Counting People in the Information Age (1994) / Chapter Skim
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4 Sampling and Statistical Education
4 Sampling and Statistical Education
Pages 96-135
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From page 96... ...
. Data from housing units sampled for nonresponse follow-up would allow estimation of counts and characteristics of mailback nonrespondents who are not sampled.
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From page 97... ...
Although the survey identified a net undercount of about 1.6 percent and substantial differential undercount by geography and demographic characteristics, the official 1990 census counts did not use the information obtained as part of the PES. During the 1995 census test, the Census Bureau plans to evaluate a new integrated coverage measurement method, CensusPlus, designed to run concurrently with the main census operations and thereby to facilitate production of official counts by the legal deadlines.
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From page 98... ...
In turn, NRFU operations pushed back the beginning of coverage measurement by the Post-Enumeration Survey. The long delay between Census Day and the beginning of coverage measurement compromised the ability of the PES to operate accurately and was one of several factors making it impossible for the Census Bureau to incorporate the PES results into official counts released by the legal deadlines.
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From page 99... ...
As a result, truncation would have greatly increased the differential undercount in the census enumeration, placing further burden on integrated coverage measurement. Plans for the 1995 Census Test On the basis of these conclusions, the Census Bureau decided to focus on evaluating sampling for NRFU in the 1995 census test.
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From page 100... ...
A major purpose of testing sampling for NRFU in the 1995 census test is to learn more about the relative merits of sampling individual housing units (a unit sample) versus whole blocks (a block sample)
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From page 101... ...
It is also conceivable that Census Bureau staff might be less committed to their enumeration efforts in the belief that sampling will take care of nonresponse. Unfortunately, there is no way to learn from census tests whether concerns about such reactions are warranted.
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From page 102... ...
about responding units in that block and in blocks judged similar in terms of geography and demographic characteristics. There is reason to expect that a unit sample would generally produce more accurate estimates than a block sample of the same size, because there is probably some within-block correlation in household size and other attributes of mailback nonresponse housing units, even within carefully selected strata.
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From page 103... ...
A related consideration is whether the choice of sampling design affects coverage in NRFU housing units. For example, with the more concentrated effort involved in following up a block sample, enumerators might be more likely to discover housing units that had been omitted from the frame (e.g., garage apartments)
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From page 104... ...
Inevitably, mail returns will continue to trickle in after selection of the NRFU sample. Because these returns will not come from a random sample of all housing units that failed to respond prior to sampling, use of data from these returns could bias estimates.
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From page 105... ...
INTEGRATED COVERAGE MEASUREMENT In addition to the use of sampling and estimation for nonresponse follow-up as described above, current census design plans call for a separate data collection effort in a smaller sample of blocks to measure the coverage of all census operations that precede it. The preceding census operations include address list development, mailout-mailback of census questionnaires, special enumeration methods, and nonresponse follow-up.
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From page 106... ...
Dual-system estimation as used in recent censuses is based on data collected for a stratified sample of households in a coverage measurement survey. (DSE more broadly construed has taken many forms in problems of human and animal population estimation see e.g., Marks et al., 1974; Seber, 1982; Chandrasekhar and Deming, 1949~.
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From page 107... ...
Therefore, the need for coverage measurement in 2000 promises to be at least as great as in previous censuses. Current plans for the 2000 census are predicated on the use of integrated coverage measurement as an essential part of census-taking and not just as an evaluation of other census operations, although ICM would also produce valuable evaluative data.
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From page 108... ...
Finally, it should be possible to garner wide support for a one-number census based in part on ICM given the overriding importance of reducing census cost and reducing differential undercount. Recommendation 4.2: Differential undercount cannot be reduced to acceptable levels at acceptable costs without the use of integrated coverage measurement and the statistical methods associated with it.
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From page 109... ...
In practice, this means that the ICM method chosen must be thoroughly evaluated prior to going into the field in 2000. Alternative Methods for Integrated Coverage Measurement Since 1990 three basic designs for integrated coverage measurement have received serious attention: (1)
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From page 110... ...
The extensive program of research evaluating the 1990 PES methodology, including criticisms of that methodology, has played an important role in developing plans for integrated coverage measurement for the 2000 census. We believe that, with modifications, DSE based on a PES could be used in the 2000 census, satisfying the above criteria, if other methods are judged to be unreliable or infeasible.
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From page 111... ...
Current plans call for a sample of 100 to 200 ICM sample blocks at each of the four 1995 census test sites. Early in the year, prior to the census mailout, interviewers will canvass the ICM sample blocks to construct an independent listing of housing units (and addresses)
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From page 112... ...
Conversely, ICM interviewers may determine that some households enumerated by mailback or NRFU were erroneously enumerated and should be removed from the roster. The end product of these operations is a corrected or resolved roster of both housing units and people in the ICM sample blocks, from which resolved counts of units and of people by age, sex, race, and other variables would be calculated.
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From page 113... ...
Control of these simultaneous operations is predicated on improved management capabilities and, in particular, on very good control of addresses using the TIGER geographical information system (see Chapter 2) in order to separate distinct operations that may be going on at the same time in adjacent housing units.
