Some serious work on nine databases maintained by the National Library of Medicine is reported. An empirical investigation of the patterns of use of a university Web-based catalog was conducted for 479 days. Cooper analyzed approximately 2.5 million sessions, during which about 7.4 million search statements were executed.
Three categories of users are identified:
individuals who perform a search of the catalog,
tourists who look only at opening pages, and
Web spiders that come to the site to index pages.
Sixty-two percent of the sessions were for users who performed a search, 27 percent were from spiders, and 11 percent were for tourists. The average search session lasted about five minutes when the study began, and had increased to about ten minutes 16 months later. An average search consisted of about 1.5 pre-search actions lasting about 25 seconds per session. The latter two categories are in the range of 35 to 37 seconds per session each.
Over the study period, the number of spider and tourist sessions remained relatively constant, but the number of real sessions continued to grow, albeit erratically, with fluctuations at semester and quarter deadlines. Users made very few errors and made fewer requests for help over time. Numbers of searches and display actions per session were consistent after the initial learning period (about six months). There were significant differences in user behavior when searching different databases. Users performed about one search per session of the Med database, and about 1.5 on the Cat database.
