data uspop;
  * From Fox, Applied Regression Analysis.  ;
  * Population of the United States ;
  * Source of Data: Statistical Abstract of the United States: 1994, ;
  * Washington, DC: U.S. Bureau of the Census. ;
  input year pop ;
  * year "year" ;
  * pop "Population in Millions" ;
cards;
1790	3.929
1800	5.308
1810	7.240
1820	9.638
1830   12.866
1840   17.069
1850   23.192
1860   31.443
1870   39.818
1880   50.156
1890   62.948
1900   75.995
1910   91.972
1920  105.711
1930  122.775
1940  131.669
1950  150.697
1960  179.323
1970  203.302
1980  226.542
1990  248.710
;
run;

proc means;
run;