Statistical Methods for Psychology

Exercises 511

were measured at Pretreatment, Posttreatment, and a 3.5 month Follow-up. The data below

closely approximate the data that they collected, and the dependent variable is a measure of

PTSD.

SIT PE SC

Pre Post Followup Pre Post Followup Pre Post Followup

19 6 1 20 5 0 12 14 18

28 14 16 21 18 21 27 18 9

18 6 8 36 26 17 24 19 13

23 6 11 25 11 9 32 21 11

21 6 13 26 2 7 26 20 18

24 10 8 30 31 10 18 20 26

26 10 7 19 6 11 38 35 34

15 6 13 19 7 5 26 22 22

18 8 6 22 4 4 23 10 8

34 13 8 22 17 20 22 19 19

20 10 16 24 19 1 34 27 23

34 10 1 28 22 16 22 15 12

29 16 23 29 23 20 27 18 13

33 19 39 27 15 20 23 21 19

22 7 16 27 7 3 26 18 13

a. Run a repeated measures analysis of variance on these data.

b. Draw the appropriate conclusions.

14.21 Using the data from Exercise 14.20 use SPSS to run a mixed models analysis of variance,
specifying an appropriate form for the covariance matrix, and compare the results with
those you obtained in Exercise 14.20.

14.22 The following data come from Exercise 14.20 with some observations deleted. (An entry of
“999” represents a missing observation.)

SIT PE SC

Pre Post Followup Pre Post Followup Pre Post Followup

19 6 1 20 5 0 12 14 18

28 14 16 999 999 21 27 18 9

18 6 8 36 26 17 24 999 13

999 6 11 25 11 9 32 21 11

21 6 13 26 999 7 26 20 18

24 10 8 30 31 10 18 20 26

26 10 999 19 6 11 38 35 34

15 6 13 19 7 999 26 22 999

18 8 6 22 4 999 23 10 8

34 13 8 22 17 20 22 19 19

20 999 999 24 19 1 34 999 999

34 10 1 28 22 16 22 15 12

29 16 23 29 23 20 27 18 13

33 19 39 27 15 20 23 21 19

22 7 16 27 7 3 26 18 13

a. Analyze these data using a standard repeated measures analysis of variance.

b. How do your results differ from the results you found in Exercise 14.20?

14.23 Now analyze the data in Exercise 14.22 using a mixed models approach, an appropriate
form for the covariance matrix. How do those results differ from the results you found in
Exercise 14.22?