T-test is generally used to compare sample means to determine if there is evidence that the means of the corresponding populations differ. The most common types are paired t-test, independent-sample t-test, and one-sample t-test.

One-sample t-test is used to compare the mean of a sample to a hypothesized population mean.

Paired t-test is used when the two scores being compared are paired or somewhat matched (i.e., they are not independent of one another) or if the two scores are repeated measures (e.g., within-groups design). An example of repeated measures is comparing the mean difference in a group of people who have taken a pretest and a posttest before and after an intervention.

An independent samples t-test is used to compare the means of two independent or unrelated groups (e.g., between-groups design) on an approximately normal dependent variable.