15. Does the Diet Work? When 40 people used the Atkins diet for one year, their mean weight change was 22.1 lb (based on data from “Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for Weight Loss and Heart Disease Reduction,” by Dansinger, et al., Journal of the American Medical Association, Vol. 293, No. 1). Assume that the standard deviation of all such weight changes is s 5 4.8 lb and use a 0.05 significance level to test the claim that the mean weight change is less than 0.

Based on these results, does the diet appear to be effective? Does the mean weight change appear to be substantial enough to justify the special diet?