Performing a Z-test

When you have over 30 observations, you should use a Z.TEST() over a T.TEST() to compare means. Listed to your right is some salary data of U.S Government workers. Your job is to conduct a hypothesis test using the Z-test.

Here you want to know if the sample average salary is less than or equal to the government's published average. Are you going to compare one or two tails of the distribution? The <= operator is exploring a single direction away from the value. Thus, this is a one-tailed test.

A Z-test accepts the data range followed by the population's mean - in this case, the government's published average salary. You can also add the population's standard deviation as a third parameter. If you don't, Z.TEST() will use the sample's standard deviation.