producing counts that are as accurate as possible when aggregated to various levels of geography.)

People who were not included in the list of census enumerations but should have been are census omissions. Omissions can result from a missed address on the MAF, a missed housing unit in a multiunit residence in which other residences were enumerated, a missed individual in a household with other enumerated people, and people with no residence.

In addition to omissions, erroneous enumerations, and duplications, enumerations in the wrong location can also affect the accuracy of census counts. A count in the wrong location can result from (1) a misunderstanding of the census residence rules and the resulting reporting of someone in the wrong residence—for example, having an enumerator assign someone to the wrong choice from among several part-time residences, and (2) placing an address in the wrong census geographic location (called a geocoding error).

Furthermore, demographic errors, which occur when a person’s demographic characteristics are incorrectly reported or assigned and which can also result from an improper imputation of an individual’s demographic characteristics, can add error to census counts. For example, if someone’s age is misreported on the census form, this adds one tally in error to the count for one age group and subtracts one tally in error for another. However, this does not impact census counts that are not disaggregated by age group.

Erroneous enumerations and omissions contribute to errors in census counts for any geographic aggregate that includes the addresses of the persons involved with those errors. Whether or not errors in geographic or demographic characteristics result in errors in census counts depends on the level of demographic and geographic aggregation for which the census counts are used. The more detailed the geographic and demographic domain of interest, the greater the chance that errors in geographic and demographic detail will affect the quality of the associated counts. For example, placing a person in the wrong census tract but in the right county is not an error for census applications except when one uses census counts below the county level. However, placing someone in the wrong state affects most uses of census counts. Similarly, attributing someone to the wrong age group does not affect overall population counts at any level of geographic aggregation, but it will result in an error for counts by age group.

As touched on above, errors in census counts can result from missing information and the resulting use of imputation for item and unit nonresponse. For example, missing information on the total number of residents in a housing unit can result in imputation of this number, which can add to errors in census counts of the total population for areas containing that housing unit. As described in National Research Council (2004b: 128, Box 4.2) the 2000 census used item imputation, whole-person imputation, and four types of whole-household imputation to complete responses with missing information. The procedure used depended on which persons in a household were and were not census

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