An experiment was conducted to compare the glare characteristics of four types of automobile rearview mirrors. Forty drivers were randomly selected to participate in the experiment. Each driver was exposed to the glare produced by a headlight located 30 feet behind the rear window of the experimental automobile. The driver then rated the glare produced by the rearview mirror on a scale of 1 (low) to 10 (high). Each of the four mirrors was tested by each driver; the mirrors were assigned to a driver in random order. An analysis of variance of the data produced this ANOVA table:

a. Fill in the blanks in the ANOVA table.
b. Do the data present sufficient evidence to indicate differences in the mean glare ratings of the four rearview mirrors? Calculate the approximate p-value and use it to make your decision.
c. Do the data present sufficient evidence to indicate that the level of glare perceived by the drivers varied from driver to driver? Use the p-value approach.
d. Based on the results of part b, what are the practical implications of this experiment for the manufacturers of the rearview mirrors?

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Source df SS MS F Mirrors Drivers Error Total 46.98 8.42 638.61