The "Statistics::Contingency" class helps you calculate several useful
statistical measures based on 2x2 "contingency tables". I use these measures
to help judge the results of automatic text categorization experiments, but
they are useful in other situations as well.

The general usage flow is to tally a whole bunch of results in the
"Statistics::Contingency" object, then query that object to obtain the
measures you are interested in. When all results have been collected, you
can get a report on accuracy, precision, recall, F1, and so on, with both
macro-averaging and micro-averaging over categories.

WWW: http://search.cpan.org/dist/Statistics-Contingency/