Patient Register (NPR) were eligible for inclusion in the source population. In the NPR, diagnoses are recorded using the International Classification of Disease (ICD) criteria. Individuals with at least two clinical diagnoses of OCD or CTD in the source population were contacted to join the study and provide either a blood or saliva sample. DNA was extracted from the samples upon arrival at the Biobank. All samples were genotyped using the Global Screening Array and analyzed for common genetic variation [25]. All samples are currently going through whole-exome sequencing to detect rare structural variation and single nucleotide variation. The Swedish translation of OCI-R was provided as a web questionnaire to all participants (for more details, see the EGOS cohort profile [24]).
The age of onset was not available for this study. We used the date of the first registered diagnosis in the NPR that led to the diagnosis of OCD or CTD as the age of diagnosis. Individuals diagnosed early must have had an early onset of OCD or CTD; however, individuals diagnosed late could have experienced early onset OCD or CTD, but were diagnosed later in their lives. All individuals who seek healthcare through the national healthcare system have their diagnostic data entered into the NPR. These data include the ICD code for the primary diagnosis and up to thirty ICD-codes for non-primary diagnosis at each healthcare visit. In this study, we considered an individual to have a co-morbid condition if the condition was documented as the primary diagnosis for at least one time point.
Our study population in this work consisted of 1134 individuals who had completed the Swedish translation of the OCI-R questionnaire by June 2019.
Statistical analysis
We used the psych package developed by William Revelle in R [26]. We performed a confirmatory factor analysis to confirm the six-factor structure of OCI-R and address the construct validity. We used the criteria recommended by Hu and Bentler [27]: (1) χ2 statistic and the p value: a non-significant result suggests that the model fits. The statistic becomes most likely significant for large samples; (2) Comparative fit index (CFI): should be ≥ 0.95; (3) Root mean squared error of approximation (RMSEA) including 90% CI: RMSEA should be ≤ 0.05, upper confidence interval (CI) bound ≤ 0.10; (4) Standardized root mean square residual (SRMR): should be ≤ 0.08 [28].
For internal consistency reliability, we estimated Cronbach’s α coefficient. Cronbach’s α reflects how closely related a set of test items are as a group.
OCI-R score is sensitive to treatment effects, and pre- to post changes in OCI-R score could reflect an improvement in OCD [29]. Given that our source population was sampled from those in specialized psychiatric care, we anticipate that most individuals received some treatment. We analyzed the association between the latest diagnosis date in the NPR and the date the individual completed the OCI-R questionnaire (we refer to it as time difference). We adjusted the total OCI-R score using the time difference as a covariate in linear regression. We also adjusted Cronbach’s α coefficient using multi-facet G-theory and applying the time difference as a facet.
Results
Demographic data and frequency of comorbid psychiatric conditions
OCI-R data for 1134 individuals were available for this study. Among 1134 individuals, 1010 had a diagnosis of OCD with an average diagnosis age of 22.1 (SD = 7.0). OCD was more common among females than males (65% vs. 35%). We explored the frequency of comorbid psychiatric disorders with OCD. Anxiety disorders (phobic anxiety disorders, ICD 10: F40, and other anxiety disorders, ICD 10: F41) (30%) and major depressive disorder (25%) were the most common comorbid diagnoses (Table 1). One hundred twenty-four individuals had CTD without OCD (34% female).
Table 1.
