A doctor is interested in how exercise affects sleep, so she conducts an experiment. 30 healthy individuals are randomly assigned to three groups: light exercise, moderate exercise, and heavy exercise. To collect her data, she has the light exercise group come into her facility in the morning to perform the routine. Then she has the moderate exercise group perform the routine after lunch. Finally, the heavy exercise group performs their routine in the late afternoon. She records the number of hours each participant sleeps that night. a) What is/are the factor(s) in this experiment?