A group of high-risk automobile drivers (with three moving violations in one year) are required, according to random assignment, either to attend a traf?c school or to perform supervised volunteer work. During the sub-sequent ?ve-year period, these same drivers were cited for the following number of moving violations:

NUMBER OF MOVING VIOLATIONS TRAFFIC SCHOOL VOLUNTEER WORK 26 15 14 23 10

(a) Why might the Mann-Whitney U test be preferred to the t test for these data?
(b) Use U to test the null hypothesis at the .05 level of signi?cance.
(c) Specify the approximate p -value for this test result.