vate contracts offering different kinds of benefits or services or in a survey context to measure inability to undertake major activities of daily living. No single definition is feasible or desirable that will fit all purposes of assessment.

Consider the main purposes to which definitions of disability are applied. A major purpose of most relevance to this report is eligibility for cash benefit programs such as Social Security Disability Insurance (SSDI) and Supplemental Security Income (SSI). Under these programs, the definition is used as a screening device. People who meet the definition receive the benefit, while those who fail to meet the definition are denied access to the benefit. The immediate and obvious constraint is that the screening of candidates for access to the benefit involves costs in terms of time of both applicants and screeners. The nature and type of these constraints under which the administering agency chooses to operate will depend on the value of the benefit that is being offered and the number of applicants. For example, the situation is obviously quite different comparing the benefits offered to applicants for a handicapped parking program and for the Social Security disability programs. No doubt the handicapped parking space is valuable to the applicant, but its value surely pales in comparison to that of income maintenance that may last a lifetime.

The monetary value of the benefit is relevant, but the resources available to screen the applicants are also important. In the Social Security disability programs, the benefits are quite valuable, whereas the resources devoted to screening applicants are limited in relationship to the demand for benefits. As the statutory definition makes clear, a person is considered “work disabled” based on the existence of a medical impairment or injury that precludes substantial gainful activity (SGA). With millions of applicants each year, SSA has to resort to administrative shortcuts in making decisions. Consequently SSA uses Listings of Impairments (Listings) as a critical early decision step to award or deny benefits. These Listings consist of medical evidence of more than 100 conditions that are considered to be of such severity that the condition can be presumed to constitute work disability regardless of the individual’s age, education, previous occupation, or other relevant factors.

Similar problems can be seen in the administration of other benefit programs such as workers’ compensation. In that state program, various states use different methods to judge eligibility for benefits. One benefit found in most of the state jurisdictions is for a permanent partial disability. An example of this is the American Medical Association Guides to the Evaluation of Permanent Impairment (AMA, 1993), which is a standardized system for translating the extent of an injury of a body part into a percentage of disability of the whole person. This type of system has been used for the assessment of compensation payments, including

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