In the study discussed in Exercise 18.10, the authors also ran a control group under the same conditions, but without the BST intervention. Those data (for males) follow.

Exercises 18.10

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.

Transcribed Image Text:

Pretest Posttest Follow-up Six Months Follow-up 12 Months 00 69 05 04 35 24 08 07 51 25 59 40 00 53 00 45 888 8 2 8 48 00 56 00 14 00 00 8 8 8 8 8 = 3 05 00 00 00 00 09 37 08 26 00 15 16 33 16 888 m 00 36 02 (a) Calculate the means for these data and plot them on the same graph used in Exercise 18.9. (b) Run the analysis of variance on these data.