Table 1.

Summary of Cross-Sectional Studies.

	Sample			Measures		Results		Additional Characteristics
Author, Country	Type	N (% Males/Boys)	Age Range; M (SD); Type	Loneliness Measure	Well-Being Measure(s)	Loneliness M (SD) or N (%)	Association between Loneliness and Well-Being	Data Collection Timing/School Closure	Qual (/9)
Boursier et al. [31], Italy	Com	544 (28.1)	13–20; 16.22 (1.83); Adol	Italian Loneliness Scale-self-report	Depression subscale of Depression-Anxiety Stress Scale-21 Multidimensional Assessment of COVID-19 related fears -self-report	2.11 (0.6) Min = 1 Max = 4	Dep: r = 0.564, p < 0.001 Loneliness→Depression β = 0.721, se = 0.054, p < 0.001 COVID-19 Anx: r = 0.294, p < 0.001 COVID-19 Anx→Loneliness β = 0.198, se = 0.302, p < 0.001	January–March 2021, school closure unclear	6
Cauberghe et al. [29], Belgium	Com	2165 (34.4)	13–19; 15.51 (1.59); Adol	Revised UCLA Loneliness Scale-6 items-self-report	General Anxiety Disorder Scale-7 Center of Epidemiological Studies Depression Scale -self-report	Boys: 2.62 (0.76) Girls: 2.92 (0.77)	Anx: r = 0.523, p < 0.01 Happiness (vs. Depression): r = −0.590, p < 0.01 Loneliness→Happiness β = −0.616, p < 0.01	16–30 April 2020, during school closure	6
Dondi et al. [32], Italy	Both	6210 (NA)	Up to age 18; NA; Both	Single item of child feeling lonely-parent-report	Single items from Sleep Disturbance Scale for Children -difficulty falling asleep (sleep disorder) -maintaining sleep -nightmares -parent-report	No: 32.4% Yes, not putting it into words: 31.6% Yes, putting it into words: 36.0%	Loneliness→Sleep Falling asleep: -Yes not putting into words: OR: 1.85 (se = 0.14) -Yes putting into words: OR: 1.97 (se = 0.15) Staying Asleep: -Yes not putting into words: OR: 1.83 (se = 0.16) -Yes putting into words: OR: 2.11 (se = 0.18) Nightmares: -Yes not putting into words: OR: 2.10 (se = 0.21) -Yes putting into words: OR: 2.05 (se = 0.20) p < 0.01 for all	1 September–15 October 2020, school closure unclear	5
Dubois-Comtois et al. [33], Canada	Com	144 (51.4)	9–12; 10.44 (1.09); Both	Negative Experienced Aloneness Scale of the Loneliness and Aloneness Scale for Children and Adolescents-self-report	Fear of COVID-19 Scale (anxiety toward COVID-19)-self-report Child Behavior Checklist (externalizing)-parent-report Youth-Self Report (internalizing)-self-report	33.65 (6.88) Min = 12 Max = 48	Aversion to Aloneness and: Internalizing: r = 0.35, p < 0.001 Loneliness→Internalizing b = 0.27, se = 0.08, β = 0.26, p = 0.001, 95% CI [0.11, 0.43] Externalizing: r = 0.17, p < 0.05 Loneliness→Externalizing b = 0.02, se = 0.08, β = 0.002, p = 0.82, 95% CI [−0.14, 0.18] COVID-19 Anx: r = 0.32, p < 0.001 Loneliness→COVID-19 Anx b = 0.22, se = 0.07, β = 0.26, p = 0.002, 95% CI [0.08, 0.35]	18 April–18 May 2020, during school closure	5
Ellis et al. [34], Canada	Com	1054 (21.9)	14–18; 16.68 (0.78); Adol	Revised UCLA Loneliness Scale-self-report	Brief Symptom Inventory-self-report	Boys: 2.26 (se = 0.15) Girls: 2.85 (se = 0.06) Min = 1 Max = 4	Dep: r = 0.53, p < 0.01	4–16 April 2020, during school closure	6
