The T-Test test is used to determine whether the mean of a numeric variable is significantly different from zero or some other specified value. The test can also be used to test for differences between means measured on matched samples (paired T-test), for example, between the means of two variables both obtained from the same sample of respondents. Examples can include trials of two drugs where the same person receives each drug at different times and observations are taken on their resulting condition after using each drug. The test might also be employed to study a comparison of a group of students’ competencies in two areas (verbal and mathematical, for example) by analyzing two sets of test results.

The pairing of data must be taken into account as, for example, it is necessary to adjust for each particular patient's general reaction to treatments; similarly for each pupil's overall academic competence (students obtaining better marks in one test could be more likely to do well in the other).