Autism spectrum disorders in the Stockholm Youth Cohort: design, prevalence and validity

Objective: Reports of rising prevalence of autism spectrum disorders (ASD), along with their profound personal and societal burden, emphasize the need of methodologically sound studies to explore their causes and consequences. We here present the design of a large intergenerational resource for ASD research, along with population-based prevalence estimates of ASD and their diagnostic validity. Method: The Stockholm Youth Cohort is a record-linkage study comprising all individuals aged 0–17 years, ever resident in Stockholm County in 2001–2007 (N = 589,114). ASD cases (N = 5,100) were identified using a multisource approach, involving registers covering all pathways to ASD diagnosis and care, and categorized according to co-morbid intellectual disability. Prospectively recorded information on potential determinants and consequences of ASD were retrieved from national and regional health and administrative registers. Case ascertainment was validated through case-note review, and cross validation with co-existing cases in a national twin study. Results: The 2007 year prevalence of ASD in all children and young people was 11.5 per 1,000 (95 % confidence interval 11.2–11.8), with a co-morbid intellectual disability recorded in 42.6 % (41.0–44.2) of cases. We found 96.0 % (92.0–98.4) o