(About that Statistics::Table::F module:) I must admit the docs of that module are very minimal. Moreover, I tried to install it, but that doesn't work. I'm sorry that I've given you a pointer that I never used myself.

The BSP package seems to have a really specialized use of bigrams, I don't whether it can be used as-is for your application. (update) After paging through it, I still can't easily see where the bigram stops and the algoritm comes in.

To make it up to you, I will program your F-test.

Jeroen
"We are not alone"(FZ)

Update: There is javascript code to be found here.

...time passes and I have parsed that javascript into perl: Fisher's Exact test (probability of 2x2 tables)