Data set: Tires
The data file Tires relates to five brands of tires chosen at random from local stores. Six tires of each brand were selected and placed in random order on a machine that tested tread durability in thousands of miles.
a. Graph the data and compare the center and spread of the durability measurements for each group (Brand of tire). Does any group have outliers or skewed data?
b. Conduct an ANOVA. Does the ANOVA show a significant difference exists between group means?
c. Create residual plots and compare the group standard deviations. Are the model assumptions satisfied?
d. Brand is used simply to identify different brands within the study. Explain why a simple linear regression model should not be used for the data, even though Brand could be treated as a quantitative variable.