Bradford's law of scattering
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This entry is out of date, and will not be updated, June 2017
Bradford's law of scattering (also Bradford's law and the Bradford distribution), is one of a handful of so-called bibliometric laws (also Lotka's and Zipf's law). The law of scattering describes how the literature on a particular subject is scattered or distributed among portions or segments of the journal literature. Bradford formulated the law in the 1930s and claimed that in each subject or domain "there are a few very productive periodicals, a larger number of more moderate producers, and a still larger number of constantly diminishing productivity..." According to Garfield (1980), "...One of the statistical tools related to Bradford’s law is the Pratt index. This index purports to measure the degree to which papers on a given subject are concentrated within a journal collection. Then there’s Lotka’s law, which describes the productivity distribution among scientists, as, for example, how many scientists will author ten or more papers.
The law of scattering or dispersal is calculated in a given subject field over a period of time:
In other words, Bradford's is a law of diminishing returns and scattering (or dissemination). According to Bates (2002), extensive literature exists on information searching theory and techniques coupled with the Bradford distribution. To reiterate, the law tells us that information on a subject is dispersed in a characteristic and robust pattern, and that by identifying patterns, it is possible to reveal a consistency of scattering.
Types of scattering
Hjørland and Nicolaisen (2005, p. 103) identified three types/kinds of scattering:
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.
Searching and information science
Research has been made in library and information science (LIS) about how the scholarly literature is scattered; for example, how articles on a given subject is scattered among scientific journals. One can also use the opposite expression: how articles on a given subject are concentrated among a corpus of journals. Generally speaking, Bradford's law aims to show how documents are scattered (or concentrated) in different literatures. The question is whether the law is applicable in 2013, given all the changes in publishing in the open access and social media eras.
For a thorough search on a specific topic, a large number of the relevant articles will be concentrated in a small number of journals. The rest of the articles will be scattered over a large number of journals that have only 1 or 2 articles each on the topic. According to Brookes, "...any index terms that are assigned to documents also follow a Bradford distribution because those terms most frequently assigned become less and less specific and therefore increasingly ineffective in retrieval."
In taking a broader view of the Bradford phenomenon, authors may make conscious decisions about where to publish their work. They may choose to publish in many different places (scattered) or within a few journals (concentrated). There may be individual variation in this form of publishing behaviour but general patterns can be found to reflect underlying norms, cultures and constraints. Some fields are more interdisciplinary, some cultures more open; some fields have a high degree of consensus about which journals are the most important and so on. In some fields, national traditions are important, in other not.
The re-ranking of content to the most frequent sources (extracting the nucleus) can be a helpful access mechanism for browsing and initial search stages, especially for novice researchers in a discipline.
One of a handful of bibliometric laws, Lotka's law describes the frequency of publication by authors in a given field. It states that " . . . the number (of authors) making n contributions is about 1/n² of those making one; and the proportion of all contributors, that make a single contribution, is about 60 percent".
A related concept to Bradford's law is Zipf's law which states that given some corpus of natural language utterances, the frequency of any word is inversely proportional to its rank in a frequency table. Thus the most frequent word will occur approximately twice as often as the second most frequent word, three times as often as the third most frequent word, etc.
According to Garfield (1980), "...One of the statistical tools related to Bradford’s law is the Pratt index. This index purports to measure the degree to which papers on a given subject are concentrated within a journal collection."