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Clinical Psychology: Evolving Theory, Practice, and Research

General Findings The meta-analysis by Elliott et al. (2013) is the largest and most comprehensive review of humanistic-experiential psychotherapies (HEP) to date. The review included a total of 14,206 individuals, with 62 studies compared to wait-list/control (31 of which were RCTs), and 135 studies directly comparing HEP to other therapies (82 of which were RCTs). The average length of treatment was 20 sessions. Elliott et al. (2013) combined random effects model significance testing (Wilson & Lipsey, 2001) with equivalence analysis, allowing them to demonstrate the relative levels of equivalence between HEP and non-HEP approaches. They adopted the following conventions for interpreting the practical or clinical implication of differences in effect size: “Equivalent”: within .1 standard deviation of zero (greater than –.1 and less than .1); “Trivially Different”: between .1 and .2 standard deviation from zero; “Equivocal”: between .2 and .4 standard deviation from zero; “Clinically Better/Worse”: at least .4 standard deviation from zero. These criteria for comparing treatment effects are used across the meta-analysis. Overall, pre-post effect sizes were large (d = .96). Weighted effect size for studies with a control group remained large (dw = .76), a finding which remained consistent in randomised samples. These findings indicate that approximately 80% of pre-post gains can be attributed to experiential therapy. Effect size differences between therapies were non-significant (-.02) in treatment comparison studies. Equivalence analyses revealed that HEP therapies were ‘equivalent’ to other approaches in general, however when compared to CBT interventions HEP obtained ‘trivially worse’ therapy outcomes (-.13). By contrast, HEP studies showed ‘trivially better’ (.17) effect sizes when compared to approaches other than CBT. Researcher allegiance favoured HEPs in 65% of studies, however in studies with treatment comparisons, the allegiance was significantly lower at just 31% pro-HEP. This finding must be seen in the context of researchers from other theoretical orientations using relationship control conditions which tend to be labelled as ‘supportive’ or ‘non-directive’ therapy. The contribution of researcher allegiance has been found to represent a moderate and consistent effect on psychotherapy outcome studies across meta-analyses (Munder, Brütsch, Leonhart, Gerger, & Barth, 2013). Compounding this issue, allegiance often goes unreported in meta-analyses and only a tiny fraction of RCTs (3.2%) report it (Dragioti, Dimoliatis, & Evangelou, 2015). When equivalence analyses were repeated controlling for researcher allegiance, Elliott et al. (2013) found that all differences between therapies were reduced to ‘equivalent’ effect sizes (dw = -.03 to .06).