Legal definitions of intellectual disability: do they work?

Aim: To consider how well the current legally recognized definitions of intellectual disability in the UK and US fulfil their role, in the light of the recent work that has shown that our ability to measure low IQ is severely limited (Whitaker 2010, 2013). Method: Based on a literature search current UK and US definitions of intellectual disability (including mental retardation) were found and examined to see to what extent they incorporated a specified IQ score. Results: A substantial number of the US definitions, notably the AAIDD, DMS-V and many of the definitions of individual states, require a measured IQ below a specified figure. In the UK the definition used in the Department of Health (2001) also implies that there should be an IQ less than 70. Conclusions: Many of the current legally recognised definitions are not fit for the purpose for which they were intended. It is suggested that the definitions be re drafted so that they take account of our lack of ability to measure low IQ and better reflect the needs of the stakeholders in the situations where that definition is required.