In the 1960's and 1970's, the United States began to monitor urban air pollution as 
concerns arose over the effect of pollution on the cities' inhabitants as well as on 
geographically distant areas through acid rain, for example. The data set under 
consideration contains the following variables (in this order):

 -- region of the United States (defined below)
 -- average annual SO2 content of the air in micrograms per cubic meter
 -- average annual temperature in degrees Fahrenheit
 -- number of manufacturing enterprises employing 20 or more workers
 -- population size from the 1970 census, in thousands
 -- average annual wind speed in miles per hour
 -- average annual precipitation in inches
 -- average numbers of days with precipitation per year

for each of 41 cities. The data were obtained from various government agencies. Those 
variables described as ``averages'' are averages of the 1970, 1971, and 1972 values, 
when available.