Objective: This study addresses the question of how prevalence and patterns of psychiatric disorder change from childhood to adolescence in young people with intellectual disability (ID).
Method: A representative epidemiological sample of 582 young people with ID aged 4-19 years was surveyed in 1991-1992 and again in 1995-1996. The main measure of psychiatric disturbance was the developmental behaviour checklist (DBC), a 96 item parent/carer completed questionnaire with robust psychometric properties which provided an overall score, 6 subscale or syndrome measures of psychiatric disturbance and determined caseness.
Results: The findings confirmed that about 40% of young people with ID had psychiatric disorders which persisted over 4 years. Clinically significant change in symptoms with either deterioration or improvement occurred in around 14% of the sample.
Conclusion: Psychiatric disorder is 3-4 times more prevalent in young people with ID than in the general population. Less than 10% of these young people receive specialist services for a problem which is numerically as large as schizophrenia.