Characterization of the comorbid conditions with OCD
| Total (%) | Diagnosed1 < 18 y.o. (%) | Diagnosed ≥ 18 y.o. (%) | |
|---|---|---|---|
|
| |||
| OCD | 1010 | 296 | 713 |
| Female | 658 (65%) | 188 (64%) | 469 (66%) |
| OCD and CTD | 83 (8%) | 49 (17%) | 33 (5%) |
| Female | 37 (44%) | 27 (55%) | 9 (27%) |
| OCD without CTD | 927 (92%) | 247 (83%) | 680 (95%) |
| Female | 621 (67%) | 161 (65%) | 460 (68%) |
| CTD without OCD | 124 (12%) | – | – |
| Female | 42 (34%) | ||
| OCD and ADHD | 76 (8%) | 32 (11%) | 43 (6%) |
| Female | 41 (54%) | 13 (41%) | 27 (63%) |
| OCD and intellectual disability | 8 (< 1%) | 3 (1%) | 5 (< 1%) |
| Female | 4 (50%) | 0 (41%) | 3 (60%) |
| OCD and autism spectrum disorder | 64 (6%) | 33 (11%) | 31 (4%) |
| Female | 28 (43%) | 11 (33%) | 17 (55%) |
| OCD and anxiety disordersa | 301 (30%) | 56 (19%) | 244 (34%) |
| Female | 202 (67%) | 35 (63%) | 166 (68%) |
| OCD and eating disorder | 71 (7%) | 22 (7.4%) | 49 (7%) |
| Female | 69 (97%) | 21 (95%) | 48 (98%) |
| OCD and borderline personality disorder | 26 (3%) | 3 (1%) | 23 (3%) |
| Female | 26 (100%) | 3 (100%) | 23 (100%) |
| OCD and major depressive disorder | 225 (25%) | 67 (23%) | 188 (26%) |
| Female | 163 (64%) | 45 (67%) | 118 (63%) |
| OCD and schizophrenia | 10 (< 1%) | 5 (2%) | 5 (< 1%) |
| Female | 5 (50%) | 4 (80%) | 1 (20%) |
| OCD and bipolar disorder | 48 (5%) | 8 (3%) | 40 (6%) |
| Female | 36 (75%) | 7 (88%) | 29 (73%) |
| OCD, ADHD, and CTD | 27 (3%) | 18 (6%) | 8 (1%) |
| Female | 13 (48%) | 7 (39%) | 5 (63%) |
| OCD with at least one comorbid psychiatric disorder | 416 (41%) | 116 (40%) | 299 (42%) |
| Female | 264 (63%) | 71 (61%) | 192 (64%) |
| OCD without any psychiatric comorbidities | 594 (60%) | 180 (61%) | 414 (58%) |
| Female | 394 (66%) | 117 (65%) | 277 (67%) |
ADHD attention-deficit hyperactivity disorder, CTD tourette disorder and related chronic tic disorders, OCD obsessive–compulsive disorder. y.o. years of age
Phobic anxiety disorders (F40), and other anxiety disorders (F41)
One case missing
We compared the characteristics of individuals with OCD who were diagnosed before the age of 18 (early diagnosis age) and after the age of 18 (late diagnosis age). In both age categories, OCD was more common in females than males. Among individuals with late diagnosis age, anxiety disorders, major depressive disorder, eating disorders, and ADHD were the most common psychiatric comorbidities. In contrast, among individuals with early diagnosis age, major depressive disorder, anxiety disorders, CTD, and autism spectrum disorder were most common.
41% of individuals with OCD had at least one additional psychiatric comorbidity, with about a similar rate for individuals diagnosed before or after the age of 18.
Psychometric properties and construct validity
Confirmatory factor analysis
We performed a confirmatory factor analysis with six factors: Washing, Obsessing, Hoarding, Ordering, Checking, and Neutralizing. We estimated χ2 (120) = 401.056 (p = 0.000), RMSEA = 0.048 (90% CI 0.043, 0.053), TLI = 0.996, SRMR = 0.043 and CFI = 0.997. According to these values, the six-factor structure of the original version of the OCI-R was supported based on the criteria recommended by Hu and Bentler [27].
The model of the confirmatory factor analysis is illustrated in Fig. 1. The standardized factor weights are shown on the arrows. The correlations between the factors were between 0.39 and 0.52, indicating that the subscales were related to each other but not redundant.
Fig. 1.
