The data in the "rent.dat" dataset were collected to study the variation
in rept paid in 1977 for agricultural land planted in alfalfa.  The
variables are:

       average rent per acre planted to alfalfa
       average rent paid for all tillable land
       density of dairy cowes (number per square mile)
       proportion of farm land used as pasture
       1 if liming is required to grow alfalfa; 0 otherwise

The unit of analysis is a county in Minnesota.  The 67 counties with
appreciable rented farmland are included.

Alfalfa is a high protein crop that is suitable feed for dairy cows.  It
is thought that rent for land planted to alfalfa relative to rent for
other agricultural purposes would be higher in areas with a high density of
dairy cows, and rents would be lower in counties where liming is required.