A new analysis has found that the makers of antidepressants such as Prozac and Paxil never published the results of about a third of the drug trials that they conducted to win government approval. This has led to a misleading perception of the drugs’ true effectiveness.

When only published trials are considered, about 60 percent of people taking the drugs report significant relief from depression, compared with roughly 40 percent of those on placebo pills. But when the less positive, unpublished trials are included, the drugs only outperform placebos by a very modest margin.

While 94 percent of positive studies found their way into print, only 14 percent of those with disappointing or uncertain results were published.