Differential item functioning of the Geriatric Depression Scale-short form in the NACC dataset.

INTRODUCTION

This study examined differential item functioning of the Geriatric Depression Scale - Short Form (GDS-SF) in the National Alzheimer's Coordinating Center (NACC) Uniform Data Set (UDS) to identify potential variables that produce measurement bias.

METHODS

Data from 14077 individuals' first NACC visit were analyzed. Multiple indicator, multiple causes (MIMIC) models assessed differential item functioning (DIF) of the 15-item GDS-SF across race, Hispanic ethnicity, primary language, sex, and cognitive status (Clinical Dementia Rating [CDR] scale scores), while adjusting for educational attainment.

RESULTS

Participants were on average 73 (SD = 9.1) years old and 54.4% women. The majority (13 of 15) of the GDS-SF items demonstrated DIF. For many items, participants with any level of CDR cognitive impairment were more likely to endorse depressive symptoms.

DISCUSSION: Findings indicate the presence of widespread DIF by cognitive impairment severity such that individuals with even mild cognitive impairment may respond differently to certain items on this measure.

HIGHLIGHTS: The Geriatric Depression Scale - Short Form (GDS-SF) showed differential item functioning (DIF) in 13 of 15 items across demographic and cognitive groups. Only two items-hopelessness and worthlessness-were invariant across all groups. Cognitive status (Clinical Dementia Rating [CDR]) most strongly influenced item endorsement patterns. Our study used a large, diverse sample (National Alzheimer's Coordinating Center Uniform Data Set [NACC UDS]) and robust DIF analytic methods. Findings highlight both reliable and problematic GDS-SF items for older adults.