As a result of dog breeding for certain physical traits, many dog breeds have changed in the last 100 years. A dog breeder wants to measure the effects of breeding on the face length of the boxer breed using a hypothesis test. Suppose that the dog breeder has face length measurements (in inches) from a random sample of 40 female boxer dogs taken in 1915 and a random sample of 40 female boxer dogs taken in 2015. Which type of hypothesis test should the breeder use?