Components of therapy as mechanisms of change in cognitive therapy for people at risk of psychosis: analysis of the EDIE-2 trial

Background Research suggests that the way in which cognitive therapy is delivered is an important factor in determining outcomes. We test the hypotheses in which the development of a shared problem list, use of case formulation, homework tasks and active intervention strategies will act as process variables. Method Presence of these components during therapy is taken from therapist notes. The direct and indirect effect of the intervention is estimated by an instrumental variable analysis. Results A significant decrease in the symptom score for case formulation (coefficient = -23, 95% CI -44 to -1.7, P = 0.036) and homework (coefficient = -0.26, 95% CI -0.51 to -0.001, P = 0.049) is found. Improvement with the inclusion of active change strategies is of borderline significance (coefficient = -0.23, 95% CI -0.47 to 0.005, P = 0.056). Conclusions There is a greater treatment effect if formulation and homework are involved in therapy. However, high correlation between components means that these may be indicators of overall treatment fidelity.