A validated interview schedule for use in population surveys of chronic disease and disability.

The popular concept of a disabled person is of someone who has lost a limb or who is physically deformed in some obvious way. This concept is largely based on the appreciation of structural damage; severity is considered to be dependent on the extent of the damage and criteria based on this approach govern the assessment and award of the disability pensions at present available. However, disability may be thought of in terms of behaviour and performance and may be considered as limitation of the performance of an individual when compared with a 'fit' person. This concept considers disability as a disorder of function rather than a structural abnormality or loss. In America, reports of the Committee on the Medical Rating of Physical Impairment (1958) distinguish between these two approaches. The concept of the total functional loss is considered to be disability whereas the anatomical or structural abnormality is described as impairment. We have adopted this distinction but define these two terms more strictly. We define disability as limitation of performance in one or more activities which are generally accepted as essential basic components of daily living, such that inability to perform them necessitates dependence on another person. The severity of disability is thus proportional to the degree of dependence. The areas of activity essential are (I) mobility: walking, negotiating stairs, transfer in and out of bed or chair, and travel; (2) self-care: feeding, dressing, and toilet care; (3) domestic duties: shopping, preparation and cooking of food, household cleaning, and washing of clothes; and/or (4) occupation: the ability to hold unmodified employment in open industry consistent with the individual's age, sex, and skill. We define impairment as an anatomical, pathological or psychological disorder which may be described in diagnostic or symptomatic terms. It may