The logic and computational details of two-sample t-tests
are described in Chapters 9-12 of the online text Concepts & Applications of Inferential Statistics.
For the independent-samples t-test,
this unit will perform both the "usual" t-test,
which assumes that the two samples have equal variances, and the alternative t-test,
which assumes that the two samples have un
equal variances. (A good formulaic summary of the unequal-variances t-test can be found on the StatsDirect web site. A more thorough account appears in the online journal Behavioral Ecology.)