Refer to the June 2007 Virginia Department of Transportation (VDOT) study of a newly adopted photo-red-light enforcement program, Exercise. Recall that the VDOT provided crash data both before and after installation of red light cameras at several intersections. The data (measured as the number of crashes caused by red light running per intersection per year) for 13 intersections in Fairfax County, Virginia, are reproduced in the next table and saved in the REDLIGHT file. The VDOT wants to determine if the photo-red enforcement program is effective in reducing red-light-running crash incidents at intersections. Use the nonparametric Wilcoxon singed rank test (and the accompanying MINITAB printout below) to analyze the data for the VDOT.

Based on Virginia Transportation Research Council, "Research Report: The Impact of Red Light Cameras (Photo-Red Enforcement) on Crashes in Virginia," June 2007.

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Wilcoxon Signed Rank Test: Difference Test of median = 0.000000 versus median > 0.000000 N for Wicoxon Ξ9timated Median Difference 13 13 79.0 0.011 0.s Data for Exercise 14.44 Intersection Before Camera After Camera 3.60 0.27 0.29 4.55 2.60 2.29 2.40 0.73 3.15 3.21 0.88 1.35 7.35 1.36 1.79 2.04 3.14 2.72 0.24 1.57 0.43 0.28 1.09 4.92 10 12 13