Effectiveness of a web-based cognitive behavioural intervention for subthreshold depression: Pragmatic randomised controlled trial

Background: Research on the effectiveness of treatments for subthreshold depression (sD) is still scarce. The aim of the study was to evaluate the efficacy of a web-based guided self-help intervention (GET.ON Mood Enhancer) in the treatment of sD. Methods: Participants with sD (n = 406) recruited from the general population via a large health insurance company were randomly allocated to a web-based cognitive behavioural intervention or to enhanced care-as-usual. The primary outcome was the reduction in depressive symptom severity as measured with the Center for Epidemiological Studies Depression Scale at post-treatment and at 6-month follow-up. Results: Participants in the intervention group showed a significantly greater pre-post reduction in depressive symptom severity (d = 1.06; 95% CI: 0.86-1.27) compared to the control condition (d = 0.29; 95% CI: 0.10-0.49). The corresponding between-group effect size was d = 0.69 (95% CI: 0.49-0.89). At 6-month follow-up the effect was reduced to d = 0.28 (95% CI: 0.09-0.48) but was still statistically significant (F