Impact of Published Research
The global scientific publication enterprise cannot simply be categorized by its volume of production, the degree of article use matters as well. This is measured by the patterns and flows of citations. Data from citations provides a window into the impact of specific articles and authors, as well as the return on a country’s scientific investment (Narin and Hamilton 1996). Publications are also used in patenting technologies, which will be covered in the forthcoming Indicators 2020 report “Invention, Knowledge Transfer, and Innovation.”
Citation data provide indications of scientific impact or influence by counting how frequently other journal articles or conference papers reference an article. Publications with more citations are said to have more impact on a particular scientific discipline (Waltman, Van Eck, and Wouters 2013). A small subset within the count of cited articles are categorized as highly cited articles (HCA), or the publications most frequently cited in other researchers' articles and conference papers. This report presents data on the top 1% of most-cited publications.The index of a country’s number of highly cited articles relative to the world’s highly cited articles creates a comparable cross-country measure.
The United States contributed nearly twice the expected volume of HCA in 2016 (HCA score of 1.9) (Figure 5a-9). China's HCA score is just above its expected share (HCA score of 1.1). Not all major article-producing countries were above the world average HCA—Japan and India each had below their expected level of articles in the top 1% in 2016 (HCA scores of 0.9 and 0.7, respectively) (Figure 5a-9). This report provides data for 2016 because HCA scores require the passage of time following publication for other researchers to read, analyze, and cite the articles (Wang 2012).
S&E publication output in the top 1% of cited publications, by selected country or economy: 1996–2016
EU = European Union.
Articles are classified by their year of publication and are assigned to a region, country, or economy on the basis of the institutional address(es) of the author(s) listed in the article. Citation data are based on all citations made to articles in their publication year and all following years and are normalized by subfield and publication year to allow for comparisons across subfields and over time, resulting in the world-level standing at 1 for each subfield and year. A minimum 2-year citation window is needed for a relative citation (RC) score to be computed. This results in scores regarding highly cited articles not being computed after 2016 because the citation window for more recent years is not yet complete. The share of articles in the top 1% is computed as follows: Sx = HCPx/Px, where Sx is the share of output from country x in the top 1% most-cited articles; HCPx is the number of articles from country x that are among the top 1% of most-cited articles (using full counting, with the exception of papers at the limit of the top 1%, which are fractioned so the world average can stand at 1%); and Px is the total number of papers from country x with an RC score, which excludes articles released after 2016 and unclassified publications. The world average stands at 1.00 for each year. See Table S5a-35 for source data. See Table S5a-1 for countries included in the EU.
National Center for Science and Engineering Statistics, National Science Foundation; Science-Metrix; Elsevier, Scopus abstract and citation database, accessed June 2019.
Science and Engineering Indicators
In addition to cross-country comparisons, the HCA score provides an opportunity to understand changes in a country’s representation within the most highly cited articles. From 2006 to 2016, the impact of Chinese researchers grew faster than the impact of researchers in the United States and other countries (Conte et al. 2017; Xie and Freeman 2018). The HCA score of the United States increased slightly from 1.8 in 2006 to 1.9 in 2016 (Figure 5a-9). Over the same decade, the share of Chinese articles among the top 1% most-cited articles doubled (with HCA scores of 0.5 in 2006 and 1.1 in 2016) (Figure 5a-9). In 2006, publications from India had slightly more impact compared to China, although India's HCA score has remained relatively flat fluctuating around 0.7 over the 2006 to 2016 period (Figure 5a-9). HCA scores for Japan have increased from 0.6 in 2006 to 0.9 in 2016 (Figure 5a-9). The HCA score for China roughly equaled Japan’s score in 2011; however, China's percentage of articles in the top 1% has surpassed Japan's since 2012 (Figure 5a-9).
The EU’s HCA score increased from 1.1 in 2006 to 1.3 in 2016, driven by the growth of highly cited research from several member countries, such as the UK (which increased from 1.7 in 2006 to 2.4 in 2016), Germany (which increased from 1.3 in 2006 to 1.8 in 2016), and France (which increased from 1.3 in 2006 to 1.7 in 2016) (Table S5a-35).