Question: Chemical composition of rain water. The Journal of Agricultural, Biological, and Environmental Statistics (March 2005) presented a study of the chemical composition of rain water. The nitrate concentration, y (milligrams per liter), in a rain water sample was modeled as a function of two independent variables: water source (groundwater, subsurface flow, or overground flow) and silica concentration (milligrams per liter). Identify the type (quantitative or qualitative) for each independent variable.