In a study to determine which factors predict who will benefit from treatment for bulimia nervosa, 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 post-treatment, 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 post-treatment mean.
c. In Section 10.4, we will introduce small-sample techniques 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 population means represented by the results in the table?

Pretreatment Posttreatment Follow-up 20.3 5.0 21 26.6 Sample Mean X Standard Deviations Sample Size n 74 21 27.7 8.2 20