Espinoza and Hernandez [35], US	Com	993 (41)	14–18; 16.09 (1.24); Adol	Items adapted from Asher and Wheeler Loneliness Scale-self-report	Center for Epidemiologic Studies Depression Scale-self-report	2.56 (1.03) Min = 1 Max =5	Dep: r = 0.61, p < 0.001	15 April–May 2020; school closure unclear	6
Fernandes et al. [36], Brazil	Com	343 (44.3)	14–18; 16.1 (0.9); Adol	COVID-19 related measure with social isolation item-self-report	Children’s Depression Inventory-self-report	Social Isolation: -Extremely isolated: 8.5% -Very isolated: 20.1% -Moderately isolated: 41.4% -Slightly isolated: 19.8% -Not at all: 10.2%	Isolation (vs. No Isolation)→Dep (vs. No Dep) PR (Prevalence Ratio): 2.04, 95% CI [1.00–4.14]	April–July 2021, school closure unclear	6
Fogarty et al. [37], Australia	Com	257 (45.5)	14–17; 15.7 (0.87); Adol	COVID-19 CRISIS Tool, single item on feeling lonely -self-report Scale of 0–4 dichotomized: 0–1 = 0, 2–4 = 1	Patient Health Questionnaire-Adolescent The Generalised Anxiety Disorder Scale-7 -self-report	38.7% said moderately to extremely lonely	Dep: r = 0.56, p < 0.001 Loneliness→Dep β = 0.31, b = 3.88, 95% CI [2.61, 5.15], p < 0.001 Anxiety: r = 0.44, p < 0.001 Loneliness→Anx β = 0.16, b = 1.44, 95% CI [0.44, 2.43], p = 0.005	July–September 2022 (during second lockdown), during school closure	7
Gilsbach et al. [38], Germany	Both	195 147 Clinical Group with Diagnosed Mental Disorder (43.6) 48 Non-Clinical (66.7)	6–18; Clinical: 13.3 (3.0) Non-Clinical: 13.5 (3.0); Both	Single item on impact of COVID-19 on loneliness -parent-report -self-report	NA; compared clinical to non-clinical sample	M (SD) NA Min = −2 (not at all) Max = 2 (very much)	Mean difference in Loneliness between Clinical and Non-Clinical samples: -Self-report: F(1, 137) = 0.25, p = 0.62 -Parent-report: F(1, 116) = 1.71, p = 0.19	Spring 2020, school closure unclear	6
Hou et al. [39], China	Com	826 (57.1)	Senior high school up to 18; NA; Adol	UCLA Loneliness Scale-self-report	Patient Health Questionnaire-9-self-report	47.92 (8.55) Min = 0 Max = 60	Dep: r = 0.425, p < 0.001 Loneliness→Dep β = 0.337, p < 0.001,	April–May 2020, school closure unclear	7
Jones et al. [40], US	Com	7705 (49.6)	Grades 9 to 12; NA; Adol	Single item about feeling close to persons at school-self-report	Single items: -how often mental health not good during pandemic -how often mental health not good during last 30 days -considering suicide past 12 months -attempt suicide past 12 months -self-report	Agree, felt close: 46.6%Not sure or disagree: 53.4%	Overall: Compared to students who did not feel close to persons at school, students who felt close: -Lower prevalence of poor mental health during pandemic: 28.4% vs. 45.2% -Lower prevalence of poor mental health last 30 days: 23.5% vs. 37.8% -Lower prevalence of having seriously considered suicide: 14.0% vs. 25.6% -Lower prevalence of having attempted suicide: 5.8% vs. 11.9% p < 0.05 for all	January–June 2021, school closure unclear	5
