A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repairs was recorded for all vehicles that were involved in accidents over a 1-year period. Those with the special bumper are the test group and the other vehicles are the control group, shown below. Each "repair incident" is defined as an invoice (which might include more than one separate type of damage). Statistic Test Group Control Group Mean Damage x¯1 = $ 1,183 x¯2 = $ 1,799 Sample Standard Deviation s1 = $ 687 s2 = $ 827 Repair Incidents n1 = 12 n2 = 9 Source: Unpublished study by Thomas W. Lauer and Floyd G. Willoughby.
