Online-to-print publication lags inflate impact factors.

<p>(A) Schematic representation of the lag-corrected impact factor index. The 2010 impact factor (<i>top</i>) is calculated by considering the number of citations in 2010 to articles officially published (i.e. in print) in 2008 and 2009, divided by the number of articles officially published in 2008 and 2009. The lag-corrected 2010 impact factor (<i>bottom</i>) considers the number of citations in 2010 to articles that were published online in 2008 and 2009, divided by the number of articles published online in 2008 and 2009. (B) Actual and lag-corrected impact factors for the same 31 journals as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053374#pone-0053374-g001" target="_blank">Figure 1B</a>. Lag-corrected impact factor is smaller than the actual one for all journals (p<10⁻⁵, paired t-test). (C) Scatter plot showing a strong correlation between the difference between actual and corrected impact factors (in %) and the duration of the publication lag (r = 0.90, p<10⁻¹¹).