A study was conducted to find out whether relaxation training, aided by biofeedback as well as meditation, could help in reducing high blood pressure. Subjects were randomly allocated to the biofeedback group or a control group. The biofeedback group received training for eight weeks. The table reports the reduction in systolic blood pressure (mm Hg) after eight weeks.
Biofeedback Control
n 99 93
y bar 13.8 4.0
SE 1.34 1.30
(a) Develop a 95% confidence interval for the difference in mean response.
(b) Suppose we are worried that the blood pressure data do not come from normal distributions. Does this mean that the confidence found in (a) is not valid? Why or why not?