Introduction

Wikipedia, one of the most visited websites in the world,1 has become a destination for information of all kinds, including information about science (Heilman & West, 2015; Laurent & Vickers, 2009; Okoli, Mehdi, Mesgari, Nielsen, & Lanamäki, 2014; Spoerri, 2007). Given that so many people rely on Wikipedia for scientific information, it is important to ask whether Wikipedia's coverage of science is a balanced, high quality representation of the knowledge within the academic literature. One approach to asking this question involves looking at references used in Wikipedia articles. Wikipedia requires all claims to be substantiated by reliable references,2 but what, in practice, are “reliable references?”

An intuitive approach is to compare the sources Wikipedia editors use to the sources scientists value most. In particular, within the scientific literature, a journal's status is often associated, albeit problematically (Seglen, 1997), with its impact factor. If status within the academic literature is taken as a “gold standard,” Wikipedia's failure to cite high impact journals of certain fields would constitute a failure of coverage (Samoilenko & Yasseri, 2014), whereas a high correspondence between journals' impact factors and citations in Wikipedia would indicate that Wikipedia does indeed use reputable sources (Evans & Krauthammer, 2011; Nielsen, 2007; Shuai, Jiang, Liu, & Bollen, 2013).

Yet high impact journals often require expensive subscriptions (Björk & Solomon, 2012). The costs are, in fact, so prohibitive that even Harvard University has urged its faculty to “resign from publications that keep articles behind paywalls” because the library “can no longer afford the price hikes imposed by many large journal publishers” (Sample, 2012). Consequently, many within the scientific community advocate journals that provide free access to research ‐ “open access” (OA) journals. (Van Noorden, 2013). A lively debate has arisen on the impact of OA on the scientific literature, with some studies showing a citation advantage to publishing in OA versus paywall journals (Eysenbach, 2006a, 2006b; Gargouri et al., 2010; “The Open Access Citation Advantage Service”) whereas others find none (Davis, 2011; Davis, Lewenstein, Simon, Booth, & Connolly, 2008; Gaulé & Maystre, 2011; Moed, 2007).

Regardless of their impact on the scientific literature, OA journals may have a tremendous impact on the diffusion of scientific knowledge beyond this literature. To date, this potential of OA policies has been a matter chiefly of speculation (Heilman & West, 2015; Trench, 2008). Previous research has found that OA articles are downloaded from publishers' websites more often and by more people than closed access articles (Davis, 2010, 2011), but it is currently unclear by whom, and to what extent open access affects the use of science by the general public (Davis & Walters, 2011). We hypothesize that Wikipedia, with more than 8.5 million page views per hour,3 is a new but crucial pathway through which the public consumes science and this diffusion of science may relate to its accessibility in two ways. By referencing findings from paywall journals that may be prohibitively expensive, Wikipedia distills and diffuses these findings to the general public. On the other hand, Wikipedia editors may be unable to access expensive paywall journals,4 and consequently reference the easily accessible articles instead. For example, Luyt and Tan's (2010) study found accessibility to drive the selection of references in a sample of Wikipedia's history articles. In this case Wikipedia “amplifies” open access science by broadcasting its (already freely accessible) findings to millions. This “amplifier” effect may thus constitute one of the chief effects of open access.