The makers of antidepressants like Prozac and Paxil never published the results of about a third of the drug trials that they conducted to win government approval, misleading doctors and consumers about the drugs’ true effectiveness, a new analysis has found.

In published trials, 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 But when the less positive, unpublished trials are included, the advantage shrinks: the drugs outperform placebos, but by a modest margin, concludes the new report, which appears Thursday in The New England Journal of Medicine.

Previous research had found a similar bias toward reporting positive results for a variety of medications; and many researchers have questioned the reported effectiveness of antidepressants. But the new analysis, reviewing data from 74 trials involving 12 drugs, is the most thorough to date. And it documents a large difference: while 94 percent of the positive studies found their way into print, just 14 percent of those with disappointing or uncertain results did.

The finding is likely to inflame a continuing debate about how drug trial data is reported. In 2004, after revelations that negative findings from antidepressant trials had not been published, a group of leading journals agreed to stop publishing clinical trials that were not registered in a public database. Trade groups representing the world’s largest drug makers announced that members’ companies would begin to release more data from trials more quickly, on their own database, clinicalstudyresults.org.