Editing Z-test (section)

==Applicability==
Because of the [[central limit theorem]], many test statistics are approximately normally distributed for large samples. Therefore, many statistical tests can be conveniently performed as approximate ''Z''-tests if the sample size is large or the population variance is known. If the population variance is unknown (and therefore has to be estimated from the sample itself) and the sample size is not large (''n'' < 30), the Student's ''t''-test may be more appropriate (in some cases, ''n'' < 50, as described below).