Scientific literature appears to be biased when it comes to reporting the benefits of psychotherapy as a treatment for depression.

That’s the conclusion of a study published in the journal PLOS ONE. It is the follow-up to a study published in 2008 that created a considerable stir when it found a comparable publication bias in scientific articles reporting the efficacy of antidepressant drugs.

Says Steven Hollon, a psychology professor at Vanderbilt University who co-authored the study with colleagues from Oregon Health and Science University, VU University Amsterdam, and the University of Groningen:

“This doesn’t mean that psychotherapy doesn’t work. Psychotherapy does work. It just doesn’t work as well as you would think from reading the scientific literature.”

The basic problem arises because clinical studies of the treatments for depression with more positive outcomes are more likely to be published than studies with less favorable results.

“It’s like flipping a bunch of coins and only keeping the ones that come up heads,” says Hollon.

The research team identified all the US National Institutes of Health grants awarded to fund clinical trials of psychological treatments for depression from 1972 to 2008. They found that nearly a quarter of these grants (13 of 55) had not published trial results.

Publication Bias

They contacted the researchers who had conducted the 13 unpublished studies and requested the results from their studies. Using the unpublished data together with the published data, they conducted a series of meta-analyses from which they concluded that psychotherapy works, but that its effectiveness was inflated by publication bias.

“This study shows that publication bias occurs in psychotherapy, mirroring what we’ve seen previously with antidepressants and other drugs,”

says co-author Erick Turner, associate professor of psychiatry and pharmacology at OHSU School of Medicine, who directed the 2008 study of antidepressants.

A question that was raised, but not answered, by that study was whether it was reasonable to recommend psychotherapy over drug treatment without examining whether publication bias might be occurring with psychotherapy, too.

“Journal articles are vetted through the process of peer review, but this process has loopholes, allowing treatment benefits to be overstated and potential harms to be understated,” Turner says. “The consumers of this skewed information are health care providers and, ultimately, their patients.”

The authors suggest that both the funding agencies and the journals should archive the original proposals and raw data from the trials—both published and unpublished—so that this form of reporting bias can be detected and corrected in the future.

Driessen E, Hollon SD, Bockting CLH, Cuijpers P, Turner EH (2015) 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 PLoS ONE 10(9): e0137864. doi:10.1371/journal.pone.0137864

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