Identifying the disabled: concepts and methods in the measurement of disability. By Lawrence D. Haber, 1967.

ESTIMATES OF the number of disabled people in the United States vary substantially, according to the particular concept and method used. The terminology used to describe disability is frequently inconsistent, and considerable confusion exists about concepts, criteria, and operational definitions. Different terms are used to designate similar aspects of disability, and the same terms are sometimes used to designate different aspects and levels of limitation. The methods of measurement common to survey research differ substantially from the disability evaluation procedures used in judicial and administrative decisions in benefit, compensation, and rehabilitation programs. Administrative disability determinations tend to rely primarily on the medical evaluation of impairment-often as the sole criterion for the evaluation of disabi1ity.l Population estimates based on survey interviews rely primarily on the respondent’s evaluation of his limitations in activities such as work, housekeeping, or school. Literally interpreted, disability refers to “loss or reduction of ability.” Definitions in use in clinical studies, survey research, and administrative evaluations commonly accept the loss or reduction of capacity to engage in normative role activities as the central point of reference of disability, with an origin in impairments or functional limitations resulting from disease or injury. The specification of activity requirements and the criteria for determining ability loss are, however, related to the research or administrative objectives.