Usually a two-sample t test is applied to test for a significant difference between two population means based on the two samples. For example, consider the data in Table 1. Twenty patients with high blood pressure are randomly assigned to two groups of 10 patients. Patients in Group 1 are assigned to receive placebo, while patients in Group 2 are assigned to receive Drug A. Patients’ systolic blood pressures (SBPs) are measured before and after treatment, and the differences in SBPs are recorded in Table 1. A two-sample t test would be an efficient method for testing the hypothesis that drug A is more effective than placebo when the differences in before and after measurements are normally distributed. However, there are usually more than two ...