SECOND EPISODE (PROBLEM 2): Thomas wants to compare the mean concentration of carbon monoxide (CO) on residential versus commercial streets, since these differ in terms of car traffic. In each of three neighborhoods of Montral (named A, B, and C below), he randomly chooses four locations for each type of street, for a total of 24 observations (2 street types x 3 neighborhoods x 4 locations). At each location, he measures CO concentration in the air over a period of 10 hours (8:00 AM-6:00 PM), and obtains the following data (in ppm/h). C Residential 0.9 Type of street A 1.0, 1.2, 0.9, 0.5 (0.9) 1.6, 2.1, 2.5, 2.2 (2.1) 1.5 Neighborhood B 0.4, 0.8, 0.6, 0.2 (0.5) 0.8, 1.4, 1.0, 1.2 (1.1) 0.8 Commercial 1.1, 1.4, 1.5, 1.2 (1.3) 3.0, 2.5, 3.2, 3.7 (3.1) 2.2 2.1 X = 1.5 j. 10-a) Draw a graph that gives insight into the possible presence of an interaction between the two classification factors. Do you suspect the presence of an interaction? Explain why. 15 Thomas has prepared a part of the ANOVA table. df SS MS 2 7.84 3.92 Source of variation Type of street Neighborhood Type of street-by- Neighborhood Error Total 23 19.84 10-b) Test whether or not the difference between residential and commercial streets in mean atmospheric CO concentration is the same among the three neighborhoods, and whether or not CO concentration in the air is the same, on average, for the two types of streets. Note that Neighborhood is considered a random block factor in the ANOVA. Use a = 0.05. /16