People living near an airport claim that the jets have hurt their hearing. An audiologist decides to see if their claim is justified. No tests of hearing were made before they moved to the airport vicinity, so he has to use different people for comparisons. He selects people who live in the same town, sufficiently far from the airport so that they cannot hear the planes taking off and landing. He wants to compare the hearing of the two groups to test the claim of the people who live near the airport. Both groups are given hearing tests that yield a score of hearing loss relative to some norms. The test scores range from 0 to 40. Which statistic should be used?