The effect of cognitive behavioral treatment on the positive symptoms of schizophrenia spectrum disorders: A meta-analysis
Introduction
Despite the proven efficacy of anti-psychotic drugs, a substantial proportion of patients (10–60%) experience medication-resistant positive symptoms (Lindenmayer, 2000). Adjunctive psychological treatments that can improve outcome are clearly needed. Based on earlier case reports (Beck, 1952), specialized cognitive behavioral approaches have been developed to decrease patient's distress associated with hallucinations and delusions (Haddock et al., 1998) and these may be useful as adjunctive treatments.
Three recent meta-analyses have confirmed that cognitive behavioral therapy (CBT) produces promising clinical effect on patients with schizophrenia spectrum disorders (Gould et al., 2001, Pilling et al., 2002, Rector and Beck, 2001). In the first empirical review, Gould et al. (2001) indicated that the mean effect size of CBT in reducing psychotic symptoms was 0.65 (95% CI = 0.56–0.71) across seven controlled trials including 340 patients. Moreover, follow-up analyses in four studies showed that patients continued to improve over time (Mean ES = 0.93). However, Gould and colleagues conducted statistical analysis on effect sizes without taking sample size into account. However, effect sizes based on large samples should play a bigger role in any statistical analysis than those based on smaller samples (Lipsey and Wilson, 2001, Shadish and Haddock, 1994). In a second meta-analysis of seven randomized clinical trials (RCTs) involving 383 subjects, group contrast analysis in six of the seven studies demonstrated a large effect size in favor of CBT (Mean weighted ES = 0.91, SD = 0.14) (Rector and Beck, 2001). However, results of Beck's study rely only on six studies (including 239 patients) and among them were two with methodological limitations (absence of blind rating) that report very large effect sizes (> 0.75) in favor of CBT (Drury et al., 1996, Pinto et al., 1999). Finally, in a more recent meta-analysis of eight RCTs including 393 patients, Pilling et al. (2002) concluded on the basis of four suitable trials (273 patients) that CBT produce clear improvements in mental state (Pooled fixed effect odds ratio = 0.27; 95% CI = 0.15–0.49) compared to all other treatments. This very rigorous meta-analysis provides promising results but unfortunately did not focus on the improvement in positive symptoms. Furthermore, Pilling et al. (2002) did not include three eligible trials. The first trial was probably excluded because of the absence of randomization (Garety et al., 1994). Surprisingly, two other studies were not included although continuous mental state data were available (Pinto et al., 1999, Tarrier et al., 1993).
Despite these encouraging results, the issue about CBT efficacy in the treatment of patients suffering from psychotic disorders remains an open question (Turkington et al., 2003). Furthermore, the Cochrane library (Cormac et al., 2003) stated that CBT may be of interest, but that other approaches, perhaps more widely available, are just as effective. Recently, numerous controlled trials have been completed and thus, it is useful to further examine the effects of CBT now that more patients have been included in trials. The majority of the trials of CBT have been conducted with chronic out-patients suffering from persistent residual psychotic symptoms. However, results of three studies have now been published in which CBT was used with sample of in-patients suffering from an acute psychotic episode (Drury et al., 1996, Lewis et al., 2002, Startup et al., 2004). Furthermore, a number of trials have included in addition to TAU non-specific interventions as a separate treatment limb to control for common effects of psychological treatment. Thus, it would be interesting to examine the effects of CBT related to psychotic status of patients (chronic condition, acute episode) and type of control conditions (treatment as usual, non-specific intervention, waiting-list). To address these issues, we conducted a meta-analysis to measure the efficacy of CBT in the treatment of positive symptoms in schizophrenia spectrum disorders.
Section snippets
Literature searches
Comprehensive searches of the psychological literature in PsycInfo, Medline, CINHAL and Francis databases were conducted as well as studies mentioned in books. We obtained article abstracts by cross referencing the following key search words: schizophrenia, psychosis, cognitive behavioral therapy, CBT and controlled trial. We examined the reference sections of all retrieved studies, as well as in a set of standard books on CBT.
Selection of studies
The search produced fifty-three studies. These identified studies
Results
Fifteen studies involving 1504 patients (68.1% of male, mean age of 36.02 years, SD = 4.53) met the criteria for inclusion in this analysis. Sufficient data to compute effect size were available from twelve published articles. For the remaining three studies (Haddock et al., 1999, Trower et al., 2004, Turkington et al., 2002), authors were contacted by e-mail. Because appropriate data were not available from the authors, one study was excluded. Table 1 provides an overview of descriptive
Discussion
This review provides effect size analyses for controlled studies of cognitive behavioral treatments of positive symptoms in schizophrenia spectrum disorders published during the last 15 years. This meta-analysis using a sample of 14 outcome published studies supports the general conclusion that CBT is a promising approach for adjunctive treatment of positive symptoms in patients with schizophrenia. Moreover, the therapeutic effects are preserved at follow-up, suggesting that the CBT has
Acknowledgements
We thank Kerry Ross and Douglas Turkington for providing data.
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