Statistical tests assume that certain conditions are met, in order for the test to be accurate. The primary assumptions for the t-test are:
Actually, empirical studies of the t-test have demonstrated that these assumptions can be violated to an amazing degree without substantial effect on the results.

For a discussion of the t-test, please see the following text, pages 319-323:

Hays, W. L. (1963).  Statistics.  New York:  Holt, Rinehart and Winston.

Return to the discussion of the Posttest-Only Control Group Design.