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This study examined patterns of comorbid/associated diagnoses and associated problems in a population sample of children with and without DSM-III-R attention-deficit hyperactivity disorder (ADHD). Half (N = 409) of a mainstream school population of Swedish 7-year-olds were clinically examined, and parents and teachers were interviewed and completed questionnaires. The children were followed up 2-4 years later. Eighty-seven per cent of children meeting full criteria for ADHD (N = 15) had one or more and 67% at least two--comorbid diagnoses. The most common comorbidities were oppositional defiant disorder and developmental coordination disorder. Children with subthreshold ADHD (N = 42) also had very high rates of comorbid diagnoses (71% and 36%), whereas those without ADHD (N = 352) had much lower rates (17% and 3%). The rate of associated school adjustment, learning, and behaviour problems at follow-up was very high in the ADHD groups. We concluded that pure ADHD is rare even in a general population sample. Thus, studies reporting on ADHD cases without comorbidity probably refer to highly atypical samples. By and large, such studies cannot inform rational clinical decisions.
Kadesjö et al. (Tue,) studied this question.