Model of the confirmatory factor analysis for the Swedish translation of Obsessive–Compulsive Inventory-Revised (OCI-R). All estimates are standardized. Rectangles represent latent variables (questions in OCI-R). Circles represent factors. Correlations between factors are shown by double-headed arrows. Values next to arrows between the latent variables (questions) and the factors are standardized regression weights. The closer they are to one, the larger they are to account for the variation in that factor
Internal consistency
The Cronbach’s α coefficient for the total score was 0.9 [95% CI 0.89–0.91]. The results for the subscales were: Washing, α = 0.88; Obsessing, α = 0.85; Hoarding, α = 0.87; Ordering, α = 0.88; Checking, α = 0.89; and Neutralizing, α = 0.87 (Table 2). The α values for OCD cases were close to the reported α values for the original OCI-R reported by Foa et al. (Washing α = 0.86, Obsessing α = 0.82, Hoarding α = 0.90, Ordering α = 0.90, Checking α = 0.88, Neutralizing α = 0.86) [11]. We also used G-theory to calculate the generalizability coefficient using variance components, a reliability coefficient equivalent to Cronbach’s α. The generalizability coefficient decreased slightly after adjusting for the time differences between the latest diagnosis date and the date that individuals completed the OCI-R (using time differences as facet) (Table 2).
Table 2.
Internal consistency for the Swedish translation of the Obsessive–Compulsive Inventory-Revised (OCI-R)
| OCD | CTD without OCD | OCD | ||
|---|---|---|---|---|
|
|
|
|
||
| Cronbach’s α coefficient (95% CI) | Cronbach’s α coefficient (95% CI) | Generalizability before adjustment | Generalizability after adjustment | |
|
| ||||
| Total score | 0.90 (0.89–0.91) | 0.85 (0.81–0.89) | 0.900 | 0.897 |
| Obsessing | 0.85 (0.84–0.87) | 0.85 (0.80–0.89) | 0.851 | 0.848 |
| Washing | 0.88 (0.87–0.89) | 0.80 (0.73–0.86) | 0.882 | 0.876 |
| Hoarding | 0.87 (0.86–0.88) | 0.70 (0.61–0.80) | 0.870 | 0.870 |
| Ordering | 0.88 (0.87–0.89) | 0.82 (0.76–0.87) | 0.881 | 0.879 |
| Checking | 0.89 (0.87–0.90) | 0.83 (0.78–0.88) | 0.887 | 0.887 |
| Neutralizing | 0.87 (0.86–0.89) | 0.70 (0.60–0.79) | 0.874 | 0.872 |
CTD tourette disorder and related chronic tic disorders, OCD obsessive–compulsive disorder
We calculated Cronbach’s α coefficient for individuals with CTD without OCD (Table 2). For this group, Cronbach’s α coefficients were closer to the control populations reported in a study using a Norwegian translation of OCI-R [20].
Population characteristics of obsessive–compulsive symptoms
The mean total OCI-R score for individuals with OCD was 22.5 (SD = 13.6) and after adjusting for the time difference was 29.0 (SD = 13.0) (Table 3). In addition, females with OCD had significantly higher OCI-R scores as compared to males (23.3 vs. 20.9, p value < 0.01).
Table 3.
