Chapter 8.8, Problem 80E

Although there are many treatments for bulimia nervosa, some subjects fail to benefit from treatment. In a study to determine which factors predict who will benefit from treatment, Wendy Baell and E. H. Wertheim¹² found that self-esteem was one of the important predictors. The mean and standard deviation of posttreatment self-esteem scores for n = 21 subjects were $\bar{y}$= 26.6 and s = 7.4, respectively. Find a 95% confidence interval for the true posttreatment self-esteem scores.