New avenue for the geriatric depression scale: Rasch transformation enhances reliability of assessment.

•This article is the first to show conversion tables to transform the raw 15-item geriatric depression scale (GDS-15) scores into interval-level data.•Person separation index (PSI) was improved by combining locally dependent items into six super-items (PSI = =0.77).•The best Rasch model fit (χ2(28)=37.72, p = =0.104).•Reliability and psychometric characteristics of the GDS-15 were improved and now satisfy expectations of the unidimensional Rasch model.