Loughborough University Institutional Repository

Four subjects, ecology, applied mathematics, sociology and economics, were selected to assess whether there is a citation advantage between journal articles that have an open access (OA) version on the Internet compared to those articles that are exclusively toll access (TA). Citations were counted using the Web of Science and the OA status of articles was determined by searching OAIster, OpenDOAR, Google and Google Scholar. Of a sample of 4633 articles examined, 2280 (49%) were OA and had a mean citation count of 9.04, whereas the mean for TA articles was 5.76. There appears to be a clear citation advantage for those articles that are OA as opposed to those that are TA. This advantage, however, varies between disciplines, with sociology having the highest citation advantage but the lowest number of OA articles from the sample taken and ecology having the highest individual citation count for OA articles but the smallest citation advantage. Tests of correlation or association between OA status and a number of variables were generally found to be weak or inconsistent. The cause of this citation advantage has not been determined. Introduction Academics are frequently judged, in part at least, on the quality of their published research. The greater the impact of that research as counted by, for example, the number of citations it receives, the better, it is believed, is the quality of the work (van Leeuwen et al. 2003, pp. 262-263). Receiving many citations for academic research generally correlates strongly with academic success; an analysis of Nobel laureates and their citation counts by Garfield (1979, pp. 63-64) and Opthof (1997, p. 2), although tenuous, gives some credibility to the idea that the two are linked. Likewise a similar ranking by Hirsch (2007, pp. 16569-16572) using his h-index, which uses This article was accepted for publication: NORRIS, M., OPPENHEIM, C. and FYTTON, R., 2008. The citation advantage of openaccess articles. Journal of the American Society for Information Science and Technology, 59 (12), pp. 1963-1972 [© 2008 ASIS&T]. The definitive version is available at: http://www3.interscience.wiley.com/journal/117946195/grouphome/home.html article citation counts, has been successfully used to identify and rank prominent physicists. In recent years, it has become possible for authors to self-archive an electronic version of their work in a variety of locations from personal web pages, to a disciplinary archive or to an institutional repository. In so doing, authors make their work open access (OA) and freely available to anyone who has Internet access. Toll access (TA) articles (often known as closed access articles) remain behind subscription barriers and are only accessible by a personal or institutional subscription. If it can be shown that self-archived OA research often receives more citations than closed access research, then a convincing argument can be made to persuade researchers to selfarchive their work. A number of studies (Antelman, 2004; Eysenbach, 2006; Harnad & Brody, 2004; Lawrence, 2001) have shown that those authors who make their work OA will receive more citations and hence achieve greater impact than those authors whose articles remain behind subscription barriers. Despite this advantage, few authors, however, self-archive their work (Swan & Brown, 2005, pp. 62-68); the selfarchiving rate of authors seems to be at best, around 15% (Hajjem et al. 2005; Sale, 2005). However, increasing citation impact is not the only benefit of self-archiving; work that is freely available for anyone to read should increase research access and impact, and allow those that fund research through their taxation access as well (Harnad, 2006, p. 73). There has been much discussion on the causes of this citation advantage. Kurtz et al. (2005), Davis and Fromerth (2006) and Moed (2006) are not convinced that simply making an article open access is sufficient cause for any increased citation counts. Rather, they suggest that authors may self-archive their better quality work, and because some articles are made available as preprints before publication, they have a longer period in which to attract citations. Metcalfe (2006, p. 549), however, thinks that, in solar physics at least, higher citation rates are not the result of authors archiving their higher quality papers, or necessarily that better authors more readily archive their work. What is evident, however, despite what might be the cause of any OA citation advantage, is that the evidence accumulated so far indicates that those authors who make their peer-reviewed work more visible by self-archiving their articles receive more citations than those who do not.