Also called the Law of Scatter and Bradford's Distribution.
S(amuel) C(lement) Bradford proposed a formula that described this phenomenon: on any one subject, a few group of core journals will provide 1/3 of the articles on that subject, a medium number of less-core journals will provide another 1/3 of the articles on that subject, and a large number peripheral journals will provide the final 1/3 of the articles on that subject.
For example, if you did a literature search on the topic of library service to the visually handicapped and you found 300 citations, according to Bradford Law of Scattering you'd discover that 100 of those citations came from a core group of 5 journals, another 100 citations came from a group of 25 less-core journals, and the final 100 citations came from 125 peripheral journals.
Bradford expressed his law with this formula: 1:n:n^2
There are many arguments about the validity of Bradford's Law and how accurate his formula is. To me, it sounds similar to any of the number of information science laws (e.g., Zipf's, Pareto's, Mandelbrot's, Lotka's, Leimkuhler's) that describe the phenomena of the few generating the many.
These laws are usually described as Power Laws, because of the inverse relationships between the values being measured. Charts of power laws show a few outliers at the high end of the spectrum and a long tail of many objects at the low end of the spectrum.
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