Although the 15-item Geriatric Depression Scale (GDS15) is a widely used depression screening questionnaire, the implications of the GDS15 in patients with Alzheimer's disease (AD) are questionable. We designed this study to explore the GDS15 factor structure and the relationships between these factors and cognitive-behavioral aspects.

The GDS15, cognitive function tests, and the Korean-Neuropsychiatry Inventory were administered to 310 patients with probable AD, who were not medicated before visiting the hospital. Three factors were identified by principal components analysis. A bivariate correlation analysis was conducted to determine the relationships between factors and neurocognitive and behavior symptoms.

Factor 2 was correlated with the Korean Boston Naming Test, calculating ability, the go-no-go test, the Controlled Oral Word Association Test (COWAT), the Color Word Stroop Test (CWST; words and color), aggression, depression, and apathy. Factor 3 was correlated with calculating ability, the Seoul Verbal Learning Test, immediate recall, copy, and delayed recall on the Rey-Osterieth Complex Figure Test, contrasting on the COWAT, and words and delusion on the CWST. We identified three factors and revealed that the GDS15 may be comprised of a heterogeneous scale.

These results suggest that the GDS15 may be comprised of a heterogeneous scale and suggest multi-dimensional properties of the GDS15 in patients with AD.