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If you would like to write for this, or any other Emerald publication, then please use our Emerald for Authors service information about how to choose which publication to write for and submission guidelines are available for all. Please visit www.emeraldinsight.com/authors for more information. About Emerald www.emeraldinsight.comEmerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of online products and additional customer resources and services.Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on Publication Ethics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation.Bradford distributions describe the relationship between 'journal productivities' and 'journal rankings by productivity'. However, different ranking conventions exist, implying some ambiguity as to what the Bradford distribution 'is'. A need accordingly arises for a standard ranking convention to assist comparisons between empirical data, and also comparisons between empirical data and theoretical models. Five ranking conventions are described including the one used originally by Bradford, along with suggested distinctions between 'Bradford data set', 'Bradford distribution', 'Bradford graph', 'Bradford log graph', 'Bradford model' and 'Bradford's Law'. Constructions such as the Lotka distribution, Groos droop (generalised to accommodate growth as well as fall-off in the Bradford log graph), Brookes hooks, and the slope and intercept of the Bradford log graph are clarified on this basis. Concepts or procedures questioned include: (1) 'core journal', from the Bradfordian viewpoint; (2) the use of traditional statistical inferential procedures applied to Bradford data; and (3) R(n) as a maximum (rather than median or mean) value at tied-rank values.The framework established is selectively illustrated in regard to a growing humanities literature, where particular attention was paid to generating a self-consistent and complete Bradford data set. No significant Groos effects were apparent, lending confirmation to the 'Law' as originally expressed by Bradford. Other empirical conclusions drawn are: (1) Brookes's parameter 's' is unsatisfactory as a measure of subject breadth and appears instead to reflect the size of the document corpus on a given subject, an alternative measure of subject breadth being suggested; (2) a terminal Brookes 'hook' for describing journals that (temporarily) produce zero articles provides a theoretically meaningful, although arbitrarily conditioned, extension to the Bradford graph; (3) the Lotka model of the related journal frequency distribution, which is unaffected by choice of rank convention, is more accurate than a logarithmic model of that distribution; and (4) the randomness underlying article production processes determines significant variations in journal...

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The dispersion or ‘scatter’ of documents over some set of values of a document attribute is usually described by means of a frequency distribution. When the attribute is qualitative an order distribution can be defined, as in the usual descriptions of Bradford's law. A more succinct description is offered by an order statistic, such as Singleton's index. A novel order statistic, the ‘adapted Gini index’, is introduced and related to the conventional form of Bradford's law. Some simple properties of it are described. An alternative index of dispersion, not an order statistic, based on the relative entropy of the frequency distribution is also defined. For sets of bibliographies such indices themselves have distributions, and it is suggested that, in particular, the distribution pertaining to an indexed data base provides an objective characterization of the data base in so far as indexing terms have been applied to the items in it. A variety of experimental data is reported. This includes the distribution of two indices for samples of bibliographies taken from British Technology Index and Index Medicus, and studies of the variation of the indices with time when the attribute is that of journal title. Whether a new area of knowledge becomes less or more dispersed in its journals as it progresses depends in part on which index is chosen to represent the dispersion, and on whether a series of cumulative or cross‐section bibliographies is chosen.