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The data above, on the top 20 European nations in the field of physics by citation impact, were extracted from the Essential Science Indicators database of Thomson Reuters. This database, currently covering the period January 2001 through February 2011, surveys only articles (original research reports and review articles) in journals indexed by Thomson Reuters.

Articles are assigned to a field based on the journals in which they were published and the Thomson Reuters journal-to-field scheme. Papers published in multidisciplinary journals such as Nature and Science are individually assigned to their appropriate fields. Both articles tabulated and citation counts to those articles are for the period indicated.

Here our ranking in physics is by citations per paper to reveal weighted influence. For articles with multiple authors from different nations, each nation receives full, not fractional, publication and citation credit. Essential Science Indicators lists nations ranked in the top 50 per cent for a field over a given period, based on total citations. In physics, 89 nations are listed, meaning 178 were surveyed. Thirty-two nations earned 50,000 or more citations during the period. The world average in citation impact for the field was 8.44, so 16 of the 20 nations above surpassed this mark. Also appearing is the world rank by impact for each of these European nations. As can be seen, the top nations in impact in physics worldwide are almost exclusively European, with the exception of the United States, at fourth in the world, which posted a citations-per-paper score of 13.64.

For more information on Thomson Reuters Essential Science Indicators, see .