Definition and prevalence of learning disability

Learning disability is the term adopted by the Department of Health to describe what has previously been termed mental handicap, and while controversy remains as to the most appropriate terminology (Gath, 1992), we will use learning disability in this chapter. The essential elements of learning disability include intellectual and other associated impairments arising during the developmental period, most frequently around the time of birth, and resulting in long-term disability in performing some or all of the major life activities which require intellectual and social function. Learning disability is often divided into moderate, and severe or profound. Such broad terms tend to obscure the individual's mix of abilities and disabilities, often concentrating on the deficits in a negative way. However, it is important to recognise that the label covers a very wide range of abilities, and this in turn will affect both the manifestation and management of mental illness in people with learning disability.

Estimating the prevalence of learning disability is difficult. A variety of different methods of identification have been used, as well as differing definitions, so that figures will vary with the age profile, and location of a particular population. The estimated lifetime prevalence of mild learning disability is about 3% in the United Kingdom, and the more disabled group, including moderate to profound learning disability, is ten times less common, occurring in about 3 per 1000 at school age (Fryers, 1984).