From 2019... Greater male cognitive variability has implications for both tails of the distribution: Danish data (n = 1.3 million) finds that twice as many boys than girls are diagnosed with intellectual disability

From 2019... Incidence Rates and Cumulative Incidences of the Full Spectrum of Diagnosed Mental Disorders in Childhood and Adolescence. Søren Dalsgaard et al. JAMA Psychiatry. 2020;77(2):155-164. Nov 20, 2019, doi:10.1001/jamapsychia

Key Points

Question  What are the age- and sex-specific incidence rates and cumulative incidences of the full spectrum of diagnosed mental disorders during childhood and adolescence?

Findings  In this nationwide cohort study of 1.3 million individuals in Denmark, the risk (cumulative incidence) of being diagnosed with a mental disorder before 18 years of age was 14.63% in girls and 15.51% in boys. Distinct age- and sex-specific patterns of occurrence were found across mental disorders in children and adolescents.

Meaning  These findings suggest that precise estimates of rates and risks of all mental disorders during childhood and adolescence are essential for future planning of services and care and for etiological research.

Abstract

Importance: Knowledge about the epidemiology of mental disorders in children and adolescents is essential for research and planning of health services. Surveys can provide prevalence rates, whereas population-based registers are instrumental to obtain precise estimates of incidence rates and risks.

Objective  To estimate age- and sex-specific incidence rates and risks of being diagnosed with any mental disorder during childhood and adolescence.

Design  This cohort study included all individuals born in Denmark from January 1, 1995, through December 31, 2016 (1.3 million), and followed up from birth until December 31, 2016, or the date of death, emigration, disappearance, or diagnosis of 1 of the mental disorders examined (14.4 million person-years of follow-up). Data were analyzed from September 14, 2018, through June 11, 2019.

Exposures: Age and sex.

Main Outcomes and Measures  Incidence rates and cumulative incidences of all mental disorders according to the ICD-10 Classification of Mental and Behavioral Disorders: Diagnostic Criteria for Research, diagnosed before 18 years of age during the study period.

Results  A total of 99 926 individuals (15.01%; 95% CI, 14.98%-15.17%), including 41 350 girls (14.63%; 95% CI, 14.48%-14.77%) and 58 576 boys (15.51%; 95% CI, 15.18%-15.84%), were diagnosed with a mental disorder before 18 years of age. Anxiety disorder was the most common diagnosis in girls (7.85%; 95% CI, 7.74%-7.97%); attention-deficit/hyperactivity disorder (ADHD) was the most common in boys (5.90%; 95% CI, 5.76%-6.03%). Girls had a higher risk than boys of schizophrenia (0.76% [95% CI, 0.72%-0.80%] vs 0.48% [95% CI, 0.39%-0.59%]), obsessive-compulsive disorder (0.96% [95% CI, 0.92%-1.00%] vs 0.63% [95% CI, 0.56%-0.72%]), and mood disorders (2.54% [95% CI, 2.47%-2.61%] vs 1.10% [95% CI, 0.84%-1.21%]). Incidence peaked earlier in boys than girls in ADHD (8 vs 17 years of age), intellectual disability (5 vs 14 years of age), and other developmental disorders (5 vs 16 years of age). The overall risk of being diagnosed with a mental disorder before 6 years of age was 2.13% (95% CI, 2.11%-2.16%) and was higher in boys (2.78% [95% CI, 2.44%-3.15%]) than in girls (1.45% [95% CI, 1.42%-1.49%]).

Conclusions and Relevance  This nationwide population-based cohort study provides a first comprehensive assessment of the incidence and risks of mental disorders in childhood and adolescence. By 18 years of age, 15.01% of children and adolescents in this study were diagnosed with a mental disorder. The incidence of several neurodevelopmental disorders peaked in late adolescence in girls, suggesting possible delayed detection. The distinct signatures of the different mental disorders with respect to sex and age may have important implications for service planning and etiological research.

Check also Greater male variability is currently universal in internationally comparable assessments; some of this heterogeneity can be attributed to some species universal mechanism or some other social/cultural phenomenon

Sex differences in variability across nations in reading, mathematics and science: a meta-analytic extension of Baye and Monseur (2016). Helen Gray, Andrew Lyth, Catherine McKenna, Susan Stothard, Peter Tymms and Lee Copping. Large-scale Assessments in EducationAn IEA-ETS Research Institute Journal 20197:2. https://www.bipartisanalliance.com/2019/03/greater-male-variability-is-currently.html