Using the American Community Survey Benefits and Challenges (2007) / Chapter Skim
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6 Weighting and Interpreting ACS Multiyear Estimates
6 Weighting and Interpreting ACS Multiyear Estimates
Pages 209-224
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From page 209... ...
The previous chapter has described the weighting methods being used to produce 1-year period estimates, combining all the data collected within a calendar year. This chapter examines the weighting methods that the Census Bureau is planning to use to produce 3-year and 5-year period estimates.
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From page 210... ...
Other changes that potentially affect multiyear period estimates, such as changes in geographic boundaries or question wording, and the problem of discontinuities in population and housing controls around the time of the 2010 census are addressed elsewhere in the report. 6-A ALTERNATIVE ESTIMANDS FROM MULTIYEAR DATA During the panel's early deliberations, various alternative estimands based on 3- and 5-years of ACS data were under consideration.
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From page 211... ...
WEIGHTING AND INTERPRETING ACS MULTIYEAR ESTIMATES time. In the simplest case in which the 1-year parameters are assumed constant across time, then the optimum choice for the values for the wi is to set them all equal (i.e., wi = 0.33 for 3-year estimates, or wi = 0.2 for 5-year estimates)
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From page 212... ...
. A variant of this simple approach takes advantage of revised, updated housing and population controls for earlier years in the period, which may have become available by the time when the weights for the period estimates are being developed.
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From page 213... ...
Instead of applying these factors separately for each year, they are applied to the concatenated sample for the multiple years. The housing unit and population controls used are the averages of the 1-year controls for the multiple years, using any revisions that have been made to the controls since the 1-year period estimates were first produced.
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From page 214... ...
Elsewhere in this report the panel has pointed out the need to improve the precision of ACS estimates for small geographical areas. Thus, this line of research warrants further investigation.
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From page 215... ...
It is only when two 5-year period estimates are 5 or more years apart that there is no overlap. The extent of overlap between two multiyear estimates determines the estimand that the difference between them is estimating.
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From page 217... ...
. Under the second scenario, the annual population values can be represented as Y for the first 3 years and Y + g thereafter.
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From page 218... ...
To aid understanding of the relationship between the different estimands and their standard errors, Table 6-3 summarizes results on standard TABLE 6-3 Standard Errors of Estimates of Change for Various Values of the Gap Between Two Period Estimators as Multiples of the Standard Errors of a 1-Year Estimator Gap Between Period Estimates (Years) Period Estimator 1 2 3 4 5 or more 1-year 1.41 1.41 1.41 1.41 1.41 3-year 0.47 0.67 0.82 0.82 0.82 5-year 0.28 0.40 0.49 0.57 0.63 NOTE: See text for explanation of multiples.
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From page 219... ...
The fact that 3-year estimates are being compared in a situation in which a 1-year estimate with a standard error of s is deemed too imprecise to be published implies that change estimates between overlapping 3-year estimates are very imprecise -- they have standard errors as large as or larger than a 1-year estimate. The same situation applies with estimates of differences between overlapping 5-year estimates.
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From page 220... ...
Of course, the multiyear period estimates remain an improvement over the once-a-decade long-form sample because they are updated every year and therefore provide a more timely picture of the characteristics of an area than is possible from the long-form sample. A final point regarding differences between multiyear period estimates is that, just like the estimates themselves, they can reflect a variety of pat
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From page 221... ...
The Census Bureau's planned weighting procedures for multiyear estimates reflect such changes by using the 3- or 5-year averages of the independent housing unit estimates and the independent population estimates by demographic subgroup as controls. Users need to consider the potential effects of the planned weighting scheme on ACS estimates.
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From page 222... ...
The simplest model assumes for the county that the prevalence rates for the characteristic of interest have remained approximately constant over the estimation period within demographic subgroups and that the population estimates by demographic subgroup for the latest year are accurate. The ACS multiyear period estimates are then used as estimates of the latest-year prevalence rates within specified demographic subgroups, and these rates are applied to the latest-year county population estimates for those subgroups.
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From page 223... ...
WEIGHTING AND INTERPRETING ACS MULTIYEAR ESTIMATES Recommendation 6-2: The Census Bureau should consult users about the utility of the currently proposed multiyear period estimates -- par ticularly for estimates of totals -- for areas that change markedly in population size. It should investigate whether there are other forms of estimates that could be produced and would better serve user needs.
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