Previous research has suggested substantial variation in prevalence rates of psychiatric disorders in individuals with intellectual disability and also differential patterns of associations between psychiatric disorders and challenging behaviours in people with intellectual disabilities. The aim of this study was to determine with the prevalence rate of specific psychiatric disorders and challenging behaviours and the relationship between them in a community based sample of individuals with intellectual disability.

A community based sample of 159 adults primarily with mild and moderate intellectual disabilities was surveyed for the presence of psychiatric disorders and challenging behaviour using the Behaviour Problem Inventory (BPI) and the Psychiatric Assessment Schedule (PAS-ADD). Individuals who met threshold on the PAS-ADD were subsequently evaluated using the Mini- PAS-ADD Interview.

Screening for psychiatric disorder using the PAS-ADD indicated a prevalence rate of 10%. There was a large discrepancy between the overall rate of challenging behaviour (45%) and the rate of psychiatric disorders identified by the Mini PAS-ADD Interview (6%). However, the rate of more severe behaviour problems (8%) was closer to the rate of psychiatric disorders (6%). Thirty one percent of people with severe challenging behaviours also were rated as having psychiatric disorders and odd ratio analysis indicates that individuals with severe challenging behaviour are substantially more likely to present with a psychiatric disorder. However, there does not appear to be a relationship between different topographies of challenging behaviour and discrete diagnostic categories of psychiatric disorder.