Predictors of response to CBT and IPT for depression; the contribution of therapy process
Introduction
The efficacy of Cognitive Behavior Therapy (CBT) and Interpersonal Psychotherapy (IPT) for depression has been demonstrated over many decades of research. Despite this, relatively little is known about the factors that contribute to patients making a positive therapeutic response. Given that only 50–60% of those with depression will benefit from a structured short term therapy, understanding factors that contribute to patient improvement in therapy must remain a research imperative. Clinical characteristics such as high initial depression severity, chronic or recurrent depression, earlier age of onset of depression and comorbid Axis I disorders have all been consistently associated with a poorer response (Blom et al., 2007, Constantino et al., 2008, Frank et al., 2011, Jarrett et al., 1991, Thase et al., 1994). Other factors that have shown some association with a poorer response to therapy include higher levels of dysfunctional attitudes (Jarrett et al., 1991), perfectionism (Enns, Cox, & Pidlubny, 2002), beliefs about the causes of depression (Addis & Jacobson, 1996), and patient expectancy of treatment outcome (Gaston et al., 1989, Ravitz et al., 2011). To date there has been little support for specific therapeutic mechanisms proposed for each therapy, such as cognitive changes for CBT and resolution of interpersonal problems for IPT (Lipstiz and Markowitz, 2013, Longmore and Worrell, 2007). On the contrary, there are some indications that therapy that targets a person's relative strengths rather than deficits is more likely to be beneficial (Cheavens et al., 2010, Imber et al., 1990, Sotsky et al., 1991).
In previous studies, we examined patient predictors of response following weekly sessions of CBT and IPT for depressed outpatients in the Christchurch Psychotherapy for Depression study (CPDS) (Carter et al., 2011, Joyce et al., 2007). Previous analyses of outcome in the CPDS indicated there was no difference in outcome between CBT and IPT (Joyce et al., 2007, Luty et al., 2007). Patient predictors, accounting for about 20% of the variance in response, were the perceived logic of therapy (measured immediately after the first session of therapy), recurrent depression, and childhood reasons for depression (Carter et al., 2011). More specifically, those who believed that the therapy they were about to receive seemed logical, who did not have a recurrent depression and who held moderate (not mild or strong) beliefs that childhood reasons were the cause of their depression had a better response to therapy. Only one differential predictor of treatment response was identified, increasing comorbid personality disorder symptoms were associated with a decrease in response to IPT but not CBT. The average percentage change from pretreatment to post treatment, when more than ten comorbid personality disorder symptoms were present, was 30% for IPT and 58% for CBT, with five to ten comorbid personality disorder symptoms the average percentage change for IPT was 45% and 62% for CBT and with four or fewer comorbid personality disorder symptoms the average percentage change for IPT was 50% and for CBT was 58% (Carter et al., 2011).
Many argue that nonspecific factors or those common to all therapies make the largest contribution to treatment outcome (Goldfried, 2013, Lambert and Barley, 2001, Messer and Wampold, 2002, Safran and Muran, 1995, Wompold, 2001) and that this is where research attention should be directed. Therapist attitudes and behaviours, such as therapist credibility, skills, empathic understanding and affirmation of the patient, have been found to have a positive impact on outcome (Norcross, 2011). In particular, some have proposed that the therapeutic alliance is the most important contributor to therapeutic outcome and is a causal factor in patient improvement (Barber, Connolly, Crits-Cristoph, Gladis, & Siqeuland, 2000). Meta-analyses of the therapeutic alliance–outcome relationship suggest the therapeutic alliance makes a small to moderate contribution (accounting for 5–7% of the variance) to a positive psychotherapy outcome, irrespective of the type of psychotherapy (Castonguay et al., 2006, Horvath et al., 2011, Martin et al., 2000). There is consistent evidence from different lines of research, that patient processes in therapy may be a particularly important determinant of outcome. For example, the patient's contribution to the alliance, as opposed to the therapist's contribution, relates most strongly to outcome (Ablon and Jones, 1999, Stiles et al., 1986). Further, positive patient expectancy (Lambert & Barley, 2001), and patient belief in the treatment rationale (Carter et al., 2006) have been found to be associated with a positive therapy outcome, and poor outcome is consistently predicted by patient unwillingness or inability to become actively involved in therapy (Butler & Strupp, 1986).
The aim of the current study was to examine the added contribution of non-specific therapy process factors measured at three stages (early, middle and penultimate sessions) over the course of therapy to the specific patient predictors of response to therapy previously identified (Carter et al., 2011).
Section snippets
Method
Data for this study came from 165 (males n = 46; females n = 119) of 177 outpatients in the CPDS and for whom Vanderbilt Psychotherapy Process and Vanderbilt Therapeutic Alliance Scale data were available. Participants in the CPDS had a principal current diagnosis of major depressive episode (DSM-IV) and were over the age of 18 years. Participants were required to be free for a minimum of two weeks of any centrally acting drug, except for the occasional hypnotic and the oral contraceptive pill.
Vanderbilt Therapeutic Alliance Scale – revised
The VTAS-R is 37 item modification of the original Vanderbilt Therapeutic Alliance Scale (Krupnick, Sotsky, Watkins, Eklin, & Pilkonis, 1996). The VTAS-R is an observer rated scale with three subscales, therapist contribution, patient contribution and therapist and patient interaction, which can be summed to give a total alliance score. High scores indicate positive therapeutic alliance. Theoretically the VTAS represents a blend of dynamic and eclectic frameworks. The VTAS-R has demonstrated
Results
Demographic and clinical characteristics of the sample can be seen in Table 1. The mean age was 35 years, 44% of the sample was married, and the majority were female and New Zealand European. Approximately 60% had a current comorbid Axis I disorder and the majority of the sample had recurrent depression (74%). Consistent with previous results there was no significant difference between therapies in depression severity prior to or at the end of weekly therapy sessions. In the IPT group mean
Discussion
The current study examined the association of psychotherapeutic factors with outcome during CBT and IPT for depression, and examined the contribution significant psychotherapy process factors made to the previously identified specific patient predictors of outcome. Scores for the Vanderbilt Process Scale and the Vanderbilt Alliance Scale found in the current study were consistent with previous studies in this area (Cecero et al., 2001, Krupnick et al., 1994, Smith et al., 2003). Similarly, the
Funding
This research was funded by grants from the Health Research Council of New Zealand (98/134).
Acknowledgements
Particular thanks to researchers, therapists and clinicians who worked on this study and special thanks to those who participated in the study.
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