Bradford's law
Encyclopedia
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. One formulation is that if journals in a field are sorted by number of articles into three groups, each with about one-third of all articles, then the number of journals in each group will be proportional to 1:n:n². There are a number of related formulations of the principle.
In many disciplines this pattern is called a Pareto distribution. As a practical example, suppose that a researcher has five core scientific journal
s for his or her 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 an additional 10 journals. Then that researcher's Bradford multiplier bm is 2 (i.e. 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, etc. 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 developed a comprehensive index of how scientific thinking propagates. 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, such as Nature
and Science
, were core for all of hard science. The same pattern does not happen with the humanities or the social sciences.
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. On the other hand, the set of "core journals" may vary more or less strongly with the individual researchers, and even more strongly along schools-of-thought divides. There is also a danger of over-representing majority views if journals are selected in this fashion.
Bradford's law is also known as Bradford's law of scattering and as the Bradford distribution. This law or distribution in bibliometrics can be applied to the World Wide Web
.
They found that the literature of Bradford's law (including Bradford's own papers) are unclear in relation to which kind of scattering is actually being measured.
Diminishing returns
In economics, diminishing returns is the decrease in the marginal output of a production process as the amount of a single factor of production is increased, while the amounts of all other factors of production stay constant.The law of diminishing returns In economics, diminishing returns (also...
of extending a search for references in science journals. One formulation is that if journals in a field are sorted by number of articles into three groups, each with about one-third of all articles, then the number of journals in each group will be proportional to 1:n:n². There are a number of related formulations of the principle.
In many disciplines this pattern is called a Pareto distribution. As a practical example, suppose that a researcher has five core scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
s for his or her 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 an additional 10 journals. Then that researcher's Bradford multiplier bm is 2 (i.e. 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, etc. 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
Vannevar Bush
Vannevar Bush was an American engineer and science administrator known for his work on analog computing, his political role in the development of the atomic bomb as a primary organizer of the Manhattan Project, the founding of Raytheon, and the idea of the memex, an adjustable microfilm viewer...
's famous article As We May Think
As We May Think
As We May Think is an essay by Vannevar Bush, first published in The Atlantic Monthly in July 1945, and republished again as an abridged version in September 1945 — before and after the U.S. nuclear attacks on Japan...
, Eugene Garfield
Eugene Garfield
Eugene "Gene" Garfield is an American scientist, one of the founders of bibliometrics and scientometrics. He received a PhD in Structural Linguistics from the University of Pennsylvania in 1961. Dr. Garfield was the founder of the Institute for Scientific Information , which was located in...
at the Institute for Scientific Information
Institute for Scientific Information
The Institute for Scientific Information was founded by Eugene Garfield in 1960. It was acquired by Thomson Scientific & Healthcare in 1992, became known as Thomson ISI and now is part of the Healthcare & Science business of the multi-billion dollar Thomson Reuters Corporation.ISI offered...
in the 1960s developed a comprehensive index of how scientific thinking propagates. His Science Citation Index
Citation index
A citation index is a kind of bibliographic database, an index of citations between publications, allowing the user to easily establish which later documents cite which earlier documents. The first citation indices were legal citators such as Shepard's Citations...
(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, such as Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
and Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
, were core for all of hard science. The same pattern does not happen with the humanities or the social sciences.
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. On the other hand, the set of "core journals" may vary more or less strongly with the individual researchers, and even more strongly along schools-of-thought divides. There is also a danger of over-representing majority views if journals are selected in this fashion.
Bradford's law is also known as Bradford's law of scattering and as the Bradford distribution. This law or distribution in bibliometrics can be applied to the World Wide Web
World Wide Web
The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...
.
Scattering
Hjørland and Nicolaisen (2005, p. 103) identified three kinds of scattering:- Lexical scattering. The scattering of words in texts and in collections of texts.
- Semantic scattering. The scattering of concepts in texts and in collections of texts.
- Subject scattering. The scattering of items useful to a given task or problem.
They found that the literature of Bradford's law (including Bradford's own papers) are unclear in relation to which kind of scattering is actually being measured.
Related laws and distributions
- Benford's lawBenford's lawBenford's law, also called the first-digit law, states that in lists of numbers from many real-life sources of data, the leading digit is distributed in a specific, non-uniform way...
, originally used to explain apparently non-random sampling - Lotka's law, describes the frequency of publication by authors in any given field.
- Pareto distribution, originally representing the distribution of wealth among individuals in a capitalist economic system.
- Power lawPower lawA power law is a special kind of mathematical relationship between two quantities. When the frequency of an event varies as a power of some attribute of that event , the frequency is said to follow a power law. For instance, the number of cities having a certain population size is found to vary...
, a general mathematical form for "heavy-tailed" distributions, with a polynomial density function. In this form, these laws may all be expressed and estimates derived. - Zeta distribution
- Zipf's law, originally used for word frequencies
- Zipf–Mandelbrot law