Does recruitment source moderate treatment effectiveness? A subgroup analysis from the EVIDENT study, a randomised controlled trial of an internet intervention for depressive symptoms

Objective: This study aims to examine whether the effects of internet interventions for depression generalise to participants recruited in clinical settings.

Design: This study uses subgroup analysis of the results of a randomised, controlled, single-blind trial.

Setting: The study takes place in five diagnostic centres in Germany.

Participants: A total of 1013 people with mild to moderate depressive symptoms were recruited from clinical sources as well as internet forums, statutory insurance companies and other sources.

Interventions: This study uses either care-as-usual alone (control) or a 12-week internet intervention (Deprexis) plus usual care (intervention).

Main outcome measures: The primary outcome measure was self-rated depression severity (Patient Health Questionnaire-9) at 3 months and 6 months. Further measures ranged from demographic and clinical parameters to a measure of attitudes towards internet interventions (Attitudes towards Psychological Online Interventions Questionnaire).

Results: The recruitment source was only associated with very few of the examined demographic and clinical characteristics. Compared with participants recruited from clinical sources, participants recruited through insurance companies were more likely to be employed. Clinically recruited participants were as severely affected as those from other recruitment sources but more sceptical of internet interventions. The effectiveness of the intervention was not differentially associated with recruitment source (treatment by recruitment source interaction=0.28, p=0.84).

Conclusion: Our results support the hypothesis that the intervention we studied is effective across different recruitment sources including clinical settings.

Trial registration number: ClinicalTrials.gov NCT01636752.