Refer to the Accident Analysis and Prevention (Vol. 34, 2002) study of road rage, Exercise 9.27 (p. 509). Recall that the mean road rage scores of drivers in the three income groups, under $30,000, between $30,000 and $60,000, and over $60,000, were 4.60, 5.08, and 5.15, respectively.
a. An experiment-wise error rate of .01 was used to rank the three means. Give a practical interpretation of this error rate.
b. How many pairwise comparisons are necessary to compare the three means? List them.
c. A multiple comparisons procedure revealed that the means for the income groups $30,000-$60,000 and over $60,000 were not significantly different. All other pairs of means were found to be significantly different. Summarize these results in table form. d. Which of the comparisons of part b will yield a confidence interval that does not contain 0?