A new study published in the journal PLOS ONE has revealed that a combined therapy of medications and psychological talks help patients suffering from depression, but adopting psychological therapy alone may work, but never so effectively.

The new study reveals that any effectiveness ascribed to applying psychological therapy to depression is simply overstated.

The researchers analyzed 55 earlier studies conducted between 1972 and 2008 and funded by the US National Institutes of Health before concluding that psychological therapy is actually 25% less effective than earlier believed.

The leader of the study, Ellen Driessen, together with other colleagues from VU University of Amsterdam noted that other researchers have always overrated the roles played by psychological therapy in depression because studies with poor results were not published in peer-reviewed journals.

Driessen and her collaborators estimate that the effectiveness of psychological therapy for treating depression has been proven in 20% of patients, but never in 30% of patients has earlier reported in past studies.

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

Further studies revealed that publication bias has been responsible for overstating the effectiveness of antidepressant medications, even though this only applies to psychological therapy used for depression treatments.

To this end, researchers have always wanted to know how publication bias impacted on rating the efficacy of studies relating to psychological treatment for depression, and this was trialled out while conducting pertinent studies into health phenomena.

Co-author Erick Turner, an associate professor of psychiatry and pharmacology at OHSU School of Medicine stated that this current study shows that publication bias occurs in psychotherapy, mirroring what researchers have always known to transpire with antidepressants and other drugs.

Ultimately, researchers of the current study advise publication journals and organizations that fund scientific and health research to archive published and unpublished findings so that reporting bias can be easily detected and corrected in time.