Rasch analysis reveals comparative analyses of activities of daily living/instrumental activities of daily living summary scores from different residential settings is inappropriate

Objectives To internally validate a 15-item dichotomous activities of daily living (ADL) and instrumental activities of daily living (IADL) index. Study Design and Setting Data were extracted from The Older Persons and Informal Caregivers Survey Minimum DataSet (TOPICS-MDS). Using Rasch modeling, six aspects of the ADL/IADL scale were assessed: (1) overall fit, (2) internal consistency, (3) individual item and person fit, (4) local dependency, (5) targeting, and (6) differential item functioning (DIF) (RUMM 2030). All analyses were stratified by living situation [community-dwelling (n = 21,926) or residential care facility (n = 2,458)]. Results In both settings, "eating" was the easiest activity on the scale and "performing household tasks" was the most difficult activity. However, based on the location on the logit scale, the level of difficulty for certain items varied between residential settings, suggesting summary scores are not equivalent between these settings. DIF by gender and age group was observed for several items, indicating potential measurement bias in the scale. Conclusion Unless adjustments are undertaken, ADL/IADL summary scores retrieved from older persons residing in the community or residential care facilities should not be directly compared. This 15-item scale is poorly targeted for a community-dwelling older population, underscoring the need for items with improved discriminative ability.