What is intellectual disability and how common is it?
Epidemiological research shows a prevalence of intellectual disability of about 0.7% (a figure mostly derived from service registrations—funding bodies or service providers).7 8 In a recent conceptual review, Mont challenges the usefulness of a single summary indicator to capture disability,9 which is not a health condition borne by an individual. Rather, disability is, he says, “complex and multifaceted, with its roots in culture” (p 1662).9 Traditional society guidelines define intellectual disabilities as conditions characterised by substantial limitations both in intellectual functioning and in adaptive behaviour as expressed in conceptual, social, and practical adaptive skills, originating before age 18.10 More specific classification or aetiological diagnoses are based on known reasons for the disability, applying criteria such as those contained in the text revision of the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM IV-TR) or the American Psy
