68. Elevated energy consumption during exercise continues after the workout ends. Because calories burned after exercise contribute to weight loss and have other consequences, it is important to understand this process. The paper Effect of Weight Training Exercise and Treadmill Exercise on Post-
Exercise Oxygen Consumption (Med. Sci. Sports Exercise, 1998: 518—522) reported the accompanying data from a study in which oxygen consumption (liters) was measured continuously for 30 minutes for each of 15 subjects both after a weight training exercise and after a treadmill exercise.
Subject 1 2 3 4 5 6 Weight (x) 14.6 14.4 19.5 24.3 16.3 22.1 Treadmill (y) 11.3 5.3 9.1 15.2 10.1 19.6 Subject 7 8 9 10 11 12 Weight (x) 23.0 18.7 19.0 17.0 19.1 19.6 Treadmill (y) 20.8 10.3 10.3 2.6 16.6 22.4 Subject 13 14 15 Weight (x) 23.2 18.5 15.9 Treadmill (y) 23.6 12.6 4.4

a. Construct a comparative boxplot of the weight and treadmill observations, and comment on what you see.

b. Because the data is in the form of (x, y) pairs, with x and y measurements on the same variable under two different conditions, it is natural to focus on the differences within pairs: d1  x1  y1, . . . , dn  xn  yn. Construct a boxplot of the sample differences. What does it suggest?