- Population data from which the sample data are drawn are normally distributed.
- The variances of the populations to be compared are equal.

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.