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From page 114... ...
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From page 115... ...
· The precensus canvass for housing units conducted in ICM blocks may affect awareness of the census and consequently response to the regular census in those blocks particularly if census personnel knock on doors to verify the existence of housing units. · The responses of residents in sample blocks may be affected by their awareness of the presence of ICM interviewers, particularly if an ICM inter
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From page 116... ...
· NRF7U interviewers may become aware of the presence of ICM interviewers and make special efforts in ICM sample blocks to obtain more complete follow-up results than in other blocks. · We expect that some housing units missed by the MAP in non-ICM blocks will still get counted (census adds)
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From page 117... ...
Because in ICM blocks the ICM sample is accumulated on a flow basis as the census enumerations and NRFU are accumulated, it becomes important to determine whether information added actually pertains to residence on Census Day. If, for example, enumerations in the ICM samples add people who moved into the blocks in question after Census Day, then this would create an upward bias in the population total, with an obvious effect on the validity of estimates.
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From page 118... ...
We mention several of them here. · The Census Bureau intends to experiment with use of administrative records as part of integrated coverage measurement (see Chapter S)
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From page 119... ...
STATISTICAL ESTIMATION Estimation and the One-Number Census Census design features being considered for 2000 will create new demands for statistical estimation methods. Each of the methods described previously in this chapter sampling of nonresponse follow-up and integrated coverage measurement requires a corresponding estimation strategy and research on particular aspects of implementation, as do some uses of administrative records and other additional sources of information.
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From page 120... ...
· Additional information sources. Inclusion of new information sources into the census, such as administrative records and multiple response modes, may create new demands on estimation methodologies.
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From page 121... ...
. Estimation Methods for NRFU Sampling If NRFU is conducted in a sample of households, it will be necessary to calculate estimates of numbers and characteristics of households at addresses that were not included in the NRFU sample.
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From page 122... ...
The 1995 census test results will primarily answer questions about operational and cost issues associated with NRFU sampling. Estimation Methods for ICM: Estimating Factors In the 1990 undercount estimation program, adjustment factors were calculated for domains or cells defined by geography and population characteristics that cut across state lines.
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From page 123... ...
, while the second and third factors are based on the coverage measurement survey (hence the distinction between C and CO)
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From page 124... ...
Estimation Methods for ICM: Carrying Estimates Down to Lower Levels Let us assume for the moment that adjustment factors for cells have been calculated. Because the geographic detail for cells will almost certainly be much coarser than many of the units for which estimates are required (such as census tracts or small political subdivisions)
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From page 125... ...
This question has been approached through theoretical investigation and through simulations based on coverage measurement data and census data for other variables than the undercount. Further research in this area before the 2000 census would make a useful contribution to design and validation of the estimation methodology.
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From page 126... ...
Selection of estimators must be guided by an awareness that, although for some purposes state estimates are the most important product of the census, for other purposes the distribution of population within states, for example by race and urbanicity, is paramount. Recommendation 4.5: The Census Bureau should prepare alternative sample designs for integrated coverage measurement with varying levels of support for direct state estimation.
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From page 127... ...
There are two difficulties inherent to this approach. First, simple estimation methods such as those described above for ICM estimation produce adjustment factors that can be used to calculate expected numbers of people.
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From page 128... ...
There are important interactions between ICM sample design, estimation methods, and the units for which ICM accuracy is measured. The ICM sample must be designed to give acceptable accuracy for important units such as those listed above.
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From page 129... ...
Demographic analysis possesses a number of potential strengths as a method for coverage evaluation in the 2000 census: operational feasibility, timeliness (estimates could be available early in the census year) , low cost, independence of
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From page 130... ...
However, based on the current state of research, we doubt that demographic analysis could be used in the 2000 census to adjust (or benchmark) final population estimates as part of integrated coverage measurement.
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From page 131... ...
Recommendation 4.6: The panel endorses the continued use of demographic analysis as an evaluation tool in the decennial census. However, the present state of development does not support a prominent role for demographic methods in the production of official population totals as part of integrated coverage measurement in the 2000 census.
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From page 132... ...
Another common concern was that confusion would be created by having two sets of results, those before and after adjustment. By prespecifying estimation methods as much as possible, the Census Bureau makes it clear that decisions have been made on good statistical principles and judgment, rather than being motivated by any consideration of how they will affect particular areas.
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From page 133... ...
Analytical uses of these data require availability of both point estimates and measures of uncertainty. When complex statistical methods, such as complex sampling schemes, indirect estimation, and imputation are used in creating census products, users will not be able to derive valid measures of uncertainty by elementary methods, and they may not have adequate information in the published or available products to derive these measures.
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From page 134... ...
In the final phase, beginning with assessment of the 1995 census test and continuing through the decade, the selected estimation methods will have to be consolidated, optimized, validated, and made both theoretically and operationally robust. This last process will ensure that they can stand up to critical scrutiny and to problems that may arise in the course of the 2000 census.
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From page 135... ...
Topics should include nonresponse follow-up sampling, coverage estimation, incorporation of varied information sources (including administrative records) , and indirect estimation for small areas.
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