The Sixty-Minute Guide to Evaluating Comparative Test Data
http://www.stc.org/edu/55thConf/download.asp?ID=39

Hughes, Michael A.
STC Proceedings
2008

Abstract:

Mary wants to compare the average registration times between the two versions to see if the second version is faster than the first. The method typically used when comparing averages is called a t-test of independent means.