ing unit enumerations, as well as erroneous geographic coding of some GQs (for example, college dormitories that were assigned the geographic location of the university administrative headquarters). Additional geographic coding problems were identified by localities after release of the census counts. After August 2000, when the GQ enumeration was completed, addresses for GQs were added to the MAF, with a flag to indicate that an address was a GQ.

The GQ MAF for the 2006 ACS was constructed by merging an updated GQ inventory file, extracts from the final 2000 MAF, and a file of GQs that were closed on April 1, 2000, but may be open at other times of the year. The Census Bureau also obtained a file of federal prisons and detention centers from the U.S. Bureau of Prisons and a file of military bases and vessels from the Department of Defense. In addition, the Census Bureau conducted Internet research to identify new state prisons and state prisons that had closed. On an ongoing basis, information on new GQs and updated address information for existing GQs is collected by CAUS and the current demographic surveys listing operations.

There has been no formal evaluation of the GQ MAF for the quality of the GQ addresses or for the completeness of the list of GQs. In 2009, there will be a validation of GQ addresses in preparation for the 2010 census. It is likely that the ACS GQ population based on the current GQ MAF will differ in some respects from the 2010 census GQ population.

4-C.2
Sample Design for Group Quarters

The sampling for GQs is different from the sampling for housing units (see Hefter, 2005b). All GQ samples are selected in the main sampling phase in August preceding the data collection year. Two strata are created to sample GQs: the first stratum includes small GQs estimated to have 15 or fewer people as well as GQs listed as closed on Census Day, 2000; the second stratum includes larger GQs estimated to have more than 15 people.

For the small GQ stratum, a two-phase sample of GQs is selected, similar to how the housing unit sample is obtained. The first-phase sampling began in August 2005, when all small GQs were assigned to one of five 20 percent segments or subuniverses. One of these subuniverses is the 2006 first-stage sample, and the rest are assigned to 2007–2010. The 2006 subuniverse will not be eligible for sampling again until 2011. In August 2006, all small GQs that were new since the previous year were assigned equally to the five existing subuniverses, as will be done each August through 2009. In August 2010, the plan is to reassign the GQs in the 2006–2010 subuniverses to subuniverses for 2011–2015 and to assign new GQs likewise.

The second-phase sample of small GQs is designed to yield a 2.5 percent systematic sample of such GQs within each state, sorted by GQ type



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