Kayaoğlu and Başcıllar [41], Turkey	Com	423 (36.4)	10–19; 15.23 (2.23); Adol	UCLA Loneliness Scale-short form-self-report	Children’s Depression Inventory-self-report	16.43 (4.93) Min = 7 Max = 52	Dep: r = 0.084, p = 0.03	Not provided, but during the COVID-19 Pandemic	8
Kilinçel and Muratdagi [42], Turkey	Com	1142 (63.2)	12–18; 15.6 (2.8); Adol	UCLA Loneliness Scale-self-report	State-Trait Anxiety Inventory-self-report Social Media Disorder Scale-self-report	NA	State Anx: r = 0.380, p < 0.01 Social Media Disorder: r = 0.093, p < 0.01 Loneliness→Social Media Disorder β = 0.150, p = 0.001	29–30 March 2022, online school assessed	5
Laslo-Roth et al. [43], Israel	Both	280; ADH-D: 166 (71) No ADH-D: 114 (57)	NA; ADHD: 9.33 (2.45) No ADHD: 9.89 (2.2); Child	Single item of child seeming to be lonely-parent-report	ADHD diagnosis	2.71 (1.27) Min = 1 Max = 5	ADHD status→Loneliness Step 1: β = 0.22, p < 0.01 Step 2: β = 0.05, NS	During COVID-19 pandemic but details not provided, school closure unclear	6
Li et al. [44], Australia	Com	760 (28)	12–18; 14.8 (1.26); Adol	Single item from UCLA Loneliness Scale-self-report	Asked if previously diagnosed with anxiety and/or depression Warwick Edinburgh Mental Well-Being Scale short-form Body Preoccupation Scale of the Illness Attitude Scales -self-report	Frequency of feeling alone: -Hardly ever: 17.1% -Some of the time: 30.7% -Often: 51.4%	Mean Loneliness by Diagnosis vs. No Diagnosis: t(663) = −5.61, p < 0.01 -Diagnosis: M = 5.63, SD = 2.30 -No Diagnosis: M = 4.56, SD = 2.44 Loneliness and: Health Anx: r = 0.20, p < 0.01 Overall Well-Being: r = −0.59, p < 0.01	2 June–5 August 2020, during school closure	4
Li et al. [45], China	Com	1034 (61.2)	12–19; 15.76 (1.20); Adol	UCLA Loneliness Scale-self-report	Mobile Phone Addiction Index-self-report	44.88 (10.19) Min = 20 Max = 100	Mobile Addiction: r = 0.14, p < 0.001 β = 0.14 se = 0.03, p < 0.001,	22–29 May 2020, school closure unclear	7
Liu et al. [46], China	Com	1594 (49.4)	9–16; 13.13 (1.54); Both	Loneliness and Aloneness Scale for Children and Adolescents -Peer loneliness -Family Loneliness-self-report	Center for Epidemiologic Studies Depression Scale for Children-self-report	-Peer Loneliness: 1.32 (0.46) -Family Loneliness: 1.78 (0.68) Min = 1 Max = 4	Peer loneliness and dep: r = 0.49, p < 0.001 Family loneliness and dep: r = 0.58, p < 0.001	April 2020, school closure unclear	6
Low and Mounts [47], US	Com	272 (NA)	12–18; NA; Adol	UCLA Loneliness Questionnaire—parent-report	Revised Child Anxiety and Depression Scale-parent-report	0.95 (0.73) Min = 0 Max = 3	Internalizing: r = 0.90, p < 0.01	June–November 2020, during school closure	6
Murata et al. [48], US	Com	583 (20)	NA; 15.80 (1.40); Adol	Feelings of loneliness since the COVID-19 pandemic-self-report	Patient Health Questionnaire Generalized Anxiety Disorder (GAD-7) -self-report	6.9 (2.3) Min = 1 Max = 10	Loneliness→Dep: β = 0.376, 98% CI [0.24, 0.52], p < 0.001, Loneliness→Anx: β = 0.57, 98%CI [0.41, 0.74], p < 0.001,	27 April–13 July 2020; school closure unclear	5
