and Finnell’s studies analyzed, this removes the possibility of bias resulting from the study author’s selection of the universe of sites to be reviewed.  We find that the Lemmons and Hunter studies are of little probative value because of the methodology used to select the sample universe of Web sites to be tested.  We will therefore focus on the studies conducted by Finnell and Biek in trying to ascertain estimates of the rates of over- and underblocking that takes place when filters are used in public libraries.  The government hired expert witness Cory Finnell to study the Internet logs compiled by the public libraries systems in Tacoma, Washington; Westerville, Ohio; and Greenville, South Carolina.  Each of these libraries uses filtering software that keeps a log of information about individual Web site requests made by library patrons.  Finnell, whose consulting firm specializes in data analysis, has substantial experience evaluating Internet access logs generated on networked systems.  He spent more than a year developing a reporting tool for N2H2, and, in the course of that work, acquired a familiarity with the design and operation of Internet filtering products.

The Tacoma library uses Cyber Patrol filtering software, and logs information only on sites that were blocked.  Finnell worked from a list of all sites that were blocked in the Tacoma public library in the month of August 2001.  The Westerville library uses the Websense filtering product, and logs information on both blocked sites and non-blocked sites.  When the logs reach a certain size, they are overwritten by new usage logs.  Because of this overwriting feature, logs were available to Finnell only for the relatively short period from October 1, 2001 to October 3, 2001.  The Greenville library uses N2H2’s filtering product and logs both blocked sites and sites that patrons accessed.  The logs contain more than 500,000 records per day.  Because of the volume of the records, Finnell restricted his analysis to the period from August 2, 2001 to August 15, 2001.

Finnell calculated an overblocking rate for each of the three libraries by examining the host Web site containing each of the blocked pages.  He did not employ a sampling technique, but instead examined each blocked Web site.  If the contents of a host Web site or the pages within the Web site were consistent with the filtering product’s definition of the category under which the site was blocked, Finnell considered it to be an accurate block.  Finnell and three others, two of whom were temporary employees, examined the Web sites to determine whether they were consistent with the filtering companies’ category definitions.  Their review was, of course, necessarily limited by:  (1) the clarity of the filtering companies’ category definitions; (2) Finnell’s and his employees’ interpretations of the definitions; and (3) human error.  The study’s reliability is also undercut by the fact that Finnell failed to archive the blocked Web