Was Eysenck right after all? A reassessment of the effects of psychotherapy for adult depression.

P Cuijpers,D D Ebert,E Karyotaki,M Reijnders

doi:10.1017/s2045796018000057

P Cuijpers, D D Ebert + Show 2 more

Open Access

https://doi.org/10.1017/s2045796018000057

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Abstract

In the 1950s, Eysenck suggested that psychotherapies may not be effective at all. Twenty-five years later, the first meta-analysis of randomised controlled trials showed that the effects of psychotherapies were considerable and that Eysenck was wrong. However, since that time methods have become available to assess biases in meta-analyses. We examined the influence of these biases on the effects of psychotherapies for adult depression, including risk of bias, publication bias and the exclusion of waiting list control groups. The unadjusted effect size of psychotherapies compared with control groups was g = 0.70 (limited to Western countries: g = 0.63), which corresponds to a number-needed-to-treat of 4.18. Only 23% of the studies could be considered as a low risk of bias. When adjusting for several sources of bias, the effect size across all types of therapies dropped to g = 0.31. These results suggest that the effects of psychotherapy for depression are small, above the threshold that has been suggested as the minimal important difference in the treatment of depression, and Eysenck was probably wrong. However, this is still not certain because we could not adjust for all types of bias. Unadjusted meta-analyses of psychotherapies overestimate the effects considerably, and for several types of psychotherapy for adult depression, insufficient evidence is available that they are effective because too few low-risk studies were available, including problem-solving therapy, interpersonal psychotherapy and behavioural activation.

Highlights

It is 65 years ago that Eysenck wrote an influential paper that shocked the community of psychotherapists
Based on naturalistic studies and a small sample of outcome studies, Eysenck said that the majority of patients with mental health problems get better anyway, whether or not they are treated with psychotherapy
The overall pooled effect size for all psychotherapies compared with any control group (k = 369) was g = 0.70, which corresponds with an NNT of 4.18 (Table 1)

Summary

Introduction

It is 65 years ago that Eysenck wrote an influential paper that shocked the community of psychotherapists. Since the publication of Eysenck’s paper, some smaller reviews of controlled studies wanted to refute Eysenck’s conclusion and tried to show that psychotherapy did have an effect of the mental health of patients (Bergin & Lambert, 1971; Luborsky et al 1975). These were small review papers, using the voting method (in which the number of studies with positive effects is counted), and the results could not be used as strong evidence for positive effects of psychotherapy and against Eysenck’s conclusions. He calculated the effects in terms of standard deviations (effect sizes), which is not depending on the type of outcome measure; and by weighing the studies by sample size (larger studies contribute more to the pooled outcome), they made it possible to integrate all these studies into one overall estimate of the effect size on an intervention

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