Tracking the course of depressive and anxiety symptoms across adolescence (the CATS study): a population-based cohort study in Australia.

Background: Adolescent mental health appears to be in crisis, yet few studies have comprehensively charted the course of common mental disorders (CMDs; depression and anxiety) across this key life stage. We aimed to describe the course of CMD symptoms in adolescence by summarising annual prevalence, cumulative incidence, and course for depression and anxiety, both separately and as comorbid CMDs, by sex assigned at birth in a contemporary Australian cohort.
Methods: The Child to Adult Transition Study (CATS) was established in 2012 to form a representative cohort of adolescents in Melbourne, VIC, Australia. 43 schools were recruited using a stratified sampling approach, and all 2289 students aged 8-9 years were invited to participate. 1239 (54·1%) students obtained parental written informed consent and were followed up annually from 2012 to 2019 for a total of ten waves. Data from waves 3-10 (ages 10 to 18 years) were used for the current study and analysed to describe the course of symptoms of CMDs across adolescence. Primary measures of interest were clinically relevant depressive symptoms, clinically relevant anxiety symptoms, and any CMD (clinically relevant depressive or anxiety symptoms) at waves 3-10. A secondary measure of interest was comorbid CMDs (concurrent reporting of clinically significant anxiety and depressive symptoms) at waves 3-10. Depressive symptoms in the past 2 weeks were self-reported using the 13-item validated Short Mood and Feelings Questionnaire (SMFQ) at each wave, with a threshold score of 12 or more indicating clinically relevant symptoms. Anxiety symptoms in the past two weeks were self-reported using an 8-item shortened version of the Spence Children's Anxiety Scale (SCAS) at each wave, with a threshold score of 11 or higher indicating clinically relevant symptoms. The course of CMDs was described using annual prevalence, cumulative incidence for depression and anxiety, separately and combined. Missing data were handled via multiple imputation. An author with lived experience was involved in the research and writing process.
Findings: Of the 1239 adolescents who participated in the study, 667 (53·8%) were female and 572 (46·2%) were male. 769 (62·1%) of 1239 were classified as socioeconomically advantaged, 675 (66·4%) of the 1016 with available data had a mother whose highest level of education was vocational or tertiary, and 579 (70·7%) of the 819 participants with ethnicity data identified as Anglo-Celtic or European. Overall, incidence of any clinically significant CMD symptoms during adolescence was 74% (95% CI 70-77; 84% [81-88] for females and 61% [55-66] for males). Independently, incidences of clinically significant depressive symptoms and anxiety symptoms were 65% (62-68) and 58% (55-62), respectively. Incidence of comorbid CMD was 48% (45-52). The estimated mean ages of first report in adolescence for both sexes were 14·1 years (95% CI 13·9-14·4) and 13·6 years (3·3-13·9) for depressive and anxiety symptoms, respectively. Of those who reached the threshold score for any CMD between ages 10 and 18 years, over half had a chronic (three or more waves) course (depression 54% [49-60]; anxiety 52% [47-58]), and a third met criteria for full remission at any subsequent wave (depression 30% [25-35]; anxiety 33% [27-39]). Females were consistently estimated to have a worse course of adolescent CMDs compared with males (eg, 64% [58-70] of females had a chronic course of depressive symptoms vs 37% [26-48] of males).
Interpretation: In this contemporary multi-wave cohort study, almost three-quarters of adolescents reported CMD symptoms. The likelihood of chronicity of CMD symptoms (ie, recurrence) was high. Universal responses are urgently required to address this considerable public health problem.
Funding: National Health and Medical Research Council of Australia and the Royal Children's Hospital Foundation.
Competing Interests: Declaration of interests SMS and GCP were supported by the National Health and Medical Research Council of Australia (NHMRC) Investigator Grant (GNT1196999). SGD was supported by an NHMRC Investigator Grant (GNT202171). MM-B was supported by an NHMRC Investigator Grant (GNT 2009572). All other authors declare no competing interests.
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