Thanks to John McDonald who provided some excellent reading on this
topic.  It was believed that the Bradford curve would look different for
different subject collections (because it would reveal unique sociological
differences between then).  Drott and Griffith did a meta analysis of
numerous studies that indicated that the slope and intercept of the line is
not dependent upon the subject of the literature, time period, or searching
technique.  In other words, it must rely on some probalistic mechanism
underlying the law.

Drott, M. C., & Griffith, B. C. (1978). An Empirical Examination of
Bradford's Law and the Scattering of Scientific Literature. Journal of the
American Society for Information Science, 29(5), 238-243.

--Phil Davis
Life Sciences Librarian, Cornell University

At 09:44 AM 6/6/2003 -0400, you wrote:
>----------1
>Date: Thu, 5 Jun 2003 14:53:30 -0700
>From: jmcdonald@library.caltech.edu
>Subject: Re: Bradford distribution, 80/20, and larger samples
>
>
>
>Thanks to Steve for bringing up these intriguing observations.  When
>considering the Bradford distribution and the 80/20 rule, it is important to
>remember that the shape of the distribution curve is dependent on the
>internal structure of the data (Oluic-Vukovic 1997) and as the number of
>accesses increases towards infinity the concentration of titles increases as
>well (Egghe 1987).  An aggregated database that features 500,000 accesses
>and 8000 titles has an extremely high concentration per number of accesses,
>resulting in a lower proportion of items covering 80% of the accesses.  In
>addition, the internal structure of the data skews the distribution since an
>aggregated database will contain unequal numbers of articles per journal.
>
>An institution that has 1 million accesses on the same database will have an
>even lower % of titles accounting for 80% of the accesses.
>
>
>John McDonald
>Acquisitions Librarian
>California Institute of Technology
>
>
>Bradford's Distribution: From the Classical Bibliometric ''Law'' to the More
>General Stochastic Models
>Vesna Oluic-Vukovic
>JOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE. 48(9):833-842, 1997
>
>
>Pratt's Measure for some Bibliometric Distributions and its Relation with
>the 80/20 Rule
>Leo Egghe
>JOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE. 38(4):288-297, 1987