The 2010 Census Coverage Measurement Program (CCM) conducted an independent listing of housing units in sampled block clusters called the P sample (population sample) of housing units. The P sample was then matched to the 2010 Census address list in the sampled blocks clusters, and the first ring of blocks surrounding the block clusters. The 2010 CCM classified 6,223 of 171,217 of the P-sample housing units in the United States as nonmatches to the 2010 Census address list in the sample block cluster and first ring of surrounding blocks. Of these housing units, 2,030 were classified nonmatches by CCM Estimation because they matched to a housing unit that was deleted from the final 2010 Census address list. The remaining 4,193 housing units were classified as nonmatches because they were missing from the 2010 Census address list.

As a part of the Evaluation of Address Frame and Address Quality, the 4,193 missing housing units were searched for on an expanded address list. The expanded address list included addresses within five kilometers of the sample block cluster, in addition to addresses on the Census Bureau’s Master Address File that were not in the 2010 Census such as addresses listed as businesses.

The number of missing housing units that were matched to the expanded address list is small. Of the 4,193 housing units that CCM classified as missing from the 2010 Census address list, only 150 were found during the matching to the expanded address list, 15 of which were matched to units deleted from the final 2010 Census address list (“census deletes”). Three housing units remained unresolved. The remaining 4,040 housing units persisted as nonmatches, even after expanding the address list geographically and including units not on the 2010 Census address list.

This evaluation looks at the 135 missing housing units that were found in the Evaluation of Address Frame and Address Quality matching to the expanded address list, that were not matched to census deletes. This evaluation reports the level of geography, relative to the CCM search area of the sample block cluster and first ring of surrounding blocks, at which the housing units were found. This evaluation also reports whether the missing addresses were matched to the 2010 Census address list, or to the additional addresses on the Master Address File. Finally, under some basic assumptions about the relationship between person and housing unit matching, this evaluation reports the potential impact of these two types of errors in the address list used in matching on CCM household population coverage estimates. This evaluation reports this information by addressing the following research questions.

1. The CCM search area consists of the sample block cluster plus the first ring of surrounding blocks adjacent to the block cluster. How many housing units on the final 2010 Census address list were geocoded in error to a block outside of the CCM search area?

Of the 135 missing housing units matched to the extended address list, 100 were found on the 2010 Census address list. Of these 100 housing units, 24 were located within the CCM search area, while 76 were located outside of the CCM search area but within three kilometers of the sample block cluster. These 76 housing units were geocoded in error, by the 2010 Census, to a block outside of the CCM search area. There were no units found beyond three kilometers outside of the CCM search area.

2. How many CCM P-sample housing units were correctly coded as missing from the 2010 Census address list, but found on the Census Bureau’s Master Address File?

Of the 135 missing housing units matched to the extended address list, 35 were found on the Master Address File but not the 2010 Census address list. Of these 35 units, 34 were found in the CCM search area, while only one was found outside of the search area but within one kilometer of the sample block cluster. No housing units were found beyond one kilometer but within five kilometers of the sample block cluster.

3. What is the potential impact of errors in the address list on the CCM estimates of coverage for the household population?

The potential impact of these errors in the address list on CCM estimates of coverage for the household population is low. In order to answer this question, several alternative dual system estimates for persons were computed, under the hypothetical situations where the errors in research questions (1) and (2) were corrected, under the assumption that the persons within a household would have the same outcome as the housing unit. The alternative dual system estimates showed a maximum decrease of about 8,000 persons or 0.003 percent, from the baseline dual system estimate. All of the alternative dual system estimates were less than the baseline estimate.

After the alternative dual system estimates were computed, they were used in calculations of the percent net undercount to determine how much net coverage error estimation would have been impacted by correcting for errors in the address list. The alternative percent net error estimates use the alternative dual system estimates along with a 2010 Census count that was increased in the same way as the counts and estimates used in the dual system estimate calculations. The largest increase in the percent net overcount was 0.02 percent. This measure was very robust to small changes in the dual system estimate and census count, and thus to errors in the address list used in matching.

One of the components of census coverage, the estimate of omissions, also uses the dual system estimate of the population to determine how many people were missed in the 2010 Census. The alternative omissions estimates were calculated using each alternative dual system estimate and the correct enumeration count corresponding to that estimate. The largest change in the estimate of omissions was a decrease of about 150,000 people.

Based on the evidence that refining the address list to include additional units on the Master Address File or expanding the search area geographically would result in little change to CCM estimates of coverage, we recommend no changes to the current search area or address list formation rules for CCM estimation purposes.