The Long Tail: A Usage Analysis of Pre-1993 Print Biomedical Journal Literature*
Starr, Susan, Williams, Jeff, Journal of the Medical Library Association
Objective: The research analyzes usage of a major biomedical library's pre-1993 print journal collection.
Methodology: In July 2003, in preparation for a renovation and expansion project, the Biomedical Library at the University of California, San Diego, moved all of its pre-1993 journal volumes off-site, with the exception of twenty-two heavily used titles. Patrons wishing to consult one of these stored volumes could request that it be delivered to the library for their use. In the spring of 2006, an analysis was made of these requests.
Results: By July of 2006, 79,827 journal volumes published in 1992 or earlier had been requested from storage. The number of requests received declined with age of publication. The usage distribution exhibited a "long tail": 50% of the 79,827 requests were for journal volumes published before 1986. The availability of electronic access dramatically reduced the chance that corresponding print journal volumes would be requested.
Conclusions: The older biomedical print journal literature appears to be of continued value to the biomedical research community. When electronic access was provided to the older literature, demand for older print volumes declined dramatically.
Bibliometricians have long studied the decline in the use of scientific literature with age, also known as obsolescence, in hopes that their studies would shed light on the reasons for any decay in the utility of information and, thus, on the nature of scholarly communication itself. These studies suggest that use of scientific literature, in general and medical literature, in particular, declines rapidly with time [1, 2]. Information scientists have hypothesized that this decline reflects two distinct stages in the use of the journal literature. In the first stage, which occurs in the first few years after publication, readers scan the recent literature to stay up to date on general trends and to maintain proficiency in their fields of interest. The need to frequently peruse current literature, sometimes referred to as the "immediacy effect" , is likely responsible for the extremely heavy use of newer material reported in the above-referenced studies. In later years, journals are consulted largely by readers looking up citations found in other articles or identified when searching indexing and abstracting services such as PubMed or search engines like Google Scholar. The high levels of usage generated in early years by current awareness needs declines to a much lower, but possibly steady, pattern of consultation. Because of the immediacy effect, only a relatively few years of any journal may account for most of its use.
One important consideration for librarians is that most bibliometric studies that find a rapid decline in the use of the literature a few years after publication do not study actual journal usage. Instead, they document declines in citation frequency over time and assume that this decline reflects an actual decline in use of the literature. This distinction is particularly important for libraries considering whether to retain older literature in their collections. Line notes, "It is not known how useful references and citations may be as indicators of use probability, nor how usage patterns differ between libraries whether of the same or different types" .
For medical librarians, an important exception to Line's statement can be found in the work of Tsay, who reported that the "mean use half-life," or the average time needed for a publication in her collection to experience half of its lifetime of use, was 3.43 years after publication . In a subsequent study, Tsay  reported a statistically significant correlation between actual usage and impact factor. Sullivan et al. not only found a similar mean use half-life when tabulating usage over a ten-year period for Stanford's journal collection, but also verified that the rapid decline in usage of the literature with time is not just a function of the size of the journal literature . …