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.