The hierarchical relationship between activities of daily living and instrumental activities of daily living.

A three-level hierarchical scale including IADL (shopping and transportation) and ADL (bathing, dressing, transferring, and feeding) was tested and validated based on secondary analysis of three studies of elders in the community: a population-based sample, the Cleveland-GAO, and two service-based samples, the Alternative Health Services Project, a study of Medicaid-eligible elders in Georgia, and the Section 222 Homemaker-Day Care study, a sample of Medicare-eligible elders. Scalability analysis included evaluation of Kronbach's alpha, Guttman analysis, and analysis of the pairwise association of individual items using phi/phi max. Validation included discriminant validity and predictive validity. With respect to discriminant validity, the negative association between functional ability (as measured by the scale) and age was observed. With respect to predictive validity, the negative relationship between functional ability (as measured by the scale) and risk of decline to ADL, death, and hospitalization in a year was observed. A six-level scale similar in structure and detail to the Katz Index of ADL was examined with the three studies. This scale can be used to described a broader range of needs of elders in the community and will be particularly useful to health services planners, practitioners, and researchers.