An economics instructor would like to test the theory that spraying lavender essential oil in a room while studying will improve test scores. One group of participants studies in a room that releases 2 ounces of lavender every 3 to 4 hours. The second group studies in a room that does not release any essential oils. Both groups study the same amount of time leading up to all course exams. The instructor records the number of points each group gets on a total of 4 exams during a 5 week summer course. Which best describes the scale of measurement for the dependent variable in this experiment.