30. Bulimia An article in the British Journal of Clinical Psychology indicates that self-esteem was an important predictor of those who will benefit from treatment for bulimia.4 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 pretreatment mean is less than 25.

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

c. In Section 10.3, we will introduce small-sample techniques for making inferences about the difference between two population means. Without a formal statistical test, what might you conclude about the differences among the three sampled population 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