An experimental bumper was designed to reduce damage in low-speed collisions. This bum- per was installed on an experimental group of vans in a large eet, but not on a control group. At the end of a trial period, there were 12 repair incidents (a "repair incident" is an accident that resulted in a repair invoice) for the experimental group and 9 repair incidents for the control group. The dollar cost per repair incident is shown below.
(a) Use Mega- Stat or MINITAB to perform a two-tailed Wilcoxon rank sum test (Mann-Whitney test) at 5 .05.
(b) Perform a two-tailed parametric t test for two independent sample means by using Excel or MegaStat. Do you get the same decision? (Data are from Floyd G. Willoughby and Thomas W. Lauer, confidential case study.)

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