Sampling for Nonresponse Follow-Up

The panel has concluded that a properly designed and well-executed sampling plan for field follow-up of census mail nonrespondents will save over $100 million (assuming an overall sampling rate of 75 percent). Furthermore, sampling for nonresponse follow-up will reduce the Census Bureau's total workload, which will permit improvements in the control and management of field operations, and will allow more complete follow-up of difficult cases that could lead to an increase in the quality of the census data collected by enumerators. In addition, nonresponse follow-up interviews could be completed in a more timely fashion, which would lead to improvements in quality when the planned integrated coverage measurement operation is used.

Of course, sampling for nonresponse follow-up will add sampling variability to census counts. However, imprecision in the census counts at low levels of geographic aggregation due to added variance through use of sampling for nonresponse follow-up will not cause any systematic biases, because under sampling for nonresponse follow-up only characteristics of people found in a tract contribute to the estimates for that tract. Furthermore, the relative amount of variance due to sampling decreases as the population of an area increases, and the amount of sampling variance can be measured statistically. As a result of this, and also due to the possibly higher quality of collected data resulting from the use of sampling, the panel believes that sampling for nonresponse follow-up will provide data of equal or better quality when used for congressional apportionment and that it will approximately replicate, at lower levels of aggregation, what would be obtained with 100 percent follow-up.

The panel further concludes that the prespecified nature of the sampling design for nonresponse follow-up and the fact that enumerators will not know whether households they are not visiting are mail respondents or nonrespondents that are not sampled ensures that sampling does not present a new opportunity for manipulation of census counts by enumerators.

Adjusting for Differential Undercoverage

Because the master address list is incomplete, because households are sometimes missed in listed housing units, and because individuals who live in otherwise enumerated households are at times missed, there is (gross) undercoverage in the decennial census. At the same time, people can be enumerated in multiple ways, possibly at several residences, so there is also (gross) overcoverage in the decennial census. The difference between undercoverage and overcoverage is referred to as net under-



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