Refer to the Environmental Science & Technology study of sorption of organic vapors, Exercise 12.7. Consider modeling the vapor retention coefficient y as a function of one of the two quantitative variables, temperature (x₁) and relative humidity (x₂).

a. Propose a model that hypothesizes a curvilinear relationship between mean retention E(y) and relative humidity x₂. Draw a sketch of the model.

b. Propose a model that hypothesizes a third-order relationship between mean retention E(y) and temperature x₁. Draw a sketch of the model.

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.