surveys related to disability? If so, what are the ramifications on nonresponse bias? If proxy responses are accepted, what impact does this design choice have on the measurement error properties of the reporting of disability?

As is evident from the alternative design components discussed above, each choice impacts the error structure of the estimates of disability and the analytic capabilities that can be addressed with the resulting data. SSA will need to decide how much error both ways it will be willing to tolerate, taking into consideration costs, information needs, and other factors. Also evident is the lack of information with respect to the specific impacts of design choices on the reporting of impairments and disabilities.

One could consider a number of various permutations of design choices outlined above in designing a work disability monitoring system. These options could be arrayed along lines of richness of the data, quality of the data, and costs. At one end of the spectrum is a monitoring system characterized as a continuous, longitudinal, multimode household-based data collection, which may be supplemented periodically with medical examinations (for those meeting a particular threshold based on the household data and a subset of those who are classified in the category adjacent to the threshold) and links to administrative records. Such a design would facilitate analysis of change over time in the size of the pool of eligible population and applicants, as well as understanding of the individual and environmental factors that influence application for benefits, and would simulate the impact of alternative decision processes, provided that the household survey, medical examination, and administrative records collected or contained the information necessary for such modeling. This comprehensive design would be the most costly.

At the other end of the spectrum are data characterized by a small number of questions on disability included as part of repeated cross-sectional surveys. Such a design would allow analysts to monitor the size of the pool of eligible population, and possibly, if crosswalk analytic capabilities had been developed, the size of the pool of applicants. However, it does not facilitate understanding of how individual, environmental, and macro level changes impact the application process. This minimal design would be least costly.

Design Options for Continuous Monitoring

Continuous monitoring should be undertaken using one or more design options; each of which requires some statistical coordination. These may include



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