IntroductionInternet-based self-help interventions have shown to be effective in the treatment of depression. Several meta-analyses indicated that human contact has a crucial impact on adherence and outcome. While most research focused on the role of guidance during interventions, a review by Andersson and Johansson (2012) suggested that contact before the intervention too may play an important role.ObjectiveWe investigated the impact of the degree of contact in internet-based interventions (IBIs) for depression on outcome in adults suffering from elevated symptoms of depression.MethodsWe conducted a preregistered meta-analysis (www.osf.io/4mzyd) and included trials comparing IBIs for depression against control conditions (treatment as usual [TAU] or waiting list [WL]) in patients with symptoms of unipolar depression searching the databases PsycINFO and Cochrane's Central Register of Controlled Trials (CENTRAL) limited to entries from EMBASE and PubMed. Following Andersson and Johansson (2012), contact before an intervention was defined as having had a diagnostic interview before the IBI, and contact during intervention was defined as having received guidance during the IBI. IBIs were grouped as providing (0) no contact, (1) contact before the IBI, (2) contact during the IBI, or (3) contact both before and during the IBI. The primary outcome was standardized mean difference (SMD) of the IBI and control in depressive symptoms at treatment termination. Secondary outcomes were study dropout and adherence to the IBI.ResultsWe included 56 eligible trials that randomized 13,335 patients to 75 internet-based intervention conditions and control groups (TAU in 23 trials, WL in 33 trials). In total, 44 trials (78.57 %) were judged to show some concerns or a high risk of bias. Overall heterogeneity was high regarding the primary outcome (I2s < 66 %) and even higher for secondary outcomes (I2s < 91 %). Degree of contact was a robust predictor of outcome and adherence in all pre-registered and exploratory analyses. We found the effect of the IBI to increase with higher degree of contact. However, in pair-wise contrasts, only IBIs offering both contact before and during the intervention (SMD = 0.573, 95 % CI: 0.437, 0.709) significantly outperformed interventions offering no contact (SMD = 0.224, 95 % CI: 0.090, 0.340).ConclusionsThe results suggest that contact before and during an intervention increases the effects of IBIs. The combination of contact before and during the intervention seems to a pivotal role regarding adherence as well as treatment outcome for patients suffering from depression.