Prevalence of intellectual disabilities and epidemiology of mental ill-health in adults with intellectual disabilities 

♦ The prevalence of intellectual disabilities varies, depending upon definition, country, time, age range, and methods of population ascertainment. Reported rates vary substantially, and may be in the order of 9–14/1000 childhood populations, 3–8/1000 adult populations in developed countries, and higher in developing countries. ♦ Mental ill-health is more commonly experienced by adults with intellectual disabilities than the general population. Point prevalence is about 40 per cent, with problem behaviours being the most prevalent type. ♦ Dementia, problem behaviours, autism, bipolar disorder, and psychoses are more prevalent than for the general population. ♦ Incident mental ill-health is also greater than for the general population, at about 8 per cent per year. Common mental disorders and psychoses both have higher incidence than that for the general population. ♦ There is limited information on the protective and vulnerability factors for mental ill-health. ♦ Some factors related to prevalence and incidence of mental ill-health are similar to those found in the general population suggesting similar underlying causative mechanisms, but other factors differ, suggesting that inferences cannot necessarily be drawn from general population data and applied to the population with intellectual disabilities. ♦ Identifying high-risk groups within the population may allow for the provision of early interventions and supports, whilst some causative factors may be amenable to interventions to prevent or improve mental ill-health in this population. We need to gain a better understanding of these issues.