Interpretation:With the exception of hyperactivity, the prevalence of symptoms of mental illness in Canadian children and adolescents has remained relatively stable from 1994/95 to 2008/09. Conflicting reports of escalating rates of mental illness in Canada may be explained by differing methodologies between studies, an increase in treatment-seeking behaviour, or changes in diagnostic criteria or practices.
AbstractResearch CMAJ, December 9, 2014, 186(18) E673
Methods
Study designThis study used data from the National Longitudinal Survey of Children and Youth, which involves a population-based cohort of Canadian children and adolescents followed prospectively every 2 years by Statistics Canada since 1994/95. 14 The cohort is considered nationally representative, with the exception of children living on First Nations reserves or Crown lands, in institutions and in some remote regions. This study was designed to collect information about multiple aspects of child health and development. The follow-up rate for the National Longitudinal Survey of Children and Youth from cycle 1 (1994/95) to cycle 8 (2008/2009) was 61%.15 Further details about the cohort, including study design and response rates (mostly above 80% at each wave), are described elsewhere. 14,15 The survey included numerous assessments related to child and adolescent mental health. The behaviour scale was adapted from questionnaires used in the Montreal Longitudinal Survey and the Ontario Child Health Study, which were designed to identify children who would most likely qualify for a psychiatric diagnosis based on symptom criteria for the revised 3rd edition of the Diagnostic and Statistical Manual of Mental Disorders. 16 This scale has been used in previous studies of child and adolescent adjustment, and has shown good psychometric properties. 17,18 In each cycle, participants aged 10 years or older were asked to self-report the frequency of various feelings and behaviours in the past week, with 3 possible responses ranging from "never or not true" to "often or very true." Each item was assigned a score of 0 to 2 (higher scores indicating a greater degree of mental health problems). Questionnaires were completed on paper, at home in a private setting, and sealed in envelopes to ensure confidentiality.Composite scores were created by summing item scores on each of 4 subscales relevant to adolescent mental illness: conduct disorder (6 items, e.g., "I kick or hit other people my age"), hyperactivity (7 items, e.g., "I am impulsive, I act without thinking"), indirect aggression (5 items, e.g., "When I am mad at someone, I say bad things behind his/her back"), and symptoms of depression/anxiety (7 items, e.g., "I am not as happy as other people my age" and "I worry a lot"). 19 The same items were collected at each cycle, with the exception of 1 hyperactivity item and 1 depression/anxiety item, which were dropped in cycle 4. In the interest of comparability over time, these items were not included in composite scores. All items comprising the final scale...