CONTEMPORARY MEASURES OF MENTAL HEALTH STATUS AND SCHOOL-BASED RELATIVE AGE EFFECTS IN CANADIAN ADOLESCENTS
This thesis is on the epidemiology of relative age effects and how they relate to the mental health status of young people. Contemporary measures of mental health are developed, and the association between school-based relative age and mental health is investigated. It consists of four manuscripts, a proposed conceptual model, and a literature review. The analyses used data from the 2014 Canadian Health Behaviour in School-aged Children study. The first manuscript (BMJ Open) developed a categorical measure of mental health status inspired by the Dual-factor Model, by combining information on subjective well-being and psychopathology. Mental health status was significantly associated with indicators of social and academic functioning, and mental health. Findings support construct validity. The second manuscript (SSM–Population Health) developed and tested a novel continuous measure of mental health, based on our adaptation of the Dual-factor Model. The continuous version has conceptual and statistical advantages over the categorical form, and evidence supports it as construct valid. A supplementary chapter provides background information on relative age effects, a review of studies on school-based relative age and adolescent mental health, and a conceptual model linking relative age at school entry to adolescent mental health. The third manuscript examined the association between school-based relative age and mental health in Canadian adolescents. Analyses were stratified by sex, and effect modification by grade group was considered. Younger students were at increased risk of poor mental health, but effect sizes were modest, and inconsistent depending on the indicator examined. The fourth manuscript examined effect modification in the association between relative age and suboptimal mental health by levels of family affluence and social supports. There was minimal evidence of statistically significant effect modification, but the effects of relative age were less pronounced in groups of students reporting lower levels of support and lower relative family affluence. Following this manuscript is a review of potential strategies that have been suggested for addressing school-based relative age effects. There is a need for studies assessing their effectiveness.