Obsessive–Compulsive Inventory-Revised (OCI-R) score for individuals with OCD and other comorbid conditions
| Total OCI-R score (SD) | |
|---|---|
|
| |
| OCD | 22.5 (13.6) |
| Female | 23.3 (13.9) |
| Male | 20.9 (12.8) |
| OCD and CTD | 20.0 (13.2) |
| Female | 21.4 (15.0) |
| Male | 18.9 (11.6) |
| OCD without CTD | 22.7 (13.6) |
| Female | 23.4 (13.9) |
| Male | 21.2 (12.9) |
| CTD without OCD | 14.3 (9.8) |
| Female | 17.7 (11.4) |
| Male | 12.6 (8.5) |
| OCD and ADHD | 25.4 (15.6) |
| Female | 30.9 (15.6) |
| Male | 19.1 (12.3) |
| OCD and intellectual disability | 26.6 (19.6) |
| Female | 40.8 (16.1) |
| Male | 12.5 (10.4) |
| OCD and autism spectrum disorder | 22.4 (13.2) |
| Female | 22.3 (14.2) |
| Male | 22.4 (12.5) |
| OCD and anxiety disordersa | 24.7 (14.0) |
| Female | 25.5 (14.8) |
| Male | 22/9 (12.3) |
| OCD and eating disorder | 27.3 (16.1) |
| Female | 27.0 (16.4) |
| Male | 34.5 (-) |
| OCD and borderline personality disorder | 30.1 (14.3) |
| Female | 30.1 (14.3) |
| Male | 0 |
| OCD and major depressive disorder | 24.1 (15.0) |
| Female | 25.9 (15.6) |
| Male | 21.0 (13.6) |
| OCD and schizophrenia | 26.1 (21.8) |
| Female | 29.0 (19.6) |
| Male | 23.2 (25.8) |
| OCD and bipolar disorder | 29.4 (15.3) |
| Female | 30.8 (15.9) |
| Male | 25.2 (12.7) |
| OCD, ADHD, and CTD | 17.1 (14.3) |
| Female | 22.9 (17.3) |
| Male | 11.9 (8.3) |
| OCD with at least one comorbid psychiatric disorder | 24.1 (14.1) |
| Female | 25.4 (14.8) |
| Male | 21.9 (12.5) |
| OCD without any psychiatric comorbidities | 21.4 (13.2) |
| Female | 22.0 (13.2) |
| Male | 20.9 (13.0) |
| OCD diagnosed < 18 y.o | 20.3 (12.7) |
| Female | 21.9 (13.6) |
| Male | 17.6 (10.7) |
| OCD diagnosed ≥ 18 y.o | 23.3 (13.8) |
| Female | 23.8 (14.0) |
| Male | 22.4 (13.3) |
ADHD attention-deficit/hyperactivity disorder, CTD Tourette disorder and related chronic tic disorders, OCD obsessive–compulsive disorder. y.o. years of age
Phobic anxiety disorders (F40), and other anxiety disorders (F41)
The mean total OCI-R score for individuals with CTD and without OCD was 14.3 (SD = 9.8), and it was slightly higher than the control populations reported in the other studies (8.3 (SD = 9.2) in [30], and 10.4 (SD = 9.2) in [20]). OCI-R score of individuals with OCD was significantly higher than individuals with CTD without OCD (22.1 vs. 14.3, p value < 0.01).
Individuals with OCD and at least one comorbid psychiatric disorder had significantly higher OCI-R scores than individuals with OCD without any psychiatric comorbidity (24.1 vs. 21.4, p value < 0.01). In particular, the mean total OCI-R score for individuals with OCD and borderline personality disorder (OCI-R = 30.1, p value < 0.01), OCD and bipolar disorder (OCI-R = 29.4, p value < 0.01), OCD and eating disorder (OCI-R = 27.3, p value < 0.01), OCD and ADHD (OCI-R = 25.4, p value = 0.03), OCD and anxiety disorder (OCI-R = 24.7, p value < 0.01), and OCD and depression (OCI-R = 24.1, p value = 0.01) were significantly higher than individuals with OCD without any psychiatric comorbidity (OCI-R = 21.4).
Individuals with late OCD diagnosis age (≥ 18 years of age) had significantly higher OCI-R scores than individuals with early OCD diagnosis age (< 18 years of age) (OCI-R 23.4 vs. 20.3, p value < 0.001).
We compared the OCI-R subscales of individuals with different comorbid psychiatric conditions (Table 4 and Table S1). Scores for Washing, Obsessing, Checking, and Neutralizing of individuals with OCD were significantly different from the scores of individuals with CTD without OCD (p value < 0.01). For Ordering and Hoarding, the differences were not significant.
