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![]() Trends in Influential Articles and JournalsA publishing center's authorship of prominent S&E articles can be an indicator of the quality or influence of the research results it produces. Two citation measures are used to gauge quality and influence: (1) the frequency with which an article is cited and (2) the frequency of citation to the journal in which the article appears. Better and more influential articles tend to generate more citations.[12] Because articles in frequently cited journals[13] tend to be more widely noticed, these journals are able to attract better submissions and to publish better articles. These citation measures provide an indication of capability and competitiveness at the frontiers of research. Shares of highly cited articles are used to analyze trends because worldwide counts of highly cited articles fluctuate for reasons unrelated to influence (see sidebar "Methodology for Determining Influential Article Counts by Percentile"). Unless otherwise noted, the top 5% share of cited articles and journals is used as the measure of highly influential research. Results were similar when analyses were conducted using other percentile shares (see sidebar "Trends in Various Percentiles of Cited Articles and Journals"). United StatesThe U.S. share of the world's highly influential S&E articles slipped between 1992 and 1996 (appendix table 8). It then dropped more substantially, from 56% in 1996 to 50% in 2003 (figure 7 By field, the change in the U.S. share of highly influential articles was largely similar to the change in the U.S. share of total article output (figures 5 Whole-count trends in the U.S. share of the world's highly influential articles between 1996 and 2003 were similar to fractional-count trends: the U.S. lost share while the shares of the three other major S&E publishing centers increased. The U.S. whole-count share during this period fell from 62% to 58% (figure 8 The U.S. whole-count share declined in all fields between 1996 and 2003, but the size of the decline varied by field (figure 8 Between 1996 and 2003, the overall decline in the U.S. share of articles published in highly influential journals was similar to the decline in highly influential articles (figure 9 The percentage of total U.S. article output classified as highly cited is a somewhat different indicator of quality and influence. It indicates whether prominent articles are becoming more or less common in the output that the United States generates. This percentage remained steady between 1996 and 2003 and was higher than would be expected by chance (i.e., above 5%) (table 4 The EU-15, Japan, and the East Asia-4The EU-15's share of the world's highly influential articles rose slightly from 28% in 1996 to 31% in 2003 (
figure 7 Japan's share of the world's highly influential articles remained steady, rising slightly in all fields except the social sciences and psychology during the post-1996 period (figure 7 The East Asia-4's share of the world's highly influential articles more than quadrupled but remained very low overall, rising from less than 1% in 1996 to 2% in 2003 (figure 7 Among U.S., EU-15, and Japanese articles, the percentage classified as highly influential remained roughly constant between 1996 and 2003. In contrast, the percentage of East Asia-4 articles in this category doubled during this period (table 5
Footnotes
[12] Citations are not a straightforward measure of either quality or influence. Other factors affect what authors choose to cite; e.g., they are likely to cite their own previous articles and the work of colleagues, mentors, friends, or scientists in their own country. Different fields have different citation patterns. In addition, authors who are members of relatively large disciplinary or national communities are cited more frequently than those in smaller communities. [13] Journals are ranked by the average number of citations to articles published in each journal. Because the journal citation ranking is an average, articles appearing in highly cited journals may not necessarily be highly cited. [14] Citation counts are based on a 3-year period with a 2-year lag. In 2003, for example, a highly influential article is an article published between 1999 and 2001 that received more citations in 2003 than 95% of the articles published in these years. Because of the lag between publication and citation, the measure of highly influential articles begins with 1992, using data on articles cited in that year that were published between 1988 and 1990. [15] In analyses of the entire set of S&E articles, the number of articles in the database as a whole is used to calculate the top 5% considered to be highly influential. Because citation patterns vary from field to field, this method of determining the number of highly influential articles causes articles in some fields to be overrepresented and articles in other fields to be underrepresented. However, when citation counts are analyzed by field, articles are classified as highly influential if they are among the top 5% cited in their field, which partially controls for field differences in citation patterns. Thus, the same article may be classified as highly influential in some analyses and not highly influential in others.
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