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Data provided by Thomson Reuters from its Essential Science indicators, January 2000-April 2010

The data above were extracted from the Essential Science Indicators database of Thomson Reuters. This database, currently covering the period January 2000 to April 2010, surveys only journal articles (original research reports and review articles) indexed by Thomson Reuters. Articles are assigned to a category based on the journals in which they were published and the Thomson Reuters journal-to-category field-definition scheme. Both articles tabulated and citation counts to those articles are for the period indicated. Naturally, institutions publishing large numbers of papers have a greater likelihood of collecting more citations than those publishing fewer papers. This ranking is by citations per paper (impact) among those institutions that have published 500 or more papers in microbiology during the period. For papers with multiple institutional addresses, each institution receives full, not fractional, citation credit. Essential Science Indicators lists institutions ranked in the top 1 percent for a field over a given period, based on total citations. For the current version, 339 institutions are listed in the field of microbiology, meaning that a total of 33,900 institutions were surveyed to obtain these results. Of the 339, 85 institutions published 500 or more papers. The ranking by citations per paper (impact) seeks to reveal ¡°heavy hitters¡± based on per paper influence, not mere output, US institutions account for 18 of the top 20. For more information, see .