Impairment, disorder and disability are familiar terms introduced by the World Health Organization (WHO) in 1980. In the WHO classifications, impairment is defined as an abnormality of a structure or function; disability is the functional consequence of impairment; and handicap is the social consequence of impairment.

The Department of Rehabilitation Services embraces a slightly different model from the NIH National Center for Medical Rehabilitation Research, which describes five levels of function.

  • Pathophysiology – Interruption or interference with normal physiologic and developmental processes or structures.
  • Impairment – Loss or abnormality of cognitive, emotional, physiologic or anatomical structure or function, including all losses or abnormalities, not only those attributable to the initial pathophysiology.
  • Functional Limitation – Restriction or lack of ability to perform an action in the manner within the range consistent with the purpose of an organ or organ system.
  • Disability – Inability or limitation in performing tasks, activities and roles to levels expected within physical and social contexts.
  • Societal Limitation – Restriction attributable to social policy or barriers (structural or attitudinal) that limits fulfillment of roles or denies access to services and opportunities that are associated with full participation in society.