[Does open access publishing increase the impact of scientific articles? An empirical study in the field of intensive care medicine].
OBJECTIVE
Some studies suggest that open access articles are more often cited than non-open access articles. However, the relationship between open access and citations count in a discipline such as intensive care medicine has not been studied to date. The present article analyzes the effect of open access publishing of scientific articles in intensive care medicine journals in terms of citations count.


METHODS
We evaluated a total of 161 articles (76% being non-open access articles) published in Intensive Care Medicine in the year 2008. Citation data were compared between the two groups up until April 30, 2011. Potentially confounding variables for citation counts were adjusted for in a linear multiple regression model.


RESULTS
The median number (interquartile range) of citations of non-open access articles was 8 (4-12) versus 9 (6-18) in the case of open access articles (p=0.084). In the highest citation range (>8), the citation count was 13 (10-16) and 18 (13-21) (p=0.008), respectively. The mean follow-up was 37.5 ± 3 months in both groups. In the 30-35 months after publication, the average number (mean ± standard deviation) of citations per article per month of non-open access articles was 0.28 ± 0.6 versus 0.38 ± 0.7 in the case of open access articles (p=0.043). Independent factors for citation advantage were the Hirsch index of the first signing author (β=0.207; p=0.015) and open access status (β=3.618; p=0.006).


CONCLUSIONS
Open access publishing and the Hirsch index of the first signing author increase the impact of scientific articles. The open access advantage is greater for the more highly cited articles, and appears in the 30-35 months after publication.
Servicio de Medicina Intensiva, Hospital Universitario Son Espases, Palma de Mallorca, España. rierasagrera@gmail.com
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D022126:Access to Information; D003422:Critical Care; D055811:Journal Impact Factor; D010506:Periodicals as Topic / Q000706:statistics & numerical data*; D011643:Publishing / Q000706:statistics & numerical data*