In Exercises 5-20, assume that the two samples are independent simple random samples selected from normally distributed populations, and do not assume that the population stan-dard deviations are equal. (Note: Answers in Appendix D include technology answers based on Formula 9-1 along with "Table" answers based on Table A-3 with df equal to the smaller of n11 and n21.)

9. Magnet Treatment of Pain People spend around $5 billion annually for the purchase of magnets used to treat a wide variety of pains. Researchers conducted a study to determine whether magnets are effective in treating back pain. Pain was measured using the visual analog scale, and the results given below are among the results obtained in the study (based on data from "Bipolar Permanent Magnets for the Treatment of Chronic Lower Back Pain: A Pilot Study," by Collacott, Zimmerman, White, and Rindone, Journal of the American Medical As-sociation, Vol. 283, No. 10). Higher scores correspond to greater pain levels.

a. Use a 0.05 significance level to test the claim that those treated with magnets have a greater mean reduction in pain than those given a sham treatment (similar to a placebo).

b. Construct the confidence interval apropriate for the hypothesis test in part (a).

c. Does it appear that magnets are effective in treating back pain? Is it valid to argue that mag-nets might appear to be effective if the sample sizes are larp