subcounty level by facility type for each estimate date in the time series. Second, a year-to-year change is calculated by the aggregated GQR time series of population. For some GQ types, the population estimates may be out of date, since they are basically the decennial census counts kept constant.

As the decade progresses, the census counts become increasingly outdated, and the updates, such as the GQRs collected from the states, cannot always be counted on, which affects the quality of the population estimates. Following the release of counts from the decennial census, the Census Bureau typically conducts a formal evaluation of errors (bias and precision) in its population estimates for various levels of geography. These tests generally treat the census counts as the gold standard against which the population estimates are evaluated. The Census Bureau recently proposed a project to evaluate the 2010 round of population estimates against the 2010 census counts and awarded eight contracts to external researchers to evaluate alternative population estimation methodologies.

The purpose of this program will be to evaluate the current method by comparing the population estimates of the total resident population and the household population at the national, state, and county levels with the census counts. The plan is to examine the national, state, and county population estimates by selected characteristics (e.g., age, sex, race, Hispanic origin). At the subcounty level the plan will be to evaluate both the subcounty population totals and the housing unit estimates. Population estimates developed using the housing unit method at the national, state, county, and subcounty levels will also be evaluated. The population estimates produced using a housing unit method will be for the total resident population and the household population; they will not include any demographic characteristics data, nor will they provide information about the GQ population.

Despite uncertainty surrounding the quality of the GQ estimates prepared by the PEP, the proposed evaluation research, as planned, will focus only on estimated population (household and GQ populations combined), and household population compared with total 2010 census counts. The Census Bureau plans to consider the GQ estimates separately at a later time, but this could be a missed opportunity to better understand the challenges surrounding the GQ population estimates in relation to the total population estimates and to inform the deliberations about the role of the GQ populations in the ACS. The panel thinks that an evaluation of the GQ estimates should be conducted along with the evaluation of other aspects of the population estimates program.

Recommendation 4-1: The Census Bureau should consider amending its current plan for evaluating the 2010 population estimates against the 2010 census counts to include an evaluation of the 2010 estimates of the GQ population at all levels of geography for which such estimates are prepared. This research should identify estimated bias and imprecision by GQ type. The evaluation of the 2010 population estimates should also be viewed as an opportunity to foster a closer collaboration between the Population Estimates Program and the ACS office to ensure that the estimates meet the needs of all users.

As discussed, currently the population controls for GQ estimates in the ACS products are applied at the state level, and this topic needs to be considered in the context of their effect on the mean square errors as well, given that inaccurate population controls will be more likely to introduce error than to reduce it. While there are arguments for considering county, or even



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