n numerous occasions, this publication has assessed the citation impact of research produced by various nations, typically by enumerating total citations or calculating average citations per paper. This time, however, Science Watch takes a slightly different tack and asks a particular question: what percentage of a nation’s papers rank among the top 1% most cited, both overall and in a selection of specialty fields?

To examine this matter, Science Watch turned to Thomson Scientific’s Essential Science Indicators^SM (ESI) web-based evaluation tool.¹ Along with its store of publication and citation statistics covering a moving ten-year window (with successive bimonthly updates), ESI offers assorted baseline statistics, including citation percentiles for each of the 22 main fields tracked by the database. These figures indicate the citation thresholds necessary for a paper, published in a given field and a given year, to rank in six separate percentiles—specifically, among the top 50%, 20%, 10%, 1%, 0.1%, and 0.01% most-cited papers. These thresholds are displayed for each year within the ten years of ESI coverage, and are also shown in a cumulative "all years" figure, which, as of this writing, corresponds to ESI’s current window, covering papers published and cited between 1996 and 2006. For this survey, Science Watch employed this "all years" formulation and the top 1% percentile.

The citation thresholds in the respective percentiles vary considerably by field, reflecting different citation patterns in different disciplines. For example, the "all years" citation figure for a paper to rank among the top 1% in Clinical Medicine is 110; in Chemistry, by contrast, a total of 77 citations meets the 1% threshold, while 35 or more citations in Engineering will attain the top 1% mark.

The table to the right includes 13 selected countries (arranged in alphabetical order), showing each nation’s total number of papers for the past decade, followed by its number of papers that rank among the top 1% most cited—that is, the number of papers that reach the top 1% citation percentile according to the "all fields and "all years" thresholds in ESI. The next column shows this actual percentage (e.g., for Australia, 2,804 of the nation’s 248,189 papers, or 1.13%, reach the top 1% most-cited threshold based on papers published and cited during the last ten years).

The right-hand column displays each nation’s percentage of top-cited papers in slightly different terms, comparing it against an "expected" baseline of 1% (or, in the actual percent-change calculation, against 1.00). Hence, Australia’s 1.13% is also rendered here as 13% above the expected rate of papers within the top 1%.

In the same table, the United States demonstrates the highest percentage of its total papers making the top 1% threshold, with a mark 87% above the expected rate. England displays the next-highest rate, at 53% above, with Canada not far behind at 34% above the baseline. Among nations in which English is not the predominant language, Germany fares best, with its percentage of top-cited papers at 27% above the expected rate. And of the Asian countries listed here, Japan displays the highest rate of top papers compared to its neighbors, with its percentage of 0.72% being 28% below the baseline.

The tables below reflect a similar calculation, showing each nation’s comparative percentage (against the expected rate) in ten main fields of science, divided into life-sciences and physical-sciences categories. In Clinical Medicine, for example, 745 of Australia’s 53,650 Thomson-indexed papers in this field, or 1.39%, achieved the top 1% threshold, with the figure rendered here as 39% above the expected threshold. Canada’s figure of 1,625 out of its 80,138 Clinical Medicine papers, meanwhile, results in a rate 103% above the baseline.

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