simple to design a filter that does not underblock, it is currently impossible, given the

Internet's size, rate of growth, rate of change, and architecture, and given the state of the

art of automated classification systems, to develop a filter that neither underblocks nor

overblocks a substantial amount of speech.  The more effective a filter is at blocking Web

sites in a given category, the more the filter will necessarily overblock.  Any filter that is

reasonably effective in preventing users from accessing sexually explicit content on the

Web will necessarily block substantial amounts of non sexually explicit speech.  

4.  Attempts to Quantify Filtering Programs' Rates of Over  and Underblocking 

The government presented three studies, two from expert witnesses, and one from

a librarian fact witness who conducted a study using Internet use logs from his own

library, that attempt to quantify the over  and underblocking rates of five different

filtering programs.  The plaintiffs presented one expert witness who attempted to quantify

the rates of over  and underblocking for various programs.  Each of these attempts to

quantify rates of over  and underblocking suffers from various methodological flaws.  

The fundamental problem with calculating over  and underblocking rates is

selecting a universe of Web sites or Web pages to serve as the set to be tested.  The

studies that the parties submitted in this case took two different approaches to this

problem.  Two of the studies, one prepared by the plaintiffs' expert witness Chris Hunter,

a graduate student at the University of Pennsylvania, and the other prepared by the

defendants' expert, Chris Lemmons of eTesting Laboratories, in Research Triangle Park,

North Carolina, approached this problem by compiling two separate lists of Web sites,

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