St. Lawrence, Brasfield, Shirley, Jefferson, Alleyne, and O’Brannon (1995) investigated the effects of an 8 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 condomprotected 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 one thousand 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.

Follow-up Follow-up Pretest Posttest 6 Months 12 Months 07 22 13 14 25 10 17 24 50 36 49 23 16 38 34 24 33 25 24 25 10 07 23 26 13 33 27 24 22 20 21 11 04 00 12 00 17 16 20 10

(a) Calculate and plot the means.

(b) Use the analysis of variance to draw the appropriate conclusions.