Definition t-test
The t-test is a commonly used test to compare the mean value of a distribution against a chosen null hypothesis. Most commonly, the t-test is either used to compare means of two different groups to assess if they are significantly different from each other (null hypothesis = mean of group A is different from the mean of group B), or to assess the significance of regression coefficients (null hypothesis = the coefficient equals 0). Quite importantly, the t-test requires only the standard deviation of the observations, and not the whole population's standard deviation. This is the main difference between the t-test and the z-test.
Please note that the definitions in our statistics encyclopedia are simplified explanations of terms. Our goal is to make the definitions accessible for a broad audience; thus it is possible that some definitions do not adhere entirely to scientific standards.