Chemical composition of rain water. Researchers at the University of Aberdeen (Scotland) devel- oped a statistical model for estimating the chemical composition of water (Journal of Agricultural, Bio- logical, and Environmental Statistics, March 2005). For one application, the nitrate concentration y (milligrams per liter) in a water sample collected after a heavy rainfall was modeled as a function of water source (groundwater, subsurface ?ow, or overground ?ow).
(a) Write a model for E(y) as a function of the qualitative independent variable.
(b) Give an interpretation of each of the β parameters in the model, part c.