(HealthDay News) — The benefits of psychological therapy for depression are overstated, according to research published online September 30 in PLOS ONE.

The researchers analyzed 55 studies funded by the U.S. National Institutes of Health between 1972 and 2008 and concluded that psychological therapy is about 25% less effective than previously thought, The New York Times reported. Specifically, psychological therapy for depression is effective for about 20% of patients, rather than the previous figure of nearly 30%.

Psychological therapy has been regarded as more effective than it actually is partly due to the fact that many studies with poor results were not published in journals, according to study leader Ellen Driessen, of VU University in Amsterdam, and colleagues.

“The efficacy of psychological interventions for depression has been overestimated in the published literature, just as it has been for pharmacotherapy,” the authors write. “Both are efficacious but not to the extent that the published literature would suggest.”

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