Population prevalence of psychopathology in children and adolescents with intellectual disability: II. Epidemiological findings.

This paper reports findings from an epidemiologically derived population in a multicentre study in NSW, Australia. The design of this study is described in the accompanying paper. Those with mild intellectual disability (ID) were likely to have been underascertained, but identification and participation rates for those with more severe ID were high. The study found that in the regions surveyed 40.7% of those with ID and aged between 4 and 18 could be classified as having severe emotional and behaviour disorder or as being psychiatrically disordered. The profoundly intellectually handicapped had lower levels of disturbance overall compared with those with mild, moderate and severe ID. The level of ID affected scores on a number of behavioural dimensions, with disruptive and antisocial behaviours more prominent in the mild ID group, and 'self-absorbed' and 'autistic' behaviours more prominent in those with severe ID. Age and sex did not affect prevalence, a finding that is in contrast to that found in general child psychopathology. The study found that fewer than 10% of children with intellectual disability and major psychiatric disorder had received specialist assistance.