Fig. 1: The statistical analysis strategy.

First, we conducted three independent factor analyses to group clinical variables. Next, we calculated a regression to determine the effects of age and sex on the SASP index. We then utilized correlation and regression analyses to explore the association between the SASP index and the factors. Finally, we split the sample into participants with early-onset depression (age of onset before 65 years) or late-onset depression (age of onset at or after 65 years) and repeated the regression analyses for these two subgroups. References: MADRS³⁶, ASI³⁷, SSI³⁸, Medical Outcomes Survey—mental³⁹, MMSE⁴⁰, RBANS⁴¹, DKEFS⁴², BMI, Medical Outcomes Survey—physical³⁹ and SASP.