Processes of change in digital interventions for depression: A meta-analytic review of cognitive and behavioral mediators

The efficacy of digital interventions for depression has been established. In contrast, only limited knowledge on their change processes is currently available, and precise effect size estimates for mediators are pending. This study aimed to systematically review mediation studies and meta-analytically evaluate indirect effects of cognitive and behavioral mediators in digital interventions for adults with depression. The databases CENTRAL, Embase, MEDLINE, and PsycINFO were systematically searched for eligible randomized controlled trials. Two independent reviewers extracted the data, assigned mediators to eight categories and evaluated the methodological quality of included studies. Two-stage structural equation modeling was applied to synthesize indirect effects for cognitive and behavioral mediators. Overall, 25 studies (8110 participants) were eligible, which investigated 31 cognitive, 29 behavioral and 24 other mediators. Meta-analyses yielded significant indirect effects for combined cognitive mediators (ab = −0.068; 95 %-CI: [-0.093, −0.047]; k = 14 studies) and combined behavioral mediators (ab = −0.037; 95 %-CI: [-0.048, −0.028]; k = 13), but not for the specific cognitive mediators interpretation bias and dysfunctional attitudes. The systematic review revealed that all studies fulfilled at least five out of nine methodological quality criteria for psychotherapy process research, but the risk of bias assessment raised some concerns, particularly in regard to potential deviations from intended interventions. Overall, the findings of this meta-analytic review contribute to the understanding of the mechanisms of change in digital interventions for depression, and can inform the evidence-based advancement of future interventions.