Science is based on evidence. So is the evaluation of open access. Many people want full-text journal articles to be available free online, but is it necessary to provide them? Can open access increase the visibility of work published in a journal? Many studies are trying to answer such questions.

Jocalyn Clark, of PLoS Medicine, provided an overview of open access and summarized trends in current research on the subject. She said that it is believed that open access can facilitate the dissemination of research, encourage global inclusion and participation, bridge the knowledge divide, and remove access barriers.

She also made the following points: Many scientific studies are funded by taxes, and taxpayers have a right to free access to the results of the studies. Also, open access can ease the burden of libraries and save them the cost of maintaining journal subscriptions.

Most research on open access, Clark said, now employs some or all of the following criteria to measure the impact of open access: number of citations, downloads or use of articles, globalization of publications, economic indicators, and impact on policy or clinical practice. However, more research is needed, she said. For example, researchers need to define more specifically what the “impact” of open access is and how it affects other researchers, publishers, and the government. More research is needed to understand how open access accelerates the advancement of science and how it affects the making of policy, such as health policy.

Tim Ingoldsby, of the American Institute of Physics, said that he was studying the pervasiveness of deposits to the preprint server arXiv.org in physics publishing. Before 1991, the distribution of preprints of physics research articles was slow because it depended on the mail and was confined to major research institutions. After 1991, the implementation of FTP servers and later Web servers led to a steady increase in preprint availability.

Ingoldsby conducted research on arXiv. org from summer 2008 to April 2009. He found that the percentage of research articles published in research journals that had previously been deposited to arXiv.org varied among fields of physics.

He also found that physicists were not frequently updating their arXiv.org deposits to add information from published versions of their papers. Some editors changed titles of manuscripts more often than expected, and he said that this made his research project much more difficult to complete because it was harder to verify that a preprint from particular authors was the same paper published in a journal under a different title.

Ingoldsby said that he would extend his study to include more physics journals and to obtain better statistics on the use of arXiv.org by practitioners in various subfields.

Philip Davis, a doctoral student at Cornell University, presented the results of several randomized controlled studies of effects of open-access publishing on readership and citations. He began by discussing research methods and how early studies of the association between access and citations may be prone to systematic bias.

To minimize bias, Davis and his colleagues conducted a randomized controlled trial on 11 research journals published by the American Physiological Society. The study was expanded to include journals published by other scientific societies, including Science, The FASEB Journal, Genetics, and five journals published by the American Heart Association. On publication, articles were randomly assigned to either the treatment group (free access) or the control group (subscription access). Davis and his colleagues then collected data on the number of times that each article was downloaded and the number of times that it was cited. They found that although freely accessible articles were downloaded many more times, they were not cited more frequently. Davis concluded that although making the scientific literature freely available may have benefits, an increase in citations appears not to be one of them.