Confirmation Bias and the Open Access Advantage: Some Methodological Suggestions for the Davis Citation Study

Harnad, Stevan (2008) Confirmation Bias and the Open Access Advantage: Some Methodological Suggestions for the Davis Citation Study s.n.


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: Davis (2008) analyzes citations from 2004-2007 in 11 biomedical journals. For 1,600 of the 11,000 articles (15%), their authors paid the publisher to make them Open Access (OA). The outcome, confirming previous studies (on both paid and unpaid OA), is a significant OA citation Advantage, but a small one (21%, 4% of it correlated with other article variables such as number of authors, references and pages). The author infers that the size of the OA advantage in this biomedical sample has been shrinking annually from 2004-2007, but the data suggest the opposite. In order to draw valid conclusions from these data, the following five further analyses are necessary: (1) The current analysis is based only on author-choice (paid) OA. Free OA self-archiving needs to be taken into account too, for the same journals and years, rather than being counted as non-OA, as in the current analysis. (2) The proportion of OA articles per journal per year needs to be reported and taken into account. (3) Estimates of journal and article quality and citability in the form of the Journal Impact Factor and the relation between the size of the OA Advantage and journal as well as article “citation-bracket” need to be taken into account. (4) The sample-size for the highest-impact, largest-sample journal analyzed, PNAS, is restricted and is excluded from some of the analyses. An analysis of the full PNAS dataset is needed, for the entire 2004-2007 period. (5) The analysis of the interaction between OA and time, 2004-2007, is based on retrospective data from a June 2008 total cumulative citation count. The analysis needs to be redone taking into account the dates of both the cited articles and the citing articles, otherwise article-age effects and any other real-time effects from 2004-2008 are confounded. Davis proposes that an author self-selection bias for providing OA to higher-quality articles (the Quality Bias, QB) is the primary cause of the observed OA Advantage, but this study does not test or show anything at all about the causal role of QB (or of any of the other potential causal factors, such as Accessibility Advantage, AA, Competitive Advantage, CA, Download Advantage, DA, Early Advantage, EA, and Quality Advantage, QA). The author also suggests that paid OA is not worth the cost, per extra citation. This is probably true, but with OA self-archiving, both the OA and the extra citations are free.

Item Type: Monograph (Project Report)
Additional Information: Commentary On: Davis, P.M. (2008) Author-choice open access publishing in the biological and medical literature: a citation analysis. Journal of the American Society for Information Science and Technology (JASIST) (in press)
Related URLs:
Keywords: citation analysis, open access, scientometrics, multiple regression, JASIST, Davis, Kurtz, research impact
Organisations: Web & Internet Science
ePrint ID: 266600
Date :
Date Event
26 August 2008Accepted/In Press
Date Deposited: 26 Aug 2008 17:46
Last Modified: 17 Apr 2017 19:01
Further Information:Google Scholar

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