Using national surveys for mental health surveillance of individuals with intellectual disabilities in Canada.

INTRODUCTION Individuals with intellectual disabilities have a higher prevalence of health problems, including psychiatric and behavioural conditions, than the general population. However, there is little population-based information in Canada about individuals with a dual diagnosis of psychiatric disorder and intellectual impairment. The aim of this study was to determine whether the 2005 Canadian Community Health Survey (CCHS) and the 2006 Participation and Activity Limitation Survey (PALS) could be used to estimate the prevalence of dual diagnosis in Canada. METHODS We undertook a secondary analysis of two population-based surveys to determine if these could be used to estimate the prevalence of psychiatric or behavioural conditions among adults with intellectual disabilities in Canada. RESULTS The surveys reflect prevalence estimates of intellectual disabilities (CCHS: 0.2% and PALS: 0.5%) that are considerably lower than those published in the literature. While it was possible to calculate the proportion of individuals with a dual diagnosis (CCHS: 30.6% and PALS: 44.3%), the surveys were of limited use for detailed analyses. The estimates of prevalence derived from the surveys, especially from the CCHS, were of unacceptable quality due to high sampling variability and selection bias. CONCLUSION The estimates should be interpreted with caution due to concerns regarding the representativeness of the sample with intellectual disabilities in the national surveys.