LAUSR

Objective Characterize three functional living scales under item response theory and examine these scales for evidence of differential item functioning (DIF) by participant and/or informant ethnicity and education. Method Baseline data from 3155 participants [Mage = 70.59(9.55); Medu = 13.3(4.26); 61.72%female] enrolled in the Texas Alzheimer’s Research and Care Consortium with data from the Clinical Dementia Rating Scale (CDR; functional items), Physical Self-Maintenance Scale (PSMS), and Instrumental Activities of Daily Living Scale (IADL) were used. The sample was predominately white (93.94%) and 35.97% identified as Hispanic. Graded response models fit all three tests best. DIF was examined by iteratively dropping item-by-item constraints and then testing model fit. Results The CDR demonstrated overall good item functioning with clear separation between all of the rating categories for each item, while the PSMS and IADL did not, suggesting the item ratings should be reconsidered. DIF was observed by ethnicity (Hispanic v. non-Hispanic) and education (separated into low, average, high) for every item on all three scales (all ps ≤ .01 after adjustment for multiple observations). Hispanic ethnicity and higher education subjects were more likely to be rated as more impaired. Conclusions Results suggest these three commonly used functional scales have DIF depending on the ethnicity and education of the patient. This finding has implications for understanding functional change in certain populations, particularly the potential for mischaracterization of impairment in minority samples. The finding that individuals with higher education tended to be rated as more functionally impaired warrants further investigation.