Differential item functioning analysis of items on the Geriatric Depression Scale-15 based on the presence or absence of cognitive impairment.

Objective: The Geriatric Depression Scale-15 (GDS-15) is a screener for depressive symptoms in older adults. The present study aims to investigate the differential item functioning (DIF) of the GDS-15 items to determine whether or not they are biased by the presence of cognitive impairment.

Method: Data from 215 older patients were used to examine the GDS-15. Individuals were categorized as cognitively impaired if they scored below the 10th percentile on the Mattis Dementia Rating Scale II. To evaluate DIF, configural invariance, metric invariance, scalar invariance, residual invariance, and factor variance were evaluated. Additional analyses were conducted to know the role identified DIF items play in the screening process.

Results: Most levels of invariance indicated that items operated equivalently across groups (p > 0.05). However, analysis of scalar invariance indicated worse model fit (p = 0.001), such that the threshold for Item 13 differed between the groups. Freeing this threshold resulted in scalar invariance (p = 0.12).

Conclusions: Because partial measurement invariance was achieved suggesting that the tool as a whole functions similarly for older adults with and without cognitive impairment, professionals can be confident that the GDS-15 screens for depression as well in individuals with cognitive impairment as those without.