Income and road rage. The phenomenon of road rage has received much media attention in recent years.

Is a driver’s propensity to engage in road rage related to his/her income? Researchers at Mississippi State University attempted to answer this question by conducting a survey of a representative sample of over 1,000 U.S. adult drivers (Accident Analysis and Prevention, Vol. 34, 2002). Based on how often each driver engaged in certain road rage behaviors (e.g., making obscene gestures at, tailgating, and thinking about physically hurting another driver), a road rage LO4 score was assigned. (Higher scores indicate a greater pattern of road rage behavior.) The drivers were also grouped by annual income: under $30,000, between

$30,000 and $60,000, and over $60,000. The data were subjected to an analysis of variance, with the results summarized in the next table.

Income Group Sample Size Mean Road Rage Score Under $30,000 379 4.60 $30,000 to $60,000 392 5.08 Over $60,000 267 5.15 ANOVA results: F@value = 3.90 p@value 6 .01

a. Is a driver’s propensity to engage in road rage related to his/her income?

b. An experimentwise error rate of .01 was used to rank the three means. Give a practical interpretation of this error rate.

c. How many pairwise comparisons are necessary to compare the three means? List them.

d. A multiple-comparisons procedure revealed that the means for the two income groups Between $30 and $60 thousand and Over $60 thousand were not significantly different. All other pairs of means were found to be significantly different. Summarize these results in tabular form.

e. Which of the comparisons of part c will yield a confidence interval that does not contain 0?