These data are estimates of the resident population of the counties in the United States, by single year of age (0, 1, 2, ..., 84, 85 and over), sex (male, female), race (White; Black; American Indian and Alaska Native; Asian and Pacific Islander) for July 1 of each year from 1990 to 1999.  In the discussion below, these data are referred to as the county detail estimates.

The county estimates included in this release are developed in a two-step procedure.  First a set of state estimates by age, sex, race, and Hispanic origin (with the same categories as given above) are developed.  These state estimates are developed using a cohort-component technique.  A complete description of that methodology is included as Appendix A.  The county detail estimates are produced in the second step using a ratio method.  The ratio method is a mathematical technique for adjusting data to sum to a pre-determined total.  It consists of multiplying each element of the data by the ratio formed by dividing the desired total by the sum of the data.  When there are multiple totals to which we wish to adjust our data, as with the county estimates, we first  partition the data into groups which correspond to the desired totals, then construct and apply ratios for each group using the same method as in the single-total situation.  Applying the ratio method to a data set is referred to as raking.