Citations: Citations, generally at the end of each article, provide researchers with the list of the prior research relied on for the article. Citations of S&E publications by other S&E publications provide an indication of the impact of publications and of the flow of knowledge or linkage between sectors or geographic locations.

Coauthorship: Coauthorship refers to cases in which more than one author is listed on a publication. Data on coauthorship can be used to measure collaboration across regions, countries, economies, and institutional sectors. Publication counts of coauthorship use whole counting, so each region, country, or economy contributing to the article receives credit for that article. An article is considered to contain an international coauthorship when institutional addresses for its authors are located in two or more different regions, countries, or economies. Table SPBS-36 shows international coauthorship from 2003 to 2022.

European Union (EU-27): The EU comprises 27 member nations: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, and Sweden. Bulgaria and Romania joined the EU in 2007, and Croatia joined in 2013—these nations are included in the EU grouping for all years analyzed in this report. In 2020, the United Kingdom left the EU, and data covering the United Kingdom are excluded from the EU-27 in the text of the report but are available in the supplemental tables as “EU-27 and United Kingdom.”

Fractional counting: A method of counting S&E publications in which credit for coauthored publications is divided among the collaborating institutions or regions, countries, or economies based on the proportion of their participating authors. Fractional counting allocates the publication count based on the proportion of the coauthors named on the article with institutional addresses from each region, country, or economy. Fractional counting enables the counts to sum up to the number of total articles. For example, if a publication were authored by two researchers from the University of Oslo, one from University College London, and one from the University of Washington, half of the publication would be attributed to Norway, and a quarter each to the United Kingdom and the United States when the fractions are calculated at the level of researchers. For this report, fractions were calculated at the level of researchers. If an author provides multiple institutions, and those institutions are in different regions, countries, or economies, then each region, country, or economy receives an appropriate fraction of the count.

Highly cited article (HCA): An HCA ratio provides an indication of scientific impact (Waltman, van Eck, and Wouters 2013). The HCA ratio for a region, country, or economy is calculated as the share of all articles published in a given year by authors with institutional addresses within that region, country, or economy that fall within the top 1% by citation count of all articles published that year, measured for each research field. The HCA ratio is indexed to 1.00, so a region, country, or economy whose authors produce highly cited articles at the expected (i.e., global average) rate has an HCA ratio of 1.00—that is, 1% of the region’s, country’s, or economy’s articles are among the top 1% of the world’s highly cited articles. A region, country, or economy with an HCA ratio greater than 1.00 is producing a disproportionately high level of articles with exceptional scientific impact, whereas a region, country, or economy whose authors produce relatively fewer influential articles will have an HCA ratio below 1.00.

International collaboration index (ICI): The ICI helps identify the propensity of collaboration between two regions, countries, or economies. The ICI is calculated as follows: Icxy = (Cxy / Cx) / (Cy / Cw), where Icxy is the index of collaboration between country x and country y, Cxy is the number of publications coauthored between country x and country y, Cx is the total number of international coauthorships by country x, Cy is the total number of international coauthorships by country y, and Cw is the total number of international coauthorships in the database. An index greater than 1.0 means that a country-country pair has a stronger-than-expected tendency to collaborate; an index less than 1.0 indicates a weaker-than-expected tendency to collaborate (Table SPBS-38).

Open access (OA): OA refers to peer-reviewed publications that are accessible online to any reader without requiring a journal subscription or other fees from readers (Piwowar et al. 2018). Several commonly defined types of OA have been adopted for the purposes of this analysis. Gold OA denotes articles published in journals that are entirely OA as a matter of journal policy. Hybrid OA refers to articles appearing in closed-access journals where the authors have paid a fee to make the article OA. Bronze OA denotes articles in closed-access journals that become OA after an embargo period of closed access or articles that appear available as OA despite lacking the license information to guarantee OA in the long term. Green OA denotes articles that are self-archived by authors in OA repositories, which are often maintained and administered by universities or other institutions.

Relative citation (RC): The RC is a normalization of the relative scientific impact of publications produced by a given region, country, or economy that takes into consideration variations in citation behavior between fields and years of publication. For a publication in a given scientific field and publication year, the citation count is divided by the average count of all publications in the relevant field and publication year.

Relative citation index (RCI): The RCI normalizes cross-national citation data for variations in relative size of publication output. It is computed by dividing the share of the citing region’s, country’s, or economy’s outgoing citations going to the cited region, country, or economy, then dividing this number by the share of publications attributed to the cited region, country, or economy.

Whole counting: This measure (also called full or integer counting) assigns one count to each region, country, or economy or institutional sector involved in coauthoring the article, irrespective of its proportionate involvement in authorship. Although fractional counting aims to assess the proportionate contributions of regions, countries, or economies or sectors, whole counting aims to assess the participation of regions, countries, or economies or sectors. One result of this difference is that the sum of articles from regions, countries, or economies or institutional sectors will exceed the total number of articles when whole counting is used. For the United States in 2022, there were 458,000 publications in the Scopus database as measured on a fractional-count basis and 608,000 as measured on a whole-count basis (Table SPBS-2 and Table SPBS-17). In the full-counting method, each publication is counted once for each entity listed in the address field. For example, if a publication were authored by two researchers from the University of Oslo, one from University College London, and one from the University of Washington, the publication would be counted once for Norway, once for the United Kingdom, and once for the United States. When it comes to aggregating groups of institutions (e.g., research consortia) or groups of countries (e.g., the EU-27), double counting is avoided. This means that if authors from Croatia and France co-published an article, this publication would be credited only once when counting publications for the EU-27, although each country had been credited with one publication count.

AI: artificial intelligence

APC: article processing charge

EU-27: European Union

HCA: highly cited article

ICI: international collaboration index

NCSES: National Center for Science and Engineering Statistics

NSB: National Science Board

OA: open access

R&D: research and development

RCI: relative citation index

S&E: science and engineering

TOD: Taxonomy of Disciplines