The impact of general and internal medicine journals publishing in 1959.

*Thomson ISI Journal Impact Factor, as derived from the 2008 Journal Citation Reports edition. It is calculated by dividing the total number of citations received in 2008 by items published in 2006 or 2007 by the number of original articles and reviews published in 2006 and 2007. Note that the nominator includes citations to all items published by a journal regardless of whether this is an original article, review or other type of item (e.g. editorial, essay, etc), while the denominator includes only original articles (articles and proceedings papers, a category that did not exist in 1959) and reviews. Moreover, the journal impact factor considers papers published during two years and the citations that they received in a single year (one or two years after their publication year, respectively). Therefore, the definition is slightly different from the 2-year citation impact metric that we used for papers published in 1959. The last column that shows the 2-year citation impact per paper for papers published in 2007 (citations to papers or reviews published in 2007 during 2008 and 2009 divided by the number of papers or reviews published in 2007) is conceptually identical to the respective metric for papers published in 1959. The Thomson ISI Journal Impact Factor was almost perfectly correlated with the 2-year impact of papers published in 2007 (r = 0.993, pJIF: journal impact factor; NP: not publishing currently; NI: not indexed in ISI Web of Science currently.