Table 4.
Obsessive–Compulsive Inventory-Revised (OCI-R) subscales
| Washing (SD) | Obsessing (SD) | Hoarding (SD) | Ordering (SD) | Checking (SD) | Neutralizing (SD) | |
|---|---|---|---|---|---|---|
|
| ||||||
| OCD | 4.01 (3.68) | 5.29 (3.36) | 2.08 (2.66) | 3.93 (3.35) | 4.34 (3.33) | 2.82 (3.44) |
| Female | 4.34 (3.80) | 5.34 (3.33) | 2.05 (2.69) | 4.18 (3.46) | 4.51 (3.37) | 2.88 (3.46) |
| Male | 3.39 (3.36) | 5.20 (3.43) | 2.13 (2.59) | 3.47 (3.08) | 4.04 (3.24) | 2.70 (3.41) |
| OCD and CTD | 3.16 (3.00) | 4.61 (3.29) | 1.98 (2.21) | 3.69 (3.54) | 3.69 (3.31) | 2.86 (3.71) |
| Female | 3.41 (3.40) | 5.14 (3.58) | 2.19 (2.48) | 4.14 (4.02) | 3.89 (3.36) | 2.59 (3.56) |
| Male | 2.96 (2.66) | 4.20 (3.01) | 1.80 (1.98) | 3.33 (3.10) | 3.52 (3.29) | 3.07 (3.85) |
| OCD without CTD | 4.09 (3.73) | 5.35 (3.36) | 2.09 (2.70) | 3.95 (3.33) | 4.40 (3.33) | 2.82 (3.42) |
| Female | 4.40 (3.82) | 5.35 (3.31) | 2.04 (2.71) | 4.18 (3.42) | 4.54 (3.37) | 2.90 (3.46) |
| Male | 3.46 (3.45) | 5.35 (3.47) | 2.18 (2.67) | 3.49 (3.08) | 4.12 (3.23) | 2.64 (3.34) |
| CTD without OCD | 1.55 (2.41) | 3.22 (2.95) | 2.27 (2.18) | 3.55 (3.05) | 2.47 (2.59) | 1.25 (2.13) |
| Female | 1.81 (2.34) | 3.71 (3.40) | 2.57 (2.54) | 4.55 (3.33) | 3.14 (2.93) | 1.88 (2.72) |
| Male | 1.41 (2.45) | 2.96 (2.68) | 2.12 (1.98) | 3.04 (2.78) | 2.12 (2.35) | 0.93 (1.68) |
CTD tourette disorder and related chronic tic disorders, OCD obsessive–compulsive disorder
The mean total OCI-R score for individuals with OCD and CTD was not significantly different from those with OCD without CTD (20.0 vs. 22.7; p value = 0.07; Table 3). Individuals with OCD and CTD had significantly lower Washing scores than individuals with OCD without CTD (3.16 vs. 4.09; p value < 0.01). The other subscales were not significantly different between these two groups.
We observed higher scores of Obsessing and Ordering in individuals with OCD and at least one additional psychiatric comorbidity compared to individuals without any psychiatric comorbidity (p value < 0.01; Table S1).
Discussion
In this study, for the first time, we demonstrate that the Swedish translation of the OCI-R has adequate psychometric properties. We found support for the six-factor structure of OCI-R: Washing, Obsessing, Hoarding, Ordering, Checking, and Neutralizing. To evaluate the internal consistency of the Swedish OCI-R, we estimated the Cronbach α value for individuals with OCD. Cronbach α value for the total score was 0.9, and between 0.85 and 0.9 for all the subscales. Cronbach’s α value of at least 0.70 has been suggested to indicate adequate internal consistency [31]. We calculated the generalizability coefficient and adjusted for the time differences between the latest diagnosis date and the date that the individuals completed the OCI-R. We did not observe a substantial change in the Cronbach α value before and after adjusting for the time differences. In general, the Cronbach α values of the Swedish translation of the OCI-R for the OCD cases, with and without adjustment for the time differences, were very similar to that of the original OCI-R by Foa et al. [11].
