Kent Mulliner (and others from OhioLINK) have proposed that the shape of
the use curve is much greater for Ohio than for other reports in the
literature (70:30 vs. 80:20).  This has been used to justify the purchase
of the proverbial Big Deals.  The OhioLink data look this way because all
80 or so library's usage data are aggregated together.  Taken individually,
the usage patterns are closer to 80:20, or even above 90:10.  I verified
this using NERL data (30 libraries), and then OhioLink data.  So, the
pattern that Kent is reporting is a statistical artifact of aggregating
multiple libraries into a single dataset.  If he analyzed the libraries
independently, he will notice very different results.  I demonstrate this
point in my article.

Patterns in Electronic Journal Usage:  Challenging the Composition of
Geographic Consortia.
College and Research Libraries
Vol 63, n6, Nov 2002
The preprint can be downloaded from:
http://people.cornell.edu/pages/pmd8/Davis_Consortia.pdf

Respectfully submitted
Phil Davis
Cornell University

----------2
Date: Thu, 05 Jun 2003 18:21:59 -0400
From: Kent Mulliner <mulliner@ohio.edu>
Subject: Re: Bradford distribution, 80/20, and larger samples

Without any pretense at statistical sophistication, in a paper I presented at
the Charleston Conference last November, I offered statistics on long-term
(four years), statewide electronic journal usage data for OhioLINK.  For
Elsevier titles, that indicated a 70:30 usage ratio.  Importantly, a closer
analysis of the data indicated that variation in usage was greatest in
the first year (whether a learning curve or a kid in a candy shop were
competing hypotheses) with correlation coefficients of .29 and .42 for
the middle and bottom thirds with usage after four years.  Also,
variation in usage year to year and over four years was greatest
in the middle third of  the title distribution.  Since this was based on the
full Elsevier buffet (the same 1,182 titles), it suggested that there were
of course titles on the bottom and to which we had (in most, but not all,
cases) not subscribed which could be lost with little impact and
similarly the most used list was fairly clear with titles to which we
subscribed (or would have if we could afford it).  It was exactly
in the middle, where we (outside of the big deal) would have liked to
keep some and shed some that usage varied most from year to year.
This year's cherry would become next year's lemon and the following
year's prune.

One caveat that I stressed.  While the usage extends over four years
(nearly an eon in e-journal time), usage continues to grow year after
year (by about 200,000 per year) so we are hardly looking at a mature
situation.

K. Mulliner       Collection Development Coordinator

Ohio University Libraries                       PHONE:  740-593-2707
Athens, OH 45701-2978, USA      FAX:    740-593-2692
mulliner@ohio.edu