The 3rd one is the answer
A person, typically one more remote than a grandparent, from whom one is descended:
While we make use of many varieties of data, our primary sources come
from county tabulations drawn from the U.S. censuses of population
and agriculture. We have collected those data for the decennial
population censuses from 1880 through 2000, as well as for the
agricultural censuses (which were decennial until 1920 and then more
frequent thereafter) from 1880 through 1997.3 In addition to
census-based sources, we have collected other county-level
tabulations of social characteristics. We use the population and
social indicators data to understand population structure and
change, and the agricultural census data to understand agricultural
land use. Their consistency, as well as the effectiveness and
long-term quality of the U.S. census, have made this part of our
project straightforward. Some of these data were available to us in
digital form, and others we collected in print form and then
hand-keyed into our database. All of these data are described in
Gutmann et al.
(1998). Since that document was published, we have added
data from recent censuses (1997 agriculture and 2000 population),
while maintaining their content and structure. Although our study
area is not coterminous with the 10 states, we have collected data
that covered the entire area of the 10 Great Plains states, and
often neighboring states, especially Iowa and Minnesota.
