[Extract] Bradford's Law of Scattering is a law of diminishing returns and scattering. Bradford formulated the law in 1948 and claimed that for a given subject area “there are a few very productive periodicals, a larger number of more moderate producers, and a still larger number of constantly diminishing productivity”. For any single issue, or subject area, the top third (Zone 1 or core) represents the journals that are the most frequently cited in the literature of that subject and that are, therefore, likely to be of highest interest to researchers in the discipline. The middle third (Zone 2) includes the journals that have had an average amount of citations, and the bottom third (Zone 3 or tail) comprises the long tail of journals that are seldom cited and regarded as of marginal importance to the subject. Researchers have defined a subject area in lexical, semantic, and subject scattering terms, and some argue that problems in defining “subject” may not matter, provided it is applied consistently.
Nash-Stewart, C. E., Kruesi, L. M., & del Mar, C. B. (2012). Does bradford's law of scattering predict the size of the literature in cochrane reviews? Journal of the Medical Library Association : JMLA, 100(2), 135-138. https://doi.org/10.3163/1536-5050.100.2.013