Evidence Based Treatment - interesting facts
In psychology and in medicine more generally, meta-analysis is a widely accepted method for summarizing and synthesizing the ﬁndings of independent studies (Lipsey & Wilson, 2001; Rosenthal, 1991; Rosenthal & DiMatteo, 2001). Meta-analysis makes the results of different studies comparable by converting ﬁndings into a common metric, allowing findings to be aggregated or pooled across studies. A widely used metric is effect size, which is the difference between treatment and control groups, expressed in standard deviation units. An effect size of 1.0 means that the average treated patient is one standard deviation healthier on the normal distribution or bell curve than the average untreated patient. An effect size of 0.8 is considered a large effect in psychological and medical research, an effect size of 0.5 is considered a moderate effect, and an effect size of 0.2 is considered a small effect (Cohen, 1988). The first major meta-analysis of psychotherapy outcome studies included 475 studies and yielded an overall effect size (various diagnoses and treatments) of 0.85 for patients who received psychotherapy compared with untreated controls (Smith, Glass, & Miller, 1980). Subsequent meta-analyses have similarly supported the efﬁcacy of psychotherapy. The influential review by Lipsey and Wilson (1993) tabulated results for 18 meta-analyses concerned with general psychotherapy outcomes, which had a median effect size of 0.75. It also tabulated results for 23 metaanalysis concerned with outcomes in CBT and behavior modiﬁcation, which had a median effect size of 0.62. A meta-analysis by Robinson, Berman, and Neimeyer (1990) summarized the ﬁndings of 37 psychotherapy studies concerned speciﬁcally with outcomes in the treatment of depression, which had an overall effect size of 0.73. These are relatively large effects. (For a review of psychotherapy efﬁcacy and effectiveness research, see Lambert & Ogles, 2004). To provide some points of reference, it is instructive to consider effect sizes for antidepressant medications. An analysis of U.S. Food and Drug Adminstration (FDA) databases (published and unpublished studies) reported in the New England Journal of Medicine found effect sizes of 0.26 for ﬂuoxetine (Prozac), 0.26 for sertraline (Zoloft), 0.24 for citalopram (Celexa), 0.31 for escitalopram (Lexapro), and 0.30 for duloxetine (Cymbalta). The overall mean effect size for antidepressant medications approved by the FDA between 1987 and 2004 was 0.31 (Turner, Matthews, Linardatos, Tell, & Rosenthal, 2008).3 A meta-analysis reported in the prestigious Cochrane Library (Moncrieff, Wessely, & Hardy, 2004) found an effect size of 0.17 for tricyclic antidepressants compared with active placebo (an active placebo mimics the side effects of an antidepressant drug but is not itself an antidepressant).4 These are relatively small effects. Methodological differences between medication trials and psychotherapy trials are sufﬁciently great that effect sizes may not be directly comparable, and the ﬁndings should not be interpreted as conclusive evidence that psychotherapy is more effective. Effect sizes for antidepressant medications are reported to provide reference points that will be familiar to many readers (for more comprehensive listings of effect size reference points, see, e.g., Lipsey & Wilson, 1993; Meyer et al., 2001).
Especially noteworthy is the recurring fnding that the benefits of psychodynamic therapy not only endure but increase with time, a finding that has now emerged from at least ﬁve independent meta-analyses (Abbass et al., 2006; Anderson & Lambert, 1995; de Maat et al., 2009; Leichsenring & Rabung, 2008; Leichsenring et al., 2004). In contrast, the beneﬁts of other (nonpsychodynamic) empirically supported therapies tend to decay over time for the most common disorders (e.g., depression, generalized anxiety; de Maat, Dekker, Schoevers, & de Jonghe, 2006; Gloaguen, Cottraux, Cucharet, & Blackburn, 1998; Hollon et al., 2005; Westen, Novotny, & ThompsonBrenner, 2004).
Jonathan Shedler University of Colorado Denver School of Medicine