In addition, the use of adjustment is complicated since for some important applications one needs adjusted counts at low levels of demographic and geographic aggregation, and a sample survey, by design, is intended to make estimates at more aggregate levels. A decision whether to use adjusted counts for any purpose must therefore rest on an assessment of the relative accuracy of the adjusted counts compared with the census counts at the needed level of geographic or demographic aggregation. One key issue that depends on the application is whether to base this assessment on population shares or population magnitudes. The Census Bureau’s decision not to adjust the redistricting data for the 2010 census, due for release by April 1, 2011, was based on the difficulty of making this assessment within the required time frame.
Although it is important to assess census coverage, it would also be extremely helpful to use that assessment to improve the quality of subsequent censuses. Consequently, an important use of coverage measurement is to help to identify important sources of census coverage errors and possibly to suggest alternative processes to reduce the frequency of those errors in the future. Although drawing a link between census coverage errors and deficient census processes is a challenging task, the Census Bureau thinks that substantial progress can be made in this direction. Therefore, the 2010 coverage measurement program has the goal of identifying the sources of frequent coverage error in the census counts. This information can then be used to allocate resources toward developing alternative census designs and processes that will provide counts with higher quality in 2020. It is conceivable that use of such a feedback loop could also provide substantial savings in census costs, in addition to improvement in census quality because the tradeoff between the effect on accuracy and on census process costs might now be better understood. The panel fully supports this modification of the objectives of coverage measurement in 2010.
To see the value of this shift in the objective of coverage measurement, consider, for example, the findings from demographic analysis for the 2000 census, which showed that there was a substantial undercount of young children relative to older children. Specifically, Table 2-1 shows the net undercount rates—(DSE – C)/DSE, where DSE indicates the adjusted count, and C indicates the corresponding census count)—by demographic group in 2000 on the basis of the revised demographic analysis estimates (March 2001) (see National Research Council, 2004b:Chapter 6): One hypothesis is that the undercoverage for children aged 10 and under was at least in part due to the imputation of age for those left off the census