6.7.11 Researchers were interested in the short-term effect that caffeine has on heart rate. They enlisted a group of volunteers and measured each person's resting heart rate. Then they had each subject drink 6 ounces of coffee. Nine of the subjects were given coffee containing caffeine, and 11 were given decaffeinated coffee. After 10 minutes each person's heart rate was measured again. The data in the table show the change in heart rate; a positive number means that heart rate went up, and a negative number means that heart rate went down.47 Use these data to construct a 90% confidence interval for the difference in mean effect that caffeinated coffee has on heart rate, in comparison to decaffeinated coffee. [Note: Formula (6.7.1) yields 17.3 degrees of freedom for these data.] Using the interval computed in part (a) to justify your answer, is it reasonable to believe that caffeine may not affect heart rates? Using the interval computed in part (a) to justify your answer, is it reasonable to believe that caffeine may affect heart rates? If so, by how much? Are your answers to (b) and (c) contradictory? Explain. Caffeine Decaf 28 26 11 1 3 0 14 4 2 4 4 14 18 16 2 8 2 0 18 10 n 9 11 Ybar 7.3 5.9 s 11.1 11.2 SE 3.7 3.4