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BACKGROUND: Disability in instrumental activities of daily living (IADLs) or activities of daily living (ADLs) is an indicator of health risk. The inclusion of these items in population screens may be limited by variation in item performance across gender and age groups. Further, identification of shortened lists may encourage inclusion of these items in screens. METHODS: We applied item response theory (IRT) methods to assess the responses of 9865 community-dwelling elders in the 1993 Medicare Current Beneficiary Survey to 11 IADL/ADL items. Items were classified as "receive help/not receive help" for the overall population and stratified by age and gender. We assessed the same IADL/ADL items using responses classified as "difficulty/no difficulty." After eliminating items that performed poorly, we performed all-subsets analyses to identify abbreviated sets of items that would select the highest proportion of persons with IADL/ADL disability. RESULTS: Responses classified in receive help format showed consistency by gender and age group. Changing the response classification to difficulty/no difficulty influenced the reported order and relationship of IADL/ADL items. Receipt of help for any one of five items--shopping, doing light housework, walking, bathing, or managing finances--identified 93% of individuals receiving help with any IADL/ADL. A slightly different set of five items--walking, shopping, transferring, doing light housework, or bathing--identified 91% of persons reporting difficulty with any IADL or ADL. CONCLUSIONS: The relationship of IADL and ADL items to the underlying construct of disability was similar for men and women. The relationship was also similar for oldest-old and younger-old individuals. This study also identified abbreviated lists of disability items that can be used to efficiently screen community-dwelling elders for the presence of IADL/ADL disability.
Saliba et al. (2000) studied this question.