counties selected with probability proportional to 1992 population
statepop
state abbreviation
county
land area of country, 1990 (square miles)
population of county, 1992
number of physicians, 1990
farm population, 1990
number of farms, 1987
number of acres devoted to farming, 1987
number of veterans, 1990
percent of veterans from Vietnam era, 1990
Lohr (1999). Sampling: Design and Analysis, Duxbury, p. 190 -- 192 and 444.