coverage, and this is what is relevant to the allocation of political representation and public funds. This net undercoverage affects some groups more than others—that is, the census has differential (net) undercoverage—and there are demographic groups for which this differential undercoverage has persisted over several censuses.

The 1950 through 1990 decennial censuses all made use of various evaluation programs to assess the extent of gross and net census undercoverage and its causes. The only cost-effective methodology available for measuring the degree of differential undercoverage for subnational areas is a large-scale post-enumeration survey coupled with dual-system estimation.

Dual-system estimation, the methodