Does Publication Bias Inflate the Apparent Efficacy of Psychological Treatment for Major Depressive Disorder? A Systematic Review and Meta-Analysis of US National Institutes of Health-Funded Trials

Abstract

Background: The efficacy of antidepressant medication has been shown empirically to be overestimated due to publication bias, but this has only been inferred statistically with regard to psychological treatment for depression. We assessed directly the extent of study publication bias in trials examining the efficacy of psychological treatment for depression.

Methods and findings: We identified US National Institutes of Health grants awarded to fund randomized clinical trials comparing psychological treatment to control conditions or other treatments in patients diagnosed with major depressive disorder for the period 1972-2008, and we determined whether those grants led to publications. For studies that were not published, data were requested from investigators and included in the meta-analyses. Thirteen (23.6%) of the 55 funded grants that began trials did not result in publications, and two others never started. Among comparisons to control conditions, adding unpublished studies (Hedges' g = 0.20; CI95% -0.11~0.51; k = 6) to published studies (g = 0.52; 0.37~0.68; k = 20) reduced the psychotherapy effect size point estimate (g = 0.39; 0.08~0.70) by 25%. Moreover, these findings may overestimate the "true" effect of psychological treatment for depression as outcome reporting bias could not be examined quantitatively.

Conclusion: The efficacy of psychological interventions for depression has been overestimated in the published literature, just as it has been for pharmacotherapy. Both are efficacious but not to the extent that the published literature would suggest. Funding agencies and journals should archive both original protocols and raw data from treatment trials to allow the detection and correction of outcome reporting bias. Clinicians, guidelines developers, and decision makers should be aware that the published literature overestimates the effects of the predominant treatments for depression.

Fig 1. PRISMA flow chart of grants identified and the extent to which these led to publications.

Note: MDD = major depressive disorder; NIH = US National Institutes of Health; RCT = randomized clinical trial.

Fig 2. Psychological treatment versus control conditions (all).

Note: Not all results of the unpublished studies are presented at study level, because we did not have permission of the investigators to do so. BDI = Beck Depression Inventory; CTRL-NS = non-specific control condition (psychological placebo); CTRL-NS(PLAC) = pill-placebo control condition; CTRL-NT = no-treatment control condition; CTRL-TAU = treatment as usual control condition; HAMD = Hamilton Depression Rating Scale; PT = psychological treatment; SCL-90-D = Symptom Checklist—90 item, depression subscale.

Fig 3. Psychological treatment versus no-treatment control conditions.

Note: Not all results of the unpublished studies are presented at study level, because we did not have permission of the investigators to do so. CTRL-NT = no-treatment control condition; PT = psychological treatment; SCL-90-D = Symptom Checklist—90 item, depression subscale.

Fig 4. Psychological treatment versus treatment control conditions.

Note: Not all results of the unpublished studies are presented at study level, because we did not have permission of the investigators to do so. BDI = Beck Depression Inventory; CTRL-NS = non-specific control condition (psychological placebo); CTRL-NS(PLAC) = pill-placebo control condition; CTRL-TAU = treatment as usual control condition; HAMD = Hamilton Depression Rating Scale; PT = psychological treatment.

Fig 5. Psychological treatment versus other psychological treatment.

Note: Not all results of the unpublished studies are presented at study level, because we did not have permission of the investigators to do so. BDI = Beck Depression Inventory; HAMD = Hamilton Depression Rating Scale; PT = psychological treatment.

Fig 6. Psychological treatment versus antidepressant medication.

Note: Not all results of the unpublished studies are presented at study level, because we did not have permission of the investigators to do so. ADM = antidepressant medication; HAMD = Hamilton Depression Rating Scale; PT = psychological treatment.

Fig 7. Psychological treatment combined with antidepressant medication versus antidepressant medication monotherapy.

Note: Not all results of the unpublished studies are presented at study level, because we did not have permission of the investigators to do so. ADM = antidepressant medication; HAMD = Hamilton Depression Rating Scale; IDS-C30 = Inventory of Depressive Symptomatology– 30-item Clinician Rated version; PT = psychological treatment.