Oosterhoff et al. [49], US	Com	683 (22.7)	13–18; 16.35 (1.13); Adol	Interpersonal Needs Questionnaire (Belongingness)-self-report	Patient-Reported Outcomes Measurement Information-short-fixed-form -Depression scale -Anxiety scale -self-report	4.21 (1.49) Min = 1 Max = 7	Dep: r = −0.45, p < 0.05 (depression related to higher belongingness) Anx: r = −0.21, p < 0.05 (anxiety related to higher belongingness)	29–30 March 2022; school closure unclear	7
Palmer et al. [50], US	Com	459 (18.7)	13–18; 16.24 (1.26); Adol	Single item on how lonely from Positive and Negative Affect Schedule-X-self-report	Positive and Negative Affect Schedule-for children UCLA Post-Traumatic Stress-Reaction Index Pittsburgh Sleep Quality Index National Sleep Foundation Sleep Diary Consensus Sleep Diary Single item on bad dreams -self-report	2.82 (1.36) Min = 1 Max = 5	Internalizing: Positive Affect: r = −0.33, p < 0.01 Negative Affect: r = 0.63, p < 0.01 Others: Post-Traumatic Stress-Symptoms: r = 0.61, p < 0.01 Nightmares: r = 0.12, p < 0.01 Sleep onset: r = 0.17, p < 0.01 Sleep quality: r = 0.21, p < 0.01	1–5 April 2020, during school closure	7
Pan et al. [51], China	Com	5783 (60.75)	NA; NA; Adol	UCLA Loneliness Questionnaire-self-report	Mental Health of Middle School Students-self-report (higher scores mean worse mental health)	42.77 (8.75) Min = 20 Max = 80	Overall Mental Health: r = 0.578, p < 0.01 Loneliness→Overall Mental Health β = 0.036, p < 0.001	May 2020, during school closure	4
Pfetsch et al. [52], Germany	Com	205 (43)	14–19; 15.83 (1.44); Adol	UCLA-Revised (10 items) subscales: -feelings of isolation -lack of proximity -self-report	Short Warwick-Edinburgh Mental Well-Being Scale-self-report	NA	Overall Well-Being: -Loneliness isolation: r = −0.67, p < 0.001 Isolation→Well-being Model 3: b = −0.21, se = 0.07, β = −0.28, p < 0.001 Model 4: b = −0.20, se = 0.07, β = −0.26, p < 0.01 -Loneliness proximity: r = −0.52, p < 0.001 Proximity→Well-being Model 3: b = −0.10, se = 0.07, β = −0.10, p > 0.05 Model 4: b = −0.09, se = 0.07, β = −0.10, p > 0.05	Middle of March–beginning April 2021, during school closure	7
Sette et al. [53], Italy	Com	748 (48.3)	7–11; 8.91 (1.07); Child	Loneliness and Social Dissatisfaction Questionnaire-self-report	Children’s Depression Inventory Social Anxiety Scale for Children-Revised -self-report	1.47 (0.67) Min = 1 Max = 5	Dep: r = 0.65, p < 0.001 Social Anx: r = 0.52, p < 0.001	December 2020–April 2021, both school closure and reopened assessed	7
Sette et al. [54], Italy, Spain, UK	Com	236 (44.49)	6–12; 9.25 (1.2); Child	Adapted from Asher et al.-self-report	The Children’s Depression Inventory-Short Form Spence Children’s Anxiety Scale (SCAS-Child)-self-report	1.57 (0.57) Min = 1 Max = 5	Dep: r = 0.62, p < 0.001 Anx: r = 0.41, p < 0.001	23 April–25 June 2020, during school closure	6
