Statistical Methods for Psychology

Exercises 459

13.31 An educational researcher wanted to test the hypothesis that schools that implemented strict

dress codes produced students with higher academic performance. She randomly selected

7 schools in the state with dress codes and 7 schools that had no dress code. She then ran-

domly selected 10 students within each school and noted their performance on a standard-

ized test. The results follow.

Dress Code No Dress Code

School 1 2 3 4 5 6 7 8 9 10 11 12 13 14

91 75 80 84 59 62 87 69 72 78 66 67 52 63

78 73 77 92 67 93 78 74 56 77 55 82 71 65

86 65 70 78 68 83 83 67 71 75 58 76 73 75

70 68 68 78 64 78 79 64 92 56 73 78 68 82

78 70 70 77 75 65 53 61 88 84 55 87 65 77

48 60 69 76 74 71 66 76 64 83 70 87 69 81

89 72 64 74 67 65 76 74 79 67 64 63 79 67

90 77 73 81 56 85 67 71 73 70 52 68 67 73

85 75 70 75 61 74 74 62 72 31 64 86 66 72

82 80 74 81 67 83 72 67 70 70 79 84 64 56

13.32 Rerun the analysis in Exercise 13.31 but treat both variables as fixed and crossed. Show that

the SSschool(code)in Exercise13.31 is the sum of SSschooland SSschool*codein this analysis. (Hint:

If you run this using SPSS you will have to have both sets of schools numbered 1–7.)

Discussion Questions

13.33 In the analysis of Seligman et al. (1990) data on explanatory style (Table 13.15) you will

note that there are somewhat more males than females in the Optimist group and more

females than males in the Pessimist group. Under what conditions might this affect the way

you would want to deal with unequal sample sizes, and when might you wish to ignore it?

13.34 Think of a nonstatistical example that could be used to explain to a student in an introduc-

tory statistics course why it is possible with any of the pairwise comparison tests to show

that Group 1 is not different from Group 2, Group 2 is not different from Group 3, but

Group 1 is different from Group 3.

13.35Find an example of a three-way factorial in the research literature in which at least one of

the interactions is significant and meaningful. Then create a data set that mirrors those

results.