Julius has conducted a very small study of the amount of sleep his dorm mates get each night. He believes that those who are on one of the school's sports teams will get more sleep (measured in hours per night) than those who are not. Julius surveyed 12 people. Of these, 6 played on a sports team and 6 did not. The descriptive statistics from his survey are given below.

PLAYS SPORTS (Sample 1) 8, 9, 8, 7, 8, 7 DOES NOT PLAY SPORTS (Sample 2) 6, 6, 5, 7, 7, 6

What is the dependent variable?