underlying the measurement of disability in other surveys. In addition, we review what is currently known with respect to the error properties of survey-based estimates of the population of persons with work disabilities.

CONCEPTUAL ISSUES TO CONSIDER IN THE MEASUREMENT OF PERSONS WITH WORK DISABILITIES

As noted above, one of the issues of concern in the measurement of persons with work disabilities involves differences in the conceptual models underlying the measurement. The Social Security Act defines disability as the “inability to engage in any substantial gainful activity by reason of a medically determinable physical or mental impairment which can be expected to result in death or can be expected to last for a continuous period of not less than 12 months” (Section 223(d)(1)). The SSA definition implies a direct relationship between an individual’s attributes—specifically related to pathology, impairment, and functional limitation—and work disability. In contrast, Nagi (1991, p. 317) and other contemporary theorists characterize disability as a “… relational concept; its indicators include individuals’ capacities and limitation, in relation to role and task expectation, and the environmental conditions within which they are to be performed.” As noted by Jette and Badley (2000, p. 17):

The fundamental conceptual issue of concern is that a health-related restriction in work participation may not be solely or even primarily related to the health condition itself or its severity. In other words, although the presence of a health condition is a prerequisite, “work disability” may be caused by factors external to the health condition’s impact on the structure and functioning of a person’s body or the person’s accomplishments of a range of activities.

Most measures of work disability currently in use in U.S. federal surveys assume (or imply) that work disability relates to an individual’s attributes with respect to functional limitations; almost all such questions leave it to the respondent to attribute his or her labor force participation to an underlying health condition. However, the movement in the measurement of persons with disabilities and persons with work disabilities is toward measures that incorporate an understanding and assessment of the external factors that influence participation by individuals in work. It is conceivable that as new measures for the assessment of persons with work disabilities are developed and adopted in ongoing federal data collection efforts—that is, measures that incorporate an assessment of the environment (including accommodations, adaptations, and barriers)—the



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