There are two obvious ways in which the census count for an individual can be in error: A person could be included in the census as an enumeration when he or she should have been omitted—an overcount—or the person could be omitted from the census when she or he should have been included—an undercount. In addition, since the primary applications of census counts are for apportionment of the states and redrawing of congressional districts, it is important that each individual be counted in their appropriate location. When a person is counted in other than the correct location, the effect of this error depends on both the distance between the recorded location and the true location and on the intended application of the counts (see below).
Given that, we decided in this report to separately categorize undercounts from overcounts, which are always errors regardless of the location of the enumeration, and those from enumeration errors that result from counts in the wrong location. This approach is not due to any sense that the latter errors are less important, but that they have different causes and therefore different solutions, and second that they are of different types as a result of the various degrees of displacement.
This classification of census coverage error differs from the classification that has been typical up now. In that classification scheme, an overcount was any erroneously included enumeration, which included enumerations that were in the wrong location, regardless of whether the error was a few blocks or hundreds of miles. Similarly, an undercount was any erroneously omitted enumeration, which included enumerations that were in the census but were attributed to another (incorrect) location. As a result, in the previous scheme, an enumeration in the wrong location was represented as two errors: an overcount for the location that was recorded and an undercount at the correct location. The approach adopted here for classifying coverage error is consistent with a framework developed by Mulry and Kostanich (2006), which is described in Chapter 5. We now provide more detail on the nature and causes of these various types of census coverage error.
Omissions result from a missed address on the decennial census’ Master Address File (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, or people missed due to having no usual residence.