Sample size, sample size planning, and the impact of study context: systematic review and recommendations by the example of psychological depression treatment

Free choice of treatment content, support on demand and supervision in internet-delivered CBT for adults with depression: A randomized factorial design trial

Even if much is known regarding the effects of internet-delivered cognitive behaviour therapy (ICBT) for depression there are several topics that have not been studied. In this factorial design trial with 197 participants we investigated if clients in ICBT could select treatment modules themselves based on a selection of 15 tailored treatment modules developed for use in ICBT for depression. We contrasted this against clinician-tailored module selection. We also investigated if support on demand (initiated by the client) could work as well as scheduled support. Finally, we tested if clients that were mentioned in supervision would improve more than clients not mentioned (with the exception of acute cases). The treatment period lasted for 10 weeks, and we measured effects at post-treatment and two-year follow-up. Measures of depression and secondary outcomes were collected at pre-treatment, post-treatment and two-year follow-up. Overall, within-group effects were large across conditions (e.g., d = 1.73 on the BDI-II). We also found a small but significant difference in favour of self-tailored treatment over clinician-tailored (d = 0.26). Within-group effects for the secondary measures were all moderate to large including a test of knowledge about CBT. The other two contrasts "support on demand" and "supervision" yielded mostly non-significant differences, with the exception of a larger dropout rate in the support on demand condition. There were few negative effects (2.2%). Effects were largely maintained at a two-year follow-up. We conclude that clients can choose treatment modules and that support on demand may work. The role of supervision is not yet clear as advice can be transferred across clients.