Box 5-1) are retained, but then noninterview factors 1 and 2, the mode bias noninterview factor, and the housing unit control and population control factors are applied differently. 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. The advantage of the Census Bureau’s method is that, by pooling the sample across years first, the controls are applied to a larger sample. (This is also an advantage for the noninterview adjustments.) As a result, greater control on the population counts by age, sex, and race/ethnicity within estimation areas is possible because less collapsing of control cells is needed.

There are trade-offs to be considered between the simple approach and the Census Bureau’s planned approach. The Census Bureau’s approach gives greater control on demographic characteristics but lacks control over the yearly representation of the sample. The simple scheme has the benefit of ensuring that each year is represented in its right proportion in the estimation process but employs control over the demographic characteristics only to the extent that this is achieved for the 1-year estimates.

While the greater control on the demographic controls afforded by the Census Bureau’s scheme appears attractive, the issue of the quality of those controls must be considered. As discussed in Section 5-D, the panel has serious concerns about the quality of the population estimates at this level of detail and recommends that the Census Bureau should carry out research on this step in the 1-year weighting process, including alternative possibilities of less detailed demographic controls, applying the controls on a marginal basis by raking, or applying the controls at a higher level of aggregation. The results of this research may lead to a population control weighting step that does not require the collapsing of control cells. In this case, the simple scheme for producing multiyear weights by dividing the 1-year weights by the number of years, or rather the variant of it with updated controls, may be preferred because it also provides temporal control. Research is needed in this area.

Another area of research on multiyear weighting is to investigate the application of the housing unit and population controls at the county level rather than at the estimation area level used in the 1-year weighting. A key concern is whether the housing unit and population estimates for small counties are of adequate quality for this use. A possible approach would be to apply a housing unit control at the county level and to use a raking algorithm to apply a total population control at the county level and demographic controls at the estimation level. (Total population and housing unit controls could also be applied for cities within counties.) Note that



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