Science, 251:1410-1411, 1991
David A. Pendlebury
Letters to the Editor
Science, Citation, and Funding
Hamilton's two articles about the percentage of journal literature that remains uncited within 5 years of publication require comment and further explanation. The figures reported by Hamilton -- 47.4% uncited for the sciences, 74.7% for the social sciences, and 98.0% for the arts and humanities -- are indeed correct. However, as Maxine Singer was quoted as saying in Hamilton's first article, it is necessary to know what's in the numbers before interpreting them.
These statistics represent every type of article that appears in journals indexed by the Institute for Scientific Information (ISI) in its Science Citation Index, Social Sciences Citation Index, and Arts & Humanities Citation Index. The journals' ISI indexes contain not only articles, reviews, and notes, but also meeting abstracts, editorials, obituaries, letters like this one, and other marginalia, which one might expect to be largely un-cited. In 1984, the year of the data quoted by Hamilton, about 27% of the items indexed in the Science Citation Index were such marginalia. The comparable figures for the social sciences and arts and humanities were 48% and 69%, respectively.
If one analyzes the data more narrowly and examines the extent of uncited articles alone (this information was not yet available when Hamilton wrote his articles), the figures shrink, some more than others: 22.4% of 1984 science articles remained uncited by the end of 1988, as did 48.0% of social sciences articles and 93.1% of articles in arts and humanities journals. It ought to be pointed out that the book represents a considerably more important vehicle of communication in the social sciences and humanities than in the sciences. The figures given above reflect only the journal literature of the social sciences and arts and humanities.
The figures originally quoted by Hamilton seem to have been interpreted by many readers as some sort of measure of the health of U.S. science. The numbers, however, reflect a lack of citation of papers by authors the world over-not only those by U.S. researchers. This point was raised in Hamilton's first article.
If one restricts the analysis even further and examines the extent of uncited articles by U.S. authors alone, the numbers are even less "worrisome." Only 14.7% of 1984 science articles by U.S. authors were left un-cited by the end of 1988. We estimate the share of uncited 1984 articles by non-U.S. scientists to be about 28%. (Comparable figures for social sciences and arts and humanities articles by U.S. authors are not yet available.)
A certain level of "uncitedness" in the journal literature is probably more an expression of the process of knowledge creation and dissemination than any sort of measure of performance. A trend toward more or less "uncitedness," however, might be meaningful. For the 1980s, we see no such trend in the scientific literature: the numbers are essentially flat, both for the United States alone and for the world. In the social sciences, however, we do detect a decrease in uncited papers -- from 49.7% for 1981 articles to 45.3% for 1985 articles. In the arts and humanities, the figure of 93% uuncited is fairly steady from 1981 through 1985.
This, we hope, serves to illustrate the great range of statistics one can derive depending upon what "cut" is made from the ISI databases. For example, articles published in the highest impact journals like Science are almost never left uncited.
We will be generating, over the coming months, article-only statistics, both U.S. and worldwide, for subdisciplines in the sciences, social sciences, and humanities, corresponding to the overall database statistics referred to by Hamilton in his second article. We have not yet produced a report on these statistics, but in light of the great interest in the numbers, we will now do so.
We hope this information clarifies the record and will end further misunderstanding or politicalization of these statistics.
David A. Pendlebury
Institute for Scientific Information
3501 Market Street
Philadelphia, PA 19104
Articles by David Hamilton:
David Hamilton, "Publishing by -- and for? -- the Numbers"
Science, 250:1331-2, 1990
David Hamilton, "Research Papers: Who's Uncited Now?"
Science, 251:25, 1991