Population prevalence of psychopathology in children and adolescents with intellectual disability: I. Rationale and methods.

Our knowledge of the epidemiology of psychopathology in children and adolescents with intellectual disability (ID) is hampered by a number of factors. These include the relative scarcity of studies of children rather than adults, the study of non-epidemiological samples such as those in institutions or those attending psychiatric clinics, a lack of standardized methods of assessment of psychopathology, studies with numbers too small to provide adequate confidence intervals around identified prevalence rates, insufficient detail concerning symptoms or syndromes as well as disorder, and a lack of consistent data concerning the effects of basic demographic variables such as age, sex and IQ. Despite these limitations, it is clear that psychopathology is several times more prevalent in children and adolescents with ID than in those without this disability. This paper reviews findings from previous studies and describes the methodology of a new study using the Developmental Behaviour Checklist.