358 Chapter 11 Simple Analysis of Variance
Exhibit 11.4 JMP analysis of data in Exercise 11.8Tests that the Variances are Equal
Mean. Abs Dif Mean. Abs Dif
Level Count Std Dev to Mean to Median
PE 10 11.11755 9.600000 9.600000
SC 11 7.13379 5.537190 5.636364
SIT 14 3.95094 3.071429 3.071429
WL 10 7.10634 6.100000 6.100000
Test F Ratio DF Num DF Den Prob > F
O’Brien [.5] 5.1694 3 41 0.0040
Brown-Forsythe 6.3543 3 41 0.0012
Levene 6.6330 3 41 0.0009
Bartlett 3.5390 3 * 0.0140
Welch Anova testing Means Equal, allowing Std’s Not Equal
F Ratio DF Num DF Den Prob > F
5.3749 3 19.128 0.007511.12 The following results, also produced by JMP, include tests for heterogeneity of variance and
Welch’s modification to allow for heterogeneity of variance. How does this result compare
to your answer to Exercise 11.8b? From what you know from this chapter and from Chapter 7,
what are the Fratios in the middle table?