Doubtful prospective effect of optimism on depression: A simulated reanalysis and comment on Karhu et al. (2024)

Based on findings from analyses with cross-lagged panel models, Karhu et al. (2024) concluded that optimism may intervene against depression. Here, we simulated data to resemble the data used by Karhu et al. We used triangulation and fitted complementary models to the simulated data and found contradicting decreasing and increasing effects of initial optimism on subsequent change in depression. These divergent findings suggest that it is premature to assume an intervening effect of optimism on depression and the conclusion by Karhu et al. in this regard can be challenged. It is important for researchers to be aware that correlations, including adjusted cross-lagged effects, do not prove causality in order not to overinterpret findings, something that appears to have happened to Karhu et al. We recommend researchers to triangulate by fitting complementary models to their data in order to evaluate if observed effects may be due to true causal effect or if they appear to be spurious.