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Institution	Papers	Citations	Citations per paper
1 Institute for Genomic Research, US	189	12,783	67.63
2 Wellcome Trust Sanger Institute, UK	156	10,203	65.40
3 Princeton University, US	292	10,544	36.11
4 Rockefeller University, US	437	15,448	35.35
5 Columbia University, US	379	12,865	33.94
6 Washington University, US	770	25,048	32.53
7 Harvard University, US	2,025	62,373	30.80
8 Scripps Research Institute, US	640	18,914	29.55
9 University of Iowa, US	683	19,987	29.26
10 Stanford University, US	899	25,748	28.64
11 Technical University of Denmark, Denmark	478	13,558	28.36
12 Northwestern University, US	544	15,248	28.03
13 Max Planck Society, Germany	1,206	33,331	.64
14 University of Pennsylvania, US	921	25,415	.60
15 University of Oxford, UK	1,035	28,368	.41
16 University of California San Francisco, US	675	18,434	.31
17 Duke University, US	553	15,044	.20
18 Natl Inst Allergy & Infectious Diseases, US	1,505	40,939	.20
19 University of Washington, US	1,198	32,513	.14
20 University of California Berkeley, US	611	16,523	.04

The data above were extracted from the Essential Science Indicators database of Thomson Reuters. This database, currently covering the period January 1998 through June 2008, 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 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 collected 10,000 or more citations in microbiology. For papers with multiple institutional addresses, each institution receives full, not fractional, citation credit. Essential Science Indicators lists institutions ranked in the top 1 per cent for a field over a given period, based on total citations. For the current version, 298 institutions are listed in the field of immunology, meaning that a total of 29,800 institutions were reviewed to obtain these results. Of the 298, 75 institutions collected 10,000 or more citations. The ranking by citations per paper (impact) seeks to reveal ¡°heavy hitters¡± based on per paper influence, not mere output. For more information on Thomson Reuters¡¯ Essential Science Indicators, see .