Citations to the work of others in the literature are a broad indicator of the usefulness of this work in ongoing research. Citations to nondomestic articles can indicate the existence of useful work being done elsewhere.
Citations in U.S. articles (henceforth, U.S. citations) to the domestic literature dropped steadily since 1992 from 69% to 60% in 2007, attesting to the growth of relevant work elsewhere. Figure
Most U.S. citations to the nondomestic literature referenced EU publications. In 2007, 23% of total U.S. citations were to EU work, up from about 18% in 1992 but flat in recent years. Over the same period, the Japanese share gradually declined. Slowly rising citation shares to work done in the Asia-8 group remained at a low level, partly because of the overall low level of their publications output, but probably also because of language, cultural barriers, and research quality.
EU citation patterns have undergone similar changes, with citations to the U.S. literature dropping from 36% to 28% over the 1992–2007 period. Total citations to Asian articles increased modestly from 5% to 8%, whereas citations to the rest of the world increased from 13% to 18%.
Major changes are evident in the Asia-10 group, whose internal citations increased from 37% to 41% of the Asia-10 total over the 1992–2007 period. Within this group, Japan's share dropped steeply from 31% to 17%, whereas China's share increased from 2% to 12% and the Asia-8's share increased from 5% to 12%. The EU share slowly increased, whereas the U.S. share declined from 36% to 27% (figure
The sheer number of citations by Chinese authors is rising steeply, but in a relative sense, Chinese authors are increasingly citing domestic articles and those by researchers in the Asia-8 group but less frequently the work of U.S. scientists. Thus, although the number of citations to U.S. articles increased from about 6,000 in 1992 to approximately 82,000 in 2007, the U.S. share contracted from 36% to 25%. Japan's share of citations in the Chinese literature has basically remained unchanged since the early 1990s; the same holds for the EU (figure
Even as global production and citation patterns have shifted, the relative quality distribution of worldwide articles, as measured by citations, has changed little. In 2007, the United States had consistently higher proportions of its articles in the most highly cited categories than the EU or the Asia-10 (figure