Relative age within the school year and diagnosis of attention-deficit hyperactivity disorder: a nationwide population-based study

Publication date: Available online 9 October 2017 Source:The Lancet Psychiatry Author(s): Kapil Sayal, Roshan Chudal, Susanna Hinkka-Yli-Salomäki, Petteri Joelsson, Andre Sourander Background Findings are mixed on the relationship between attention-deficit hyperactivity disorder (ADHD) and younger relative age in the school year. We aimed to investigate whether relative age is associated with ADHD diagnosis in a country where prescribing rates are low and whether any such association has changed over time or relates to comorbid disorders (eg, conduct disorder [CD], oppositional defiant disorder [ODD], or learning disorder [LD]). Methods We used nationwide population-based registers to identify all Finnish children born between Jan 1, 1991, and Dec 31, 2004, who were diagnosed with ADHD from age 7 years onwards (age of starting school). We calculated incidence ratios to assess the inter-relations between relative age within the school year, age at ADHD diagnosis, and year of diagnosis (1998–2003 vs 2004–11). Findings Between Jan 1, 1998, and Dec 31, 2011, 6136 children with ADHD were identified. Compared with the oldest children in the school year (ie, those born between January and April), the cumulative incidence of an ADHD diagnosis was greatest for the youngest children (ie, those born between September and December); for boys the incidence ratio was 1·26 (95% CI 1·18–1·35; p<0·0001) and for girls it was 1·31 (1·12–1·54; p=0·0007). The asso...
Source: The Lancet Psychiatry - Category: Psychiatry Source Type: research