Researchers at General Motors collected data on 60 U. S. Standard Metropolitan Statistical Areas (SMSA's) in a study of whether or not air pollution contributes to mortality. The data are available as [smsa. csv](smsa. csv) on the course web page. The dependent variable for analysis is age adjusted `Mortality` rate. Several (potential) explanatory variables include measures of demographic characteristics of the cities, of climate characteristics and the air pollution potential of three different chemicals. Specifically: