The Efficacy and Effectiveness of Online CBT - Jeroen Ruwaard

2.4. Discussion 29The effects on anxiety appeared to be small. However, after three-years the (uncontrolled)effects were large on all outcome measures. Participants were highly satisfiedwith their treatment and their therapists.2.4.1 Evaluation of effect sizeThe substantial improvement of the participants in the waiting list control group considerablydeflated the effects between treatment and control group. The improvementobserved in the waiting-list control group is comparable to that observed in otherstudies (Lange, van de Ven, & Schrieken, 2003; Zetterqvist et al., 2003). Zetterqvistet al. (2003) provided several explanations for these improvements, including thebeneficial effects of pretesting and the prospect of treatment. In the current study,the recruiting article and the website provided psycho-education that may have hadbeneficial effects. Possibly, the participants in the control condition benefited from theinformation they received, combined with the knowledge that they would start theactive treatment in the near future. However, these explanations remain speculative.The use of different types of control groups may shed light on the source of the effectsin the control group.Notwithstanding the improvement in the control group, the observed betweengroup effects are similar to those reported in the literature. The (controlled) effects onstress (d = .6) and depression (d = .4) compare well with the effects of face-to-faceCBT (d = .7 and d = .3 respectively; van der Klink et al., 2001). In addition, theresults corroborate results obtained by Zetterqvist et al. (2003) in an RCT of anInternet-driven stress-reduction program. In that study, the effect sizes were high,but intention-to-treat analyses failed to reveal statistically significant between effects.In contrast, all between effects in the present study were significant on an intentionto-treatbasis. This was perhaps due to the larger sample size and the use of a morepowerful statistical technique.2.4.2 MaintenanceThe uncontrolled three-year follow-up showed a high impact of the treatment withlarge effect sizes after three years, on stress and depression, and on emotional exhaustionand anxiety. This is consistent with our findings in the study on posttraumatic