This statistic is a measure on a random sample (or pair of samples) in which a mean (or pair of means) appears in the numerator and the numerator's standard deviation appears in the denominator.

This is the formula for the statistic (z) when it is used to test the statistical hypothesis that two random samples come from populations with means equal to

It is assumed that the values of are both known.

If these calculations yield a value of (z) that is sufficiently different from zero, the test is considered to be statistically significant.

This is the formula for the statistic (z) when it is used to test the statistical hypothesis that two random samples come from populations with means equal to

It is assumed that the values of are both known.