The sampling frame for the ACS is based on the Census Bureau’s Master Address File (MAF), which is an inventory of addresses in the United States, including housing units and group quarters. However, the procedures developed to maintain and update the MAF are focused on housing units and are less adequate for group quarters, a situation that affects the representativeness of the sampling frame and increases data collection costs because of the additional work necessary to clean and improve the sample.
The Census Bureau should explore opportunities for developing and maintaining a better inventory of group quarters, and possibly reducing the amount of work that is invested in updating cases after they have been assigned to a field representative. For example, the ACS office could take advantage of the successful partnerships already in place between other Census Bureau divisions and state demographic offices and other local entities. These relationships could be expanded to better meet ACS sampling frame needs. Collaborations with other federal statistical agencies and organizations that also collect data about residents of various group quarters could be explored as a source of updates to the sampling frame.
The current ACS sample design is suitable for producing estimates of the characteristics of the household population for small-area geographies, but it is not optimized for substate estimates of the GQ population. Even though the Census Bureau does not intend to release detailed characteristics of GQ residents for small geographic areas, GQ data are included in the total population estimates. The Census Bureau should evaluate the current sample allocation rates at the state and substate levels, as well as the subsampling rates in large group quarters, to determine whether there are opportunities for a more efficient design.
Similar to problems with the sample design, the current group quarters weighting and estimation procedures for group quarters populations are not optimized for small-area estimates. The ACS substate samples are highly variable, particularly by GQ type, and some geographic entities with known GQ facilities have none represented in the sample. If the sample for a smaller area does not include group quarters, the state-level nonresponse adjustment factors and population controls will disproportionately increase the weights of group quarters in other areas. When the 5-year data are released for smallareas, in many cases the estimates will not reflect local reality. The Census Bureau should:
Conduct an evaluation to better understand the quality of the estimates affected by group quarters and the effects of the population controls on these estimates.
Evaluate alternative approaches for producing estimates for areas in which the quality of the direct estimates is in question.
Clearly label data tables and other data products that may be affected by the presence of group quarters in a geographic area.