Intellectual disability as a disorder of reasoning and judgement: the gradual move away from intelligence quotient-ceilings

Abstract

Purpose of review: Adoption of the term intellectual disability (intellectual developmental disorder, IDD) in DSM-5 represents a shift from a disability (test score) emphasis to a disorder (medical/neurobiological) emphasis. Several implications of this shift for definition and diagnosis of intellectual disability (ID) are discussed.

Recent findings: The intellectual disability (IDD) section of DSM-5 reflects a growing concern about excessive and inappropriate reliance on intelligence quotient (IQ) cut-offs. Clinicians are now encouraged to take into account various sources of test error; rely more on neuropsychological profiles of cognitive impairments; and approach the adaptive functioning of patients with a greater emphasis on cognitive aspects, such as risk-unawareness.

Summary: A psychometric approach to intellectual disability/IDD, defining it solely in terms of test scores, is inappropriate for psychiatric and medical disorders, which use a disorder rather than a disability model. The intellectual disability/IDD section in DSM-5 is the first prototypical attempt to broaden the category, and approach it in more clinical terms, while still maintaining the meaning of the condition.