Open access papers attract up to a fifth more citations than those locked away in closed journals, a new study has found.

Jim Ottaviani, librarian at the University of Michigan, looked at what happened when his institution made papers available through its repository and found that “an open access citation advantage as high as 19 per cent exists”.

And better-cited papers gained more from being open access, found “The Post-Embargo Open Access Citation Advantage: It Exists (Probably), It’s Modest (Usually), and the Rich Get Richer (of Course)”, published in Plos One. “When an article benefits from being OA, it benefits a lot,” the paper concludes.

Previous studies that attempted to determine whether an open access citation advantage exists have been dogged by the difficulty of finding comparable samples of open-access and subscription-only articles.

For example, it could be that authors select only their best articles to be made public in an otherwise closed journal by paying an article processing charge, meaning they get more citations regardless of the publishing format.

The study got around this problem by looking at the citation rates of thousands of articles after they had been made public through Michigan’s repository over the past decade. This meant that Mr Ottaviani had a relatively random sample of nearly 4,000 open access papers across a range of otherwise subscription-only journals.

It looked at papers that had been made open access only in a university repository (so-called green open access). Although these articles are normally easy to find via search engines, had they been made open access through their journal (referred to as gold open access), they might have garnered even more citations, the paper points out.

Although the paper finds that a citation advantage exists, it is smaller than in some other studies that have looked at the same question, and found that open access boosts citations by up to 172 per cent.

SPARC Europe, an organisation made up of European university libraries and research institutes that campaigns for research openness, has collated 70 studies that looked at whether open access provides a citation advantage and found that 46 of them did.

That paper concludes by recommending a new study involving a greater mix of subjects (Mr Ottaviani’s paper looked mainly at physical science, health science and engineering articles) and more than one university, which it says would produce even more robust results.

david.matthews@tesglobal.com