St. Lawrence, Brasfield, Shirley, Jefferson, Alleyne, and O€™Brannon (1995) investigated the effects of an eight-week Behavioral Skills Training (BST) program aimed at reducing the risk of HIV infection among African-American adolescents. The study followed males and females from a pretest to a 12-month follow-up, recording the frequency of condom-protected sex. (They also had a control condition, but I am going to look only at the males in the BST condition for this exercise.) The actual dependent variable is 1,000 times the natural logarithm of the frequency of protected sex. (I multiplied the log by 1,000 to eliminate decimal values.) The data for males follow.

(a) Calculate and plot the means.
(b) Use the analysis of variance to draw the appropriate conclusions.

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Pretest Posttest Follow-up Follow-up 6 Months 12 Months 3 0 24 24 26 10 34 24 27 24 12 10