10.13 Bulimia 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, an article in the British Journal of Clinical Psychology indicates that self-esteem was one of these important predictors. The table gives the mean and standard deviation of self- esteem scores prior to treatment, at posttreatment, and during a follow-up:

a. Use a test of hypothesis to determine whether there is sufficient evidence to conclude that the true pre- treatment mean is less than 25.

b. Construct a 95% confidence interval for the true posttreatment mean.

c. In Section 10.4, we will introduce small-sample tech- niques for making inferences about the difference between two population means. Without the formality of a statistical test, what are you willing to conclude about the differences among the three sampled popu- lation means represented by the results in the table?

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Pretreatment Posttreatment Follow-up Sample mean x 20.3 26.6 27.7 Standard deviation s 5.0 7.4 8.2 Sample size n 21 21 20