Freely-accessible articles are cited more frequently, but open access is not the cause, a new study reports.
The article, “Does Open Access in Ophthalmology Affect How Articles are Subsequently Cited in Research?“ will be published in Ophthalmology, a journal of the American Academy of Ophthalmology.
The study reports an analysis of citation counts to 895 articles published in six ophthalmology journals (three open access journals and three journals employing some form of subscription access). All articles were published in 2003.
Open access journals were paired with subscription-access journals with equivalent impact factors. It’s the first study to use such a journal pairing methodology.
In addition, the researchers used two citation databases ( and Google Scholar) to count citations to each article. A large citation advantage in favor of open access articles suggests that the subscription publishing model inhibits the dissemination of scientific knowledge.
The authors report that raw citation comparisons of the two cohorts of articles were consistent with early citation studies: open access articles received between one-third (Scopus) and two-thirds (Google Scholar) more citations than their subscription-based counterparts. However, a more robust analysis revealed that the reasons for the increase were not attributed to access models. The researchers write:
access was not a significant factor in the explanation of the number of times an article was subsequently cited. Rather, number of authors, the country/region in which the article was published, language, funding, and subject of the article were found to be significant variables.
In other words, open access articles were cited more frequently, but not because they were freely available. The authors explain the meaning of their results:
Why, then, is open access not an important factor in ophthalmology? One could argue that academic researchers and clinicians at large institutions in Western countries have access to the majority of articles in the literature because their institutions or libraries have arrangements with publishers.
While the authors of this paper do not focus on the potential benefits of freely accessible medical information to those outside the research community, this article builds upon a growing wealth of evidence suggesting that the so-called “open access citation advantage” is merely a spurious relationship.
It should serve as a gentle reminder that correlation does not equal causation.