Bradford's law
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Bradford's law is a pattern first described by Samuel C. Bradford in 1934 that estimates the exponentially diminishing returns of extending a search for references in science journals. There are a number of related formulations of the principle.
In economics this pattern is called a Pareto distribution. As a practical example, suppose that a researcher has 5 core scientific journals for their subject. Suppose that in a month there are 12 articles of interest in those journals. Suppose further that in order to find another dozen articles of interest, the researcher would have to go to 10 journals. Then that researcher's Bradford multiplier bm is 2 (ie 10/5). For each new dozen articles, that researcher will need to look in bm times as many journals. After looking in 5, 10, 20, 40, ... journals, most researchers quickly realize that there is little point in looking further.
Different researchers have different numbers of core journals, and different Bradford multipliers. But the pattern holds quite well across many subjects, and may well be a general pattern for human interactions in social systems. Like Zipf's law, to which it is related, we do not have a good explanation for why it works. But knowing that it does is very useful for librarians. What it means is that for each specialty it is sufficient to identify the "core publications" for that field and only stock those. Very rarely will researchers need to go outside that set.
However its impact has been far greater than that. Armed with this idea and inspired by Vannevar Bush's famous article As We May Think, Eugene Garfield at the Institute for Scientific Information in the 1960s undertook the development of a comprehensive index of how scientific thinking propagates. The creation of his Science Citation Index (SCI) had the effect of making it easy to identify exactly which scientists did science that had an impact, and which journals that science appeared in. It also caused the discovery.which some did not expect, that a few journals like Nature and Science were core for all of hard science. The same pattern does not happen with the humanities or the social science - possibly because objective truth is so much harder to establish there, or because literature use in these fields is more diffuse, with less emphasis on journals.
The result of this is pressure on scientists to publish in the best journals, and pressure on universities to ensure access to that core set of journals.
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[edit] References
- Bradford, S.C. "Sources of Information on Specific Subjects". Engineering: An Illustrated Weekly Journal (London), 137, 1934 (26 January), pages 85-86.
- Reprinted as:
- Bradford, S.C. “Sources of information on specific subjects”. J. Information Science, 10:4, 1985 (October), pages 173 - 180.
- Bradford, S.C., "Sources of Information on Specific Subjects", in Lecture notes in computer science, No. 207: The Analysis of concurrent systems : Cambridge, September 12-16, 1983, edited by B.T. Denvir et. al. New York: Springer-Verlag, 1985, pages 173-180.
[edit] Related laws and distributions
Zipf's law, originally used for word frequencies Zipf-Mandelbrot law. Benford's law, originally used to explain apparently non-random sampling Pareto distribution, originally representing the distribution of wealth among individuals in a capitalist economic system.
Zeta distribution Power law the most general mathematical distribution
