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Introduction Research suggests that there is often a high degree of missingness in youth body mass index (BMI) data derived from self-reported measures, which may have a large effect on research findings. The first step in handling missing data is to examine the levels and patterns of missingness. However, previous studies examiningyouth BMI missingness used logistic regression, which is limited in its ability to discern subgroups or identify a hierarchy of importance for variables, aspects that may go a long way in helping understand missing data patterns. Methods This study used sex-stratified classification and regression tree (CART) models to examine missingness in height, body mass and BMI data among 74 501 youth participating in the 2018/19 COMPASS study (a prospective cohort study examining health behaviours among Canadian youth), where 31% of BMI data were missing. Diet, movement, academic, mental health and substance use variables were examined for associations with missingness in height, body mass and BMI. Results CART models indicated that the combination of being younger, having a selfperception of being overweight, being less physically active and having poorer mental health yielded female and male subgroups highly likely to be missing BMI values. Survey respondents who did not perceive themselves as overweight and who were older were unlikely to be missing BMI values. Conclusion The subgroups identified by the CART models indicate that a sample that deletes cases with missing BMI would be biased towards physically, emotionally and mentally healthier youth. Given the ability of CART models to identify these subgroups and a hierarchy of variable importance, they are an invaluable tool for examining missing data patterns and appropriate handling of missing data.

Purpose We investigated whether social health mitigates the association between weight perception and anxiety and depression 1 year later in a large sample of Canadian youth in a prospective, gender-specific analysis. Methods We used 2 years of linked survey data from 20,485 grade 9–11 students who participated in wave 6 (2017/18) and 7 (2018/19) of the COMPASS study. Mental health outcomes included the Generalized Anxiety Disorder—7 item (GAD-7) scale and the 10-item Centre for Epidemiological Studies Depression Scale Revised (CESD-10-R). Social health encompassed students’ perceived relationships with friends, family, teachers, and within schools. Multilevel, prospective, linear models regressed mental health (at wave 7) on social health (at wave 6) and weight perception (at wave 6) while controlling for weight status, ethnicity, and grade (at wave 6). Interaction terms were used to test social health factors as moderators in the association between weight perception and mental health. Results Overweight perceptions were associated with higher anxiety and depression scores among youth; this was more pronounced among females. Social health was associated with lower anxiety and depression scores. Among females only, an overweight perception had the highest predicted scores for significant depressive symptoms. Among males only, underweight perceptions were associated with higher anxiety scores. No social health factors had moderating effects in females, and only two interactions were significant among males: feeling safe at school had protective associations with anxiety scores among those with underweight perceptions while those with overweight perceptions had higher depression scores when they reported rewarding social relationships. Conclusion Overweight perceptions in all youth, and underweight perceptions in males, predicted anxiety and depression symptoms 1 year later. The role of social health should not be discounted as a means of preventing anxiety and depression in youth, although this study suggests it is not sufficient to protect against adverse associations with overweight perceptions for all youth, and underweight perceptions for males. Supplementary Information The online version contains supplementary material available at 10.1007/s00127-022-02219-9.

Supplementary Material 1

Substance use behaviours have been found to cluster in youth, and cannabis use has been previously linked to tobacco and e-cigarette use. The objective of the current study was to examine the bidirectional associations between cannabis, e-cigarette, and cigarette use among a large sample of Canadian secondary school students. A sample of students in grades 9–11 (n = 14,652) from Ontario and Alberta, Canada who participated in two waves of the COMPASS Study (Time 1 (T1): 2015–2016; Time 2 (T2): 2016–2017) was identified. Autoregressive cross-lagged models investigated the stability of product use between T1 and T2, as well as the bidirectional associations between current cannabis, e-cigarette, and cigarette use while controlling for demographic covariates. Significant autoregressive and bidirectional associations between all three substances were observed. Students who reported using cigarettes and e-cigarettes at T1 were more likely to report using cannabis at T2. Similarly, students who reported using cannabis at T1 were more likely to report using cigarettes and e-cigarettes at T2. Given the bidirectional associations identified between cannabis, e-cigarette, and cigarette use in this research, continued monitoring of evolving policies related to cannabis and e-cigarette use in Canada is needed. Additionally, school and community-based prevention efforts targeting youth should consider addressing poly-substance use.

Additional file 1: Supplemental Table 1. Results of the ordinal regression models that regressed mental health (low versus medium/high) on hunger, social support factors and control variables, among youth in Canada in gender-specific analyses. The point estimates are adjusted odds ratios and the intervals show 95% confidence intervals

Supplemental Material, DS_10.1177_0706743718809340 for Traffic Violations among Young People with Attention-Deficit Hyperactivity Disorder by Mark A. Ferro, and Scott T. Leatherdale in The Canadian Journal of Psychiatry

Search results â Targeted web searches. This table depicts the ten unique searches applied to Google search engine and the number of records identified from each search.

Search results â Custom Google search engines. This table depicts the ten unique searches applied to the custom Google search engines examined, the number of results each search yielded within each search engine, and the number of records identified from each search.

Background: To examine if the recommended taxonomies for the stages of youth smoking onset are aligned with the beliefs of smoking youth. Methods: The SHAPES Tobacco Module was administered to 23,047 students (grades 9 to 13) in a convenience sample of 29 secondary schools during the 2000–2001 school year in the province of Ontario, Canada. Cross-tabs were used to compare a student’s selfperceived smoking status to their smoking status as determined with the currently recommended stage taxonomies for smoking behaviour. Results: The majority of students classified as regular smokers (52.4%) and experimental smokers (98.9%) did not actually consider themselves to be smokers. Self-reported smoking status appeared to be relatively consistent for the never smoker and established smoker categories. Conclusions: Additional research is required to develop stage taxonomies that are aligned with the self-perceptions of non-established youth smokers.

Changes in the number of types of beverages available in vending machines within participating COMPASS secondary schools (n = 78) within three policy groups: Alberta (n = 9), Ontario – Public (n = 64), and Ontario – Private (n = 5). (DOCX 53 kb)

Changes in the number of types of beverages available in vending machines within participating COMPASS secondary schools (n = 78) within three policy groups: Alberta (n = 9), Ontario – Public (n = 64), and Ontario – Private (n = 5). (DOCX 53 kb)

Additional file 1: Supplementary Table A. Logistic regression model predicting likelihood of missing outcome data among adolescents who participated in the 2017–18 and 2018–19 school years of the COMPASS Study in Alberta, British Columbia, Ontario, and Quebec.

Additional file 1: Supplementary Table A. Logistic regression model predicting likelihood of missing outcome data among adolescents who participated in the 2017–18 and 2018–19 school years of the COMPASS Study in Alberta, British Columbia, Ontario, and Quebec.