Is the 15-item Geriatric Depression Scale a Fair Screening Tool? A Differential Item Functioning Analysis Across Gender and Age.

The 15-item version of the Geriatric Depression Scale (GDS-15) is widely employed to assess depression in old people, but it is unclear if there are biases in the total score depending on respondents' gender and age. In the current study, we investigated the measurement equivalence of the GDS-15 to provide evidence that the test is a fair screening tool when administered to young-old, old-old, and oldest-old men and women. Item Response Theory-based Differential Item Functioning analyses were applied on a large sample of Italian old people. One item exhibited Differential Item Functioning when comparing men and women, and one item showed Differential Item Functioning across different age-groups. Nonetheless, the magnitude of Differential Item Functioning was small and did not produce any differential test functioning. The gender and age measurement equivalence of the GDS-15 confirms that the test can be used for clinical and research screening purposes.