Abstract
BACKGROUND: Studies on positive psychology interventions (PPIs) have frequently demonstrated benefits for healthy participants and patients. However, effect sizes are moderate, and underlying inter-individual differences in responses were rarely investigated. AIMS: We investigated whether severity of depression and subjective evaluation of PPIs are relevant sources of variance in this respect. METHOD: A 4-week group PPI programme (one 45-min session per week) was offered to 38 in-patients with depression. The control group (n = 38) was carefully matched and received treatment as usual. In the PPI group, emotional states were recorded before and after each session (responsiveness). Beck Depression Inventory-II scores at hospital admission and discharge were used to evaluate clinical effectiveness. The number of comorbidities (as an indicator of severity of disease) and patients' evaluations of the PPI sessions were used as additional independent factors for overall treatment outcome. RESULTS: The PPI induced a highly significant improvement in positive emotional state and decrease in negative emotional state, indicating responsiveness. Moreover, positive affectivity increased from week to week only in patients with a low number of comorbidities (indicating effectiveness). With respect to overall treatment outcome (Beck Depression Inventory-II scores), positive attitude toward the PPI resulted in the largest improvement. CONCLUSIONS: The results partly explain the variance in the effectiveness of PPIs. Moreover, they support the idea of personalised psychotherapy, and may inform discussion on whether patients with depression should be included in PPIs. However, additional individual characteristics should increase knowledge about individual predictors for effectiveness.