A group of high-risk automobile drivers (with three moving violations in one year) are required, according to random assignment, either to attend a traffic school or to perform supervised volunteer work. During the sub-sequent five- year period, these same drivers were cited for the following number of moving violations:
NUMBER OF MOVING VIOLATIONS
TRAFFIC SCHOOL VOLUNTEER WORK
0.............. 26
0............... 7
15............. 4
9............... 1
7............... 1
0............. 14
2............... 6
23.............. 10
7
8
(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 significance.
(c) Specify the approximate p - value for this test result.