The OCI-R total score was slightly lower than the reported results in other similar studies (22.5 in this study vs. 25 in [30] and 30.1 in [20]). However, we showed that the time difference between the most recent diagnosis date and the date the individual completed the questionnaire, likely reflecting time in treatment, could explain the smaller estimates (22.5 before adjustment vs. 29.0 after adjustment).
A unique feature of the EGOS data is the availability of information about all comorbid psychiatric conditions. Eight percent of the individuals with OCD had a diagnosis of CTD. We did not observe a significant difference between total OCI-R scores for individuals with OCD and CTD and individuals with OCD without CTD; however, individuals with OCD and CTD had significantly lower Washing score than individuals with OCD without CTD. Multiple studies have shown that OCD patients without CTD score higher on washing/contamination scales [32–35].
We observed that 30% of individuals with OCD had an additional diagnosis of an anxiety disorder, and 25% also had major depressive disorder. Individuals with OCD and borderline personality disorder, and OCD and bipolar disorder had the highest OCI-R total score in comparison to other comorbidities. The severity of OCD was significantly higher in individuals with at least one psychiatric comorbidity than individuals with no psychiatric comorbidity. We conjecture that individuals with more severe symptoms carry a larger genetic load, which is the goal of our next study.
The present study had several strengths and some limitations: (1) we used data from the Swedish NPR, which created a genetically homogeneous sample and would be expected to minimize the risk of confounding due to population stratification; (2) all individuals had a clinical diagnosis of OCD by a specialist, which minimizes misdiagnosis; (3) a control group consisting of healthy individuals (individuals with no psychiatric diagnosis) was not available for this study. However, the data were available for a group of individuals with CTD without OCD. For this group, Cronbach’s α coefficient was close to the control populations reported by other studies [20]. Due to the genetic and phenotypic correlation of OCD and CTD, this group could not be treated as a control group, although the contrast between the results was informative; (4) another limitation of this study was the use of data from the NPR. While the NPR is considered a robust and reliable source for research, utilizing ICD diagnostic criteria, the register is lacking information about the individuals who do not seek clinical services at all or are treated at primary care. Hence, our sample may have over-represented more severe cases; (5) given the data collection protocol for this study, we were not able to test the Swedish translation of the OCI-R for convergent or divergent validity against other standardized rating scales for OCD.
Supplementary Material
Acknowledgements
We thank the EGOS families and clinicians for their participation. We appreciate Dr. Anna Grönberg and Dr. Sandra Bates for the Swedish translation of OCI-R and their support.
This study was supported by a grant from the Beatrice and Samuel A. Seaver Foundation (DEG, JDB, BM); the Mindworks Charitable Lead Trust (DEG); the Stanley Center for Psychiatric Research (DEG); NIMH R01MH124679 (DEG).
Footnotes
Conflict of interest The authors have no conflicts of interest to declare that are relevant to the content of this article.
Code availability We used the psych package developed by William Revelle in R version 3.6.0.
Declarations
Ethical approval Ethical approval was obtained from the Institutional Review Board at the Icahn School of Medicine at Mount Sinai, New York, USA, and the Regional Ethical Review Board in Stockholm, Sweden.
Consent to participate Informed consent was obtained from all individual participants included in the EGOS study.
Consent for publication Not applicable.
Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s00127-022-02231-z.
Availability of data and material
Study data are maintained at the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. Extracted DNA samples are stored at Karolinska Biobank [https://ki.se/en/research/ki-biobank]. Biological samples can be made available to approved researchers.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Study data are maintained at the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. Extracted DNA samples are stored at Karolinska Biobank [https://ki.se/en/research/ki-biobank]. Biological samples can be made available to approved researchers.