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 contains the
change in heart rate; a positive number means that heart rate went up
and a negative number means that heart rate went down.