What matters in the end? : An experimental factorial follow up study investigating the importance of the effect of different treatment components in internet delivered cognitive behavioral therapy among adults suffering from depressive symptoms

Depression is one of the most common psychiatric health problems worldwide which causes great suffering among the affected individuals and causes heavy national economic losses. Few studies have examined the treatment effects of various treatment components in Internet cognitive behavioral therapy (ICBT) as well as the long term effects for depression. The treatment method as such has indicated large effects both immediately after treatment and in limited follow ups, up to one year. In the present study long time effects in ICBT and the various 4 treatment components support type, who is in charge of the content in treatment and supervision has been examined with a mixed factorial design within a group of adults suffering from depression (N=197). Further, the impact of acquired knowledge about treatment content on symptom reduction examined two years post treatment. Previous research has indicated divergent results in the interaction between acquired knowledge and treatment outcome. The results indicated moderate to large effects of treatment two years post treatment independent of treatment component (d =.51- 1.63). Persistent treatment effects were found in the majority of the outcome measures, measured immediately after treatment to the follow up two years post treatment. One advantage was found for the participants who received therapist with supervision on the outcome of sleeping difficulties in comparison with those who received a therapist without supervision (ղᵖ²=.076). One further advantage was found for acquired knowledge among participants who was assigned content in treatment chosen by the therapist and at the same time received support on demand in comparison with participants who got to choose treatment content by themselves and was received scheduled support. Also participants who got to choose treatment content by themselves and received scheduled support had an advantage in comparison with those who got to choose treatment content by themselves and received support on demand (ղᵖ²=.045; ղ ᵖ²=.039). Acquired knowledge did not indicate any correlations with depressive symptoms. The findings of the study indicate that ICBT is an effective treatment method among adults suffering from depression even in long term follow ups, and that the importance of specific treatment components need further research