Objective: The purpose of this analysis was to examine the stability over time of the activities of daily living (ADL) and instrumental activities of daily living (IADL) items in the Aging in Manitoba (AIM) Longitudinal Study and to evaluate the existence of differential item functioning across settings (home, nursing home).
Study design and setting: The study used data from 607 participants of the AIM Longitudinal Study who were more than 85 years of age in 1996 and who had complete data from 1983, 1990, and 1996 for all ADL and IADL items. Rasch analysis was used to examine how the rating scale of the ADL and IADL items was used by participants, and to determine if the ordering of items remained stable across three time periods (1983, 1990, 1996) and the two different settings (home, nursing home).
Results: The rating scale worked best when dichotomized into "received no assistance" and "receives assistance." Except for four items (making tea, making meals, doing nursing care, and going outside in any weather), the items were stable across administration periods, and across settings.
Conclusion: The AIM can be used to evaluate changes in disability over time and may have the potential to identify those at risk for transitions in care.