In the continuing debate about open access to scientific literature, the pro-access side gained strength with a study, published this afternoon, that says that, during the first four to 16 months after publication, papers with free access get cited more often than those that require subscriptions. The study appears in an open-access journal, PLoS Biology, and was written by Gunther Eysenbach, of the University of Toronto, who also edits another open-access journal, the Journal of Medical Internet Research.

The study is the first to compare open-access and non-open-access papers from the same journal. Mr. Eysenbach compared papers published in the journal Proccedings of the National Academy of Sciences in the latter half of 2004. That journal began in June 2004 to offer authors the option of paying $1,000 to make their articles free online upon publication. If authors did not pay the extra fee, their papers remained password-protected for the first six months after publication.

Mr. Eysenbach found that the open-access papers were twice as likely as the password-protected articles to be cited four to 10 months after publication, and almost three times as likely from 10 to 16 months afterward. Not yet clear is whether the open-access advantage increases citation in the long run or whether the trend is similar for other journals.

The open-access movement has drawn additional strength in recent months from pressure in Congress to make taxpayer-supported research freely available (The Chronicle, May 3) and from the European Commission (The Chronicle, April 19).