Refer to the Environmental Science & Technology study of sorption of organic vapors, Exercise 12.7. Consider using the qualitative variable, organic compound, as a predictor of the retention coefficient y. Recall that five organic compounds were studied: benzene, toluene, chloroform, methanol, and anisole.

a. Write a model for E(y) as a function of organic compound at two levels.

b. Interpret the β parameters in the model.

c. Explain how to test for differences among the mean retention coefficients of the five organic compounds.

Data from Exercise 12.7

Environmental Science & Technology (Oct. 1993) published an article that investigated the variables that affect the sorption of organic vapors on clay minerals. The independent variables and levels considered in the study are listed here. Identify the type (quantitative or qualitative) of each.