Originally Posted by

**chiro** If you are talking about underlying distributions then you just need to know what kind of test statistic you are using.

The T distribution typically uses the sample mean and sample variance while a lot of results for using Z are based on the Central Limit Theorem and the Asymptotic results like the Wald Statistic and others.

If you know what kind of information you are using and the nature of the test statistic, you will know whether its a t-distribution or a Normal distribution.