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Lawton and Brody's eight-item Instrumental Activities of Daily Living (IADL) scale is used often with elderly patients but scored in several different ways. We scored the IADL with seven popular procedures ranging from relatively simple to complex (Guttman scores, summed and Rasch scores from dichotomous, trichotomous, and polytomous items) in a sample of rural elders (N = 231). We compared the IADL scales' prediction of concurrent cognitive functioning, depressive symptoms, psychosocial functioning, and health care use (medications, outpatient visits, inpatient days). Validity coefficients ranged from small to large among outcome variables but were highly consistent across IADL scoring procedures. Consequently, researchers and clinicians may prefer to use simpler IADL scoring procedures with this population.
Vittengl et al. (Tue,) studied this question.