Soneson et al. [55], UK	Com	16,940 (38.9)	8 to 18; NA; Both	-General loneliness (reference) -Change in loneliness during lockdown -self-report	Single item on mental well-being	NA	General Loneliness (Never, Sometimes, Often) by Mental Well-Being (Worse, Same, Better) -Never and worse: 22.8% -Never and same: 61.0% -Never and better: 61.3% -Sometime and worse: 47.5% -Sometimes and same: 31.9% -Sometimes and better: 32.2% -Often and worse: 30.0% -Often and same: 7.2% -Often and better: 6.5% Change in Loneliness (Much Less, Slightly Less, Same, Slightly More, Much More) by Mental Well-Being (Worse, Same, Better) -Much less and worse: 5.7% -Much less and same: 9.3% -Much less and better: 23.7% -Slightly less and worse: 11.7% -Slightly less and same: 14.1% -Slightly less and better: 21.0% -Same and worse: 24.4% -Same and same: 55.2% -Same and better: 34.7% -Slightly more and worse: 42.2% -Slightly more and same: 18.7% -Slightly more and better: 18.1% -Much more and worse: 16.0% -Much more and same: 2.7% -Much more and better: 2.5%	May–July 2020, both school closure and reopened assessed	4
Varela et al. [56], Chile	Com	2370 (18.27) total but only subsample 15–18	15–18; NA; Adol	Single item on fear of loneliness-self-report	Patient Health Questionnaire-9-self-report	N/A Min = 0 Max = 3	Fear of Loneliness→Dep Dep: b = 3.790 [4.358], se = (0.196, [0.161]), p < 0.001 (brackets = weighted values)	December 2020, school closure unclear	8
Wang et al. [57], China	Com	6587 (49.9)	NA; 15.50 (1.70); Adol	Single item on loneliness from Children’s Depression Inventory-self-report	Strengths and Difficulties Questionnaire-self-report	No: 66.1% Yes = 33.9%Min = Never Max = Many times or always	Overall Well-Being: (higher difficulties) Loneliness→Difficulties Model 1: b = 5.41, se = 0.25, β = 0.45, p < 0.001 Model 2: b = 5.95, se = 0.20, β = 0.50, p < 0.001 Model 3: b = 6.23, se = 0.18, β = 0.52, p < 0.001	16 April–14 May 2020, during school closure	5
Yilmaz et al. [58], Turkey	Com	3655 (39.4)	Grade 6 to 11; NA; Adol	Developed a scale that included Loneliness Subscale-self-report (4 items)	Developed a scale that included Anxiety Subscale-self-report (4 items)	2.96 (1.19) Min = 1 Max = 5	Anx: r = 0.353, p < 0.001	June 2020, during school closure	4
Zhu et al. [59], Hong Kong	Com	1346 (47.3)	8–17; 12.6 (1.32); Both	Single item about feeling lonely-self-report	Game Addiction Scale-self-report	0.52 (0.87) Min = 0 Max = 3	Loneliness→Game Addiction Primary Students: -Excessive Game Addiction: aOR: 0.71, 95% CI [0.65–0.78], p < 0.001 -Pathological Game Addiction: aOR: 0.94, 95%CI [0.80, 1.12], p > 0.05 Secondary Students: -Excessive Game Addiction: aOR: 1.00, 95%CI [0.95–1.05], p > 0.05 -Pathological Game Addiction: aOR: 0.88, 95% CI [0.9–0.99], p < 0.01.	June 2020, schools reopened	6

Note. When multiple statistics were reported for results, either the main univariate/multivariate results are reported or a summary description of the main pattern of results are reported; NA = Not Applicable or Not Provided; Both (under sample type) = Both community and clinical sample; Com = Community sample; Adol = Adolescent sample; Child = Child sample; Both (under sample age) = Both child and adolescent sample; Min = Minimum score; Max = Maximum score; Dep = Depression Symptoms; Anx = Anxiety Symptoms; Internalizing = Internalizing Symptoms; Externalizing = Externalizing Symptoms; ADHD = Attention Deficit Hyperactivity Disorder; Qual = Quality Rating.