A study was recently conducted by the Bonneville Power Association (BPA) to determine attitudes regarding the association’s policies in western U.S. states. One part of the study asked respondents to rate the performance of the BPA on its responsiveness to environmental issues.

The following responses were obtained for a sample of 12 urban residents and 10 rural residents. The ratings are on a 1 to 100 scale, with 100 being perfect.

Urban Rural 76 55 90 80 86 94 60 40 43 85 96 92 50 77 20 68 30 35 82 59 75 84

a. Based on the sample data, should the BPA conclude that there is no difference between the urban and rural residents with respect to median environmental rating? Test using a significance level of 0.02.

b. Perform the appropriate parametric statistical test and indicate the assumptions necessary to use this test that were not required by the Mann–Whitney tests. Use a significance level of 0.02. (Refer to Chapter 10, if needed.)