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Using the American Community Survey: Benefits and Challenges
for that month, in order to make all the data for each monthly sample relate to the same time period. The units resolved in a given tabulation month comprise the mail, CATI, and CAPI responses received in that month and also the units determined in that month to be final nonresponding households, vacant housing units, and ineligible units. This procedure can be viewed as a form of nonresponse “replacement procedure” (Kish and Hess, 1959), in which sampled units resolved in the given month that were selected for prior months are treated as replacements for units selected for the given month that were resolved in later months.
Given this definition of the monthly samples, all the data used for analysis for a 1-year or multiyear period are collected during the specified calendar year or years. (An attraction of using tabulation months is that data collection is completed at the end of the year; if the monthly samples were defined in terms of sample months, it would be necessary to wait until the following February before all the data were collected for a given year.) Survey sampling weighting methods are applied to the respondents for the given period in order that valid estimates can be produced. These methods include weights to compensate for unequal selection probabilities, weighting adjustments for nonresponse, and calibration adjustments that compensate for noncoverage and can improve the precision of some survey estimates. Separate sets of weights are developed for person-level and housing unit-level analyses.
The Census Bureau has developed a nine-step weighting process for each 1-year data file, as summarized in Box 5-1. This box and the chapter text apply only to the weighting process for the housing unit population; see Box 5-2 for a brief description of the weighting process for the group quarters population.
Step 1 in Box 5-1 is the standard inverse selection probability weighting: if, say, a housing unit is selected with a probability of 1 in 10, the unit is assigned a base weight of 10, since it represents 10 housing units in the population. Subsequent steps adjust the base weights to compensate for deficiencies in the sample and to improve the precision of some estimates. These adjustments are performed within “estimation areas,” which are single larger counties or combinations of smaller counties (the nonresponse adjustments in step 3 are carried out at the tract level; see below).
Steps 1 to 5 are adjustments made to the housing unit weights. The weights resulting from steps 1 to 5 apply to the household and all persons in it. Step 6 is an adjustment that is applied at the person level, leading to different weights for persons in the same household, and a revised household weight is developed in step 7. The last two steps are final adjustments to the weights.
Section 5-B describes these nine steps in more detail, and Sections 5-C and 5-D examine steps 5 and 6 more carefully. The calibration of the