To estimate the population totals for the poststratification
cells, the NAEP sampling and weighting contractor obtained two
sources of information: Census projections for population totals
by age, race, and sex, for October of 2000. These figures were
obtained from the Census website. Detailed cross tabulations by
age, race, grade, and Census region. These tabulations were
obtained from the Census website from the October Current
Population Survey (CPS) Educational Supplement for October 1998
and 1999. To estimate the size of a given cohort, NAEP
statisticians refined the Census projections using CPS data on
percent in school, percent in each race/ethnicity by age, by
grade category, and so forth. The four race/ethnicity groupings
used in poststratification are as follows: other non-Hispanic,1
and Within each of these four categories, Westat produced
aggregations for the following age groups: age 9 and not age 9,
age 13 and not age 13, and age 17 or younger2 . In this process,
Census totals were written as Xi