For example, when we are comparing the means of two populations, if the sample size is less than 30, then we use the t-test. If the sample size is greater than 30, then we use the z-test.

Which test is used when sample size is less than 30?

Z-tests are closely related to t-tests, but t-tests are best performed when an experiment has a small sample size, less than 30. Also, t-tests assume the standard deviation is unknown, while z-tests assume it is known.

What does a sample size of 30 mean?

A sample size of 30 of is considered to be *typically large enough* for repeatedly sampled means to be *approximately normally distributed*.