Are improvements in cognitive content and depressive symptoms correlates or mediators during acute-phase cognitive therapy for recurrent major depressive disorder?

The cognitive model of depression posits that cognitive therapy's (CT) effect on depressive symptoms is mediated by changes in cognitive content (e.g., automatic negative thoughts, dysfunctional attitudes, failure attributions). We tested improvement and normalization of cognitive content among outpatients (N = 523) with recurrent major depressive disorder treated with acute-phase CT (Jarrett & Thase, 2010; Jarrett, Minhajuddin, Gershenfeld, Friedman, & Thase, 2013). We also tested whether improvement in cognitive content accounted for subsequent changes in depressive symptoms and vice versa. Five measures of content improved substantively from pre- to post-CT (median d = 0.96), and the proportions of patients scoring in “healthy“ ranges increased (median 45% to 82%). Evidence for cognitive mediation of symptom reduction was limited (median r =.06), as was evidence for symptom mediation of cognitive content improvement (median r =.07). We discuss measurement and design issues relevant to detection of mediators and consider alternative theories of change.