Under the estimating methods used in the CPS, all of the results for a given month become available simultaneously and are based on returns for the entire panel of respondents. The CPS estimation procedure involves weighting the data from each sample person. The base weight, which is the inverse of the probability of the person being in the sample, is a rough measure of the number of actual persons that the sample person represents. Almost all sample persons in the same state have the same base weight, but the weights across states are different. Selection probabilities may also differ for some sample areas due to field subsampling, which is done when areas selected for the sample contain many more households than expected. The base weights are then adjusted for noninterview, and the ratio estimation procedure is applied.
a. First-stage ratio estimate. The purpose of the first-stage ratio adjustment is to reduce the contribution to variance that results from selecting a sample of PSUs rather than drawing sample households from every PSU in the nation. This adjustment is made to the CPS weights in two race cells: black and nonblack; it is applied only to PSUs that are nonself-representing and for those states that have a substantial number of black households. The procedure corrects for differences that existed in each state cell at the time of the 2010 census between 1) the race distribution of the population in sample PSUs and 2) the race distribution of all PSUs (both 1 and 2 exclude self-representing PSUs).
b. Second-stage ratio estimate. This procedure substantially reduces the variability of estimates and corrects, to some extent, for CPS undercoverage. The CPS sample weights are adjusted to ensure that sample-based estimates of population match independent population controls. Three sets of controls are used:
1) 51 state controls of the civilian noninstitutional population 16 years of age and older.
2) national civilian noninstitutional population controls for 14 hispanic and 5 nonhispanic age-sex categories.
3) national civilian noninstitutional population controls for 66 white, 42 black, and 10 "other" age-sex categories.
The independent population controls are prepared by projecting forward the resident population as enumerated on April 1, 2010. The projections are derived by updating demographic census data with information from a variety of other data sources that account for births, deaths, and net migration. Estimated numbers of resident Armed Forces personnel and institutionalized persons reduce the resident population to the civilian noninstitutional population. Estimates of net census undercount, determined from the Post Enumeration Survey, are added to the population projections. Prior to January 2013, the projections were based on earlier censuses, and prior to January 1994, there was no correction for census undercount. A summary of the current procedures used to make population projections is given in “Revisions in the Current Population Survey Effective January 2003" in the January 2003 issue of Employment and Earnings.