HELP - Greenhouse-Geisser (G-G) correction

I am attempting to evaluate the data given in a research article. The article is evaluating two treatment groups, and in attempting to show that one of the groups has a trend towards a more pronounced increase of the desired behavior (verses the other group) it includes the following: (G-G - corrected F[3.7,1.3]=9.8, P<0.06). I've looked through textbooks on statistics for behavioral sciences and other resources online and I have been unable to find anything useful. Can someone please advise?