A professor assembles a group of volunteers to compare two methods of studying. One group spends an hour a day on the first subject (such as psychology), then an hour on the second (chemistry), and so forth. The other group goes back and forth, with a few minutes on each topic, repeating the sequence until completing the same total study time as the first group. At the end of a week, the professor tests each student's knowledge of each subject. Identify the independent variable and the dependent variable.