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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 (Scopus 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.

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Phil Davis

Phil Davis

Phil Davis is an independent researcher and publishing consultant specializing in the statistical analysis of citation, readership, publication and survey data. He has a Ph.D. in science communication from Cornell University (2010), extensive experience as a science librarian (1995-2006) and was trained as a life scientist. His research has focused on the on the dissemination of scientific information, rewards and incentives in academic publishing, and economic issues related to libraries, authors and publishers.

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6 Thoughts on "Open Access Not the Focus in Ophthalmology"

Would you like to expand on “growing wealth of evidence”?

The authors’ conclusion does not accord with the idea that their result is general: “Unlike other fields of science, open access thus far has not affected how ophthalmology articles are cited in the literature.”

For an example of a different result, suggesting that open access via self-archiving does enhance citations in agricultural research, see http://iaald.blogspot.com/2009/07/open-access-enhances-accessibility-and.html .

Dear Jim,
Below are citations to some articles which dispute access being a contributing cause of the citation advantage:

Kurtz, M. J., Eichhorn, G., Accomazzi, A., Grant, C., Demleitner, M., Henneken, E., et al. (2005). The effect of use and access on citations. Information Processing and Management, 41, 1395-1402. http://arxiv.org/abs/cs/0503029v1

Kurtz, M. J., & Henneken, E. A. (2007). Open Access does not increase citations for research articles from The Astrophysical Journal: Harvard-Smithsonian Center for Astrophysics. http://arxiv.org/abs/0709.0896

Moed, H. F. (2007). The effect of ‘Open Access’ upon citation impact: An analysis of ArXiv’s Condensed Matter Section. Journal of the American Society for Information Science and Technology, 58(13), 2047-2054. http://arxiv.org/abs/cs/0611060v1

Davis, P. M., Lewenstein, B. V., Simon, D. H., Booth, J. G., & Connolly, M. J. L. (2008). Open access publishing, article downloads and citations: randomised trial. BMJ, 337, a568. http://dx.doi.org/10.1136/bmj.a568

Gaulé, P., & Maystre, N. (2008). Getting cited: does open access help? : CEMI Working Paper 2008-007. http://ilemt.epfl.ch/repec/pdf/cemi-workingpaper-2008-007.pdf

Michael J Kurtz (in a recent talk I attended) pointed out that in fields such as ophthalmology, there are many users of the articles who do not create new citations. In the fields he’s studied, usages follow citations (the curves are basically the same shape, just shifted). I’m not really surprised that OA hasn’t increased citations, but maybe that’s not the question for ophthalmology. Maybe the question for fields with clinicians/practitioners is if OA increases usage.

Very good point. The Davis et al. study [1] measures both readership (as article downloads) and citations. While it does not report a difference in citation frequency to freely-available articles, it does demonstrate that freely-accessible articles receive significantly more downloads and unique visitors. Many of these downloads, however, can be the result of indexing robots (like Google).

There is no doubt that medical fields like ophthalmology have many practitioners who read — but do not contribute to — the literature. Much more work needs to be done on this front.

I think we can conclude that if there is an “open access citation advantage” it is indeed very small and not nearly in the same range (200%-700%) promoted in the earlier studies.

[1] Davis, P. M. et al. (2008). Open access publishing, article downloads and citations: randomised trial. BMJ, 337, a586. http://dx.doi.org/10.1136/bmj.a568

I know of only one study to date which looks at the effect of freely-accessible medical literature on medical practice.


David J. Hardisty, D. A. F. H. (2008). Diffusion of treatment research: does open access matter? Journal of Clinical Psychology, 64(7), 821-839. http://dx.doi.org/10.1002/jclp.20492

Advocates of the Open Access movement claim that removing access barriers will substantially increase the diffusion of academic research. If successful, this movement could play a role in efforts to increase utilization of psychotherapy research by mental health practitioners. In a pair of studies, mental health professionals were given either no citation, a normal citation, a linked citation, or a free access citation and were asked to find and read the cited article. After 1 week, participants read a vignette on the same topic as the article and gave recommendations for an intervention. In both studies, those given the free access citation were more likely to read the article, yet only in one study did free access increase the likelihood of making intervention recommendations consistent with the article.

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