Previous studies have shown the effectiveness of guided Internet-based interventions for depression compared to control groups. It is often hypothesized that Internet-based treatments are associated with lower costs, because face-to-face time with therapist is reduced. The objective of this study was to conduct an individual-participant data meta-analysis (IPD-MA) evaluating the cost-effectiveness of guided Internet-based interventions for depression compared to controls from a societal perspective.

A systematic literature search was conducted in electronic databases from 2000 to January 1^{st RESULTS:}

IPD from five studies, including 1,426 participants were used. The guided Internet-based interventions were more costly than the controls, but not statistically significantly so (e.g.12-months mean difference = €406, 95%CI: -611 to 1,444). Cost-effectiveness acceptability curves indicated that high investments are needed to reach an acceptable probability that the intervention is cost-effective compared to control for CES-D and response to treatment (e.g., at 12-month follow-up the probability of being cost-effective was 0.95 at a ceiling ratio of 2,000 €/point of improvement in CES-D score). For QALYs, the intervention's probability of being cost-effective compared to control was low at the commonly accepted willingness-to-pay threshold (e.g., at 12-month follow-up the probability was 0.29 and 0.31 at a ceiling ratio of 24,000 and 35,000 €/QALY, respectively).

Guided Internet-based interventions for depression were not considered cost-effective compared to control. However, only a minority of RCTs investigating the clinical effectiveness of guided Internet-based interventions also assessed cost-effectiveness. Therefore, it is important that future RCTs measure resource use and productivity losses alongside clinical effectiveness.