Strong evidence suggests that open access increases the readership of articles but has no effect on the number of citations in the first year after publication. These findings were based on a randomised controlled trial of 11 journals published by the American Physiological Society.
Although we undoubtedly missed a substantial amount of citation activity that occurred after these initial months, we believe that our time frame was sufficient to detect a citation advantage, if one exists. A study of author sponsored open access in the Proceedings of the National Academies of Sciences
reported large, significant differences in only four to 10 months after publication.15
Future analysis will test whether our conclusions hold over a longer observation period.
Previous studies have relied on retrospective and uncontrolled methods to study the effects of open access. As a result they may have confused causes and effects (open access may be the result of more citable papers being made freely available) or have been unable to control for the effect of multiple unmeasured variables. A randomised controlled design enabled us to measure more accurately the effect of open access on readership and citations independently of other confounding effects.
Our finding that open access does not result in more article citations challenges established dogma8 9 10 11 12 13 15
and suggests that the citation advantage associated with open access may be an artefact of other explanations such as self selection.
Whereas we expect a general positive association between readership and citations,14 17 18 19
we believe that our results are consistent with the stratification of readers of scientific journals. To contribute meaningfully to the scientific literature, access to resources (equipment, trained people, and money) as well as to the relevant literature is normally required. These two requirements are highly associated and concentrated among the elite research institutions around the world.7 27
That we observed an increase in readership and visitors to open access articles but no citation advantage suggests that the increase in readership is taking place outside the community of core authors.
Although we need to be careful not to equate article downloads with readership (we have no idea whether downloaded articles are actually read), measuring success by only counting citations may miss the broader impact of the free dissemination of scientific results.
The increase in full text downloads for open access articles in the first six months after publication (fig 2) suggests that the primary benefit to the non-subscriber community is in browsing, as opposed to printing or saving, which would have been indicated by a commensurate increase in PDF downloads. The fact that internet robots were responsible for so much of the initial increase in full text downloads (an additional 83%) compared with PDF downloads (an additional 5%) implies that internet search engines are helping to direct non-subscribers to free journal content. Lastly, the reduction in abstract downloads for open access articles suggests that non-subscribers were probably substituting free full text or PDF downloads (when available) for abstract downloads.
We studied the effect of providing free access to scientific literature directly from the publisher’s website; however, scientific information can be disseminated in many ways. Although the author-pays open access model has received the greatest amount of attention, we should not ignore the many creative access models that publishers use: the delayed access model, with all articles becoming freely available after a defined period after publication; the selective access model, with certain types of articles (for example, original research) being made freely available in subscription access journals; or variations of the models. Most scientific publishers allow authors to post manuscripts of their articles on their own website or in their institution’s digital repository. Funding agencies, such as the National Institutes of Health (United States) and the Wellcome Trust (United Kingdom) have policies for self archiving. One model for publication may not fit the needs of all stakeholders.28
Unanswered questions and future research
The discussion over access and its effects on citation behaviour assumes that articles are read before they are cited. Studies on the propagation of citation errors suggest that many citations are merely copied from the papers of other articles.29 30 31
Given the common behaviour of citing from the abstract (normally available free), the act of citation does not necessarily depend on access to the article. Secondly, the rhetorical dichotomy of “open” access compared with “closed” access does not recognise the degree of sharing that takes place among an informal network of authors, libraries, and readers. Subscription barriers are, in reality, porous.
Our citation counts are limited to those journals indexed by Web of Science. Because this database focuses on covering the core journals in a particular discipline, we missed citations in articles published in peripheral journals.
We measured the number of unique internet protocol addresses as a proxy for the number of visitors to an article. We implied that the difference in number of visitors between open access and subscription based articles (in our case 23%) represents the size of the non-subscriber population. A more direct (although more laborious) method of calculating access by non-subscribers would be to analyse the log transaction files of the publisher and to compare the list of internet protocol addresses from subscribing institutions with the total list of internet protocol addresses. Because of confidentiality issues we did not have access to the raw transaction logs.
Open access articles on the American Physiological Society’s journals website are indicated by an open green lock on the table of contents page. Although icons representing access status are a common feature of most journals’ websites, these may signal something about the quality of the article to potential readers, especially as open access articles have been associated with a large citation advantage.8 9 10 11 12 13 14 15
As a result, readers may have developed a heuristic that associates open access articles with higher quality. This quality signal could have been imparted to those randomly assigned to open access articles in our study and created a positive bias on download counts.
Conversely, we were told by the publisher that most readers never view the table of contents pages. Most people are referred directly to the article by search engines, such as Google, or through the linked references of other articles. Subject indexes, such as PubMed, did not provide an indication of which articles were randomly selected for open access. It is likely that few readers were aware that they were viewing a free article.
Finally, we do not understand whether providing open access to articles had any effect on the behaviour of the authors as they promoted their work to the wider community. We are currently carrying out similar randomised experiments with other journals in an environment where neither authors nor readers are aware of the access status of the article.
Research suggests that a publisher’s web interface can influence the accessibility and use of online articles32 33
; hence we are studying journals published on a single online platform (HighWire Press). We have recently expanded our open access experiment to include an additional 25 journals hosted by HighWire in the disciplines of multidisciplinary sciences, biology, medicine, social sciences, and the humanities. This will allow us to assess whether our results generalise to a broader set of disciplines. We are also observing the performance of 10 control journals that allow author sponsored open access publishing. This will help us to explore which confounding variables may explain the citation advantage that has been widely reported in the literature.
What is already known on this topic
- Studies suggest that open access articles are cited more often than subscription access ones
- These claims have not been validated in a randomised controlled trial
What this study adds
- Open access articles had more downloads but exhibited no increase in citations in the year after publication
- Open access publishing may reach more readers than subscription access publishing
- The citation advantage of open access may be an artefact of other causes