Differential item functioning due to cognitive status does not impact depressive symptom measures in four heterogeneous samples of older adults

Objective: The objective of this study is to determine whether differential item functioning (DIF) due to cognitive status impacted three depressive symptoms measures commonly used with older adults. Methods: Differential item functioning in depressive symptoms was assessed among participants (N=3558) taking part in four longitudinal studies of cognitive aging, using the Geriatric Depression Scale, the Montgomery-angstrom sberg Depression Rating Scale, and the Center for Epidemiologic Studies Depression Scale. Participants were grouped by cognitive status using a general cognitive performance score derived from each study's neuropsychological battery and linked to a national average using a population-based survey representative of the US population. The Clinical Dementia Rating score was used as an alternate grouping variable in three of the studies. Results: Although statistically significant DIF based on cognitive status was found for some depressive symptom items (e.g., items related to memory complaints, appetite loss, lack of energy, and mood), the effect of item bias on the total score for each scale was negligible. Conclusions: The depressive symptoms scales in these four studies measured depression in the same way, regardless of cognitive status. This may reduce concerns about using these depression measures in cognitive aging research, as relationships between depression and cognitive decline are unlikely to have been due to item bias, at least in the ways that were measured in the datasets we considered. Copyright (C) 2014 John Wiley & Sons, Ltd.