Modifiable Psychological Variables as Predictors of Return to Work: Temporal Patterns in a Longitudinal Observational Study

Background: Common mental disorders (CMDs), including depression, anxiety, and adjustment disorders, are leading causes of long-term sickness absence (SA) and work disability in high-income countries. Despite the significant burden, evidence-based interventions to support return to work (RTW) remain limited. This study aimed to investigate the predictive role of selected modifiable psychological factors on RTW among individuals on sick leave for CMDs, with particular emphasis on temporal dynamics during the early phase of the RTW process. Methods: A longitudinal observational study was conducted with bi-weekly self-reported questionnaire measurements for 3 months and quarterly follow-ups for 12 months. Outcomes were self-reported RTW and registry-based net SA days (NSAD). Analyses included robust linear mixed models for focal predictor trajectories, Bayesian logistic regression with a regularizing horseshoe prior for the probability of RTW, and ordered beta regression for NSAD since sick-days data have lower and upper bounds. Results: Baseline measurements of RTW-SE and Work Ability Scores (WAS) were also associated with RTW at three months. Improvement in RTW self-efficacy (RTW-SE) during the first three months showed the strongest and most consistent association with increased probability of RTW, both cross-sectionally at 3, 6, and 12 months, and longitudinally. Improvement regarding physical fatigue and WAS were associated with approximately 18% less NSAD at 3 and 6 months, while cognitive exhaustion showed similar impact but only at three months.