1. 1 More information on the selection of documents for analysis can be found in the Technical Appendix for this report.

  2. 2 Data can also be examined for institutional collaboration (NSB Indicators 2018: Coauthorship and Collaboration in S&E Literature).

  3. 3 Publication output only includes those indexed in the Scopus database. The publication output discussion uses fractional counting, which credits coauthored publications according to the collaborating institutions or countries, based on the proportion of their participating authors. Country assignments refer to the institutional address of authors, with partial credit given for each international coauthorship. As part of our data analysis, we employ filters on the raw Scopus S&E publication data to remove publications with questionable quality, which appear in what are sometimes called “predatory” journals (NSB Indicators 2018: Bibliometric Data Filters sidebar).

  4. 4 This report uses the World Bank’s country income classifications issued on July 1, 2018. The World Bank updates the classifications each year on July 1. The World Bank income classifications are assigned using the gross national income per capita as measured in current U.S. dollars. This report uses the rankings. More information is available at

  5. 5 Year-to-year comparisons across Indicators reports are not possible because the bibliometric database constantly updates as new articles enter the database and additional information becomes available. The publication output trends and year-to-year comparisons are valid within all the 2020 Indicators reports because they all rely upon the June 2019 Scopus database download.

  6. 6 The trends are consistent whether using fractional counting as in Figure 5a-3 and Table 5a-1 or whole counting as in Table S5a-2. There is a slight difference between the United States and China when looking at the whole counting total production numbers. Using whole counting for 2018, the United States had 548,847 articles while China had 584,407. A whole counting measure allocates one full count to each country with an author contributing to the paper, rather than fractional counting where each country only receives a fraction. For example, if an article had four authors with two from the United States, one from China, and one from Brazil, the fractional scores would be 2/4 for the United States, 1/4 for China, and 1/4 for Brazil. The difference between whole and fractional counting indicates that the United States has more authors working with Chinese authors than China has working with U.S. authors.

  7. 7 The Group of Seven (G7) is an international intergovernmental economic organization consisting of the seven largest International Monetary Fund members: Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States.

  8. 8 A grouping acronym referring to the countries of Brazil, Russia, India, and China.

  9. 9 The worldwide international collaboration rates should not be used as benchmarks against which to compare the share of international co-publications of individual countries. Due to the multi-lateral nature of co-publications, the world's share based on full counting of co-publications and publications is not directly comparable to the country scores. Individual country scores also use whole counting where each country, with an institutional address on the paper, receives one point. Therefore the basis count for individual countries will be larger than the number of papers that have authors with institutional addresses from 2 or more countries, which is the basis for the worldwide collaboration computation.

  10. 10 Figure 5a-7 uses whole counting: each collaborating country or economy is credited with one count. The United States has a larger number of articles on a whole-count basis because the United States is more collaborative than China. Accurate cross-country comparisons for article production uses fractional counting as shown in Figure 5a-3.

  11. 11 The United States serves in a leadership position in international collaboration as determined by the number of times that an author from a U.S. institution is listed first among an article’s authors. See Chinchilla-Rodríguez Z, Sugimoto CR, Larivière V. 2019. Follow the Leader: On the Relationship between Leadership and Scholarly Impact in International Collaborations. PLOS ONE 14(6):e0218309. Available at Accessed 18 September 2019.

  12. 12 The difference between 2018 and 1996 index values are rounded to show trends; some index values are slightly negative due to year-to-year fluctuations. A 22-year time span is used because international collaboration is a slow-moving trend.

  13. 13 Table S5a-35 presents data on the top 1%, 5%, and 10% HCA.

  14. 14 The share of S&E articles in the top 1% of cited articles is computed by field because different fields of science have different rates of citation.