Chicago has installed cameras at various intersections throughout the city. The cameras photograph the license plate of any car engaging in a moving violation (such as driving through a red light or failing to stop completely prior to turning on red). Researchers with the city wanted to know whether there is a difference between the number of violations on Wednesdays and Saturdays. They randomly selected 30 cameras on a Wednesday and Saturday of the same week. The following data represent the number of violations recorded.

(a) Why does it make sense to pair by the camera?
(b) Determine the difference in the data as “Sat–Wed.” raw a boxplot of the differenced data. Explain why a large sample size is needed to analyze this data using Student’s t-distribution.
(c) Does the sample evidence suggest there is a difference in the number of violations on a Wednesday versus Saturday?
(d) Can you think of any variables that may confound the results of the study?

Transcribed Image Text:

Camera ID 2244 1671 2081 1964 1743 1151 2321 1142 1652 1514 2054 1934 1234 3082 2672 Sat Wed 2 19 14 6 10 3 5 4 1 11 30 3 3 3 6 7 1 12 6 26 2 4 8 11 17 24 9 3 4 3 Camera ID 1031 2412 2013 1612 1142 1982 2023 2523 1011 1502 2154 1274 1282 1123 1721 Sat 3 9 13. 7 2 24 5 2 5 1 13 2 5 Wed 3 1 0 5 47 2 2 16 3 4 1 0 2 2 3 19 40