T-Test

The t-test is a statistical test that compares the means of two groups of observations. The observations should be randomly assigned to the two groups, so that any difference in response is due to the treatment and not to other factors. For instance in a medical study patients with high blood pressure are randomly assigned to a placebo group and a treatment group. The patients in the placebo group receive an inactive pill and the patients in the treatment group receive a new drug that is expected to lower blood pressure. After treating the subjects, the t test is used to compare the average blood pressures level for the placebo group and the treatment group.