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Self-Selected or Mandated, Open Access Increases Citation Impact for Higher Quality Research

Figure 2

Log Citation Ratios Comparing the Yearly OA Impact Advantage for Self-Selected vs Mandatory OA 2002–2006.

O = OA article (Open Access); Ø = non-OA article (non-Open Access); M = Mandated OA; S = Self-Selected OA. Averages across the sample of four institutions with self-archiving mandates confirm the significantly higher citation counts for OA articles (symbolized here as “O”) compared to matched control non-OA articles (symbolized here as “Ø”) published in the same journal and year. They are compared as O/Ø log ratios in the seven comparisons. (The first comparison, O/Ø, for example, is the arithmetic mean of all the (log) ratios O/Ø for each of the 5 years.) OA articles are more highly cited irrespective of whether the OA is Self-Selected (S) or Mandated (M). The O/Ø Advantage is present for mandated OA (OM/ØS) and is of about the same magnitude irrespective of whether we compare the S ratios with the M ratios for the entire control sample (OS/Ø vs OM/Ø) or just compare S alone with M alone (OS/ØS vs OM/ØM). (The larger values for year 2006 are almost certainly due to the fact that 2006 was still too near to have stabilized at the time this analysis was conducted (2008–9); the analysis has since been extended for years 2006–2008, thereby stabilizing the data for 2006 and 2007, and yields the same results, always with the exception of the most recent year, which was 2008 in the most recent analysis.)

Figure 2

doi: https://doi.org/10.1371/journal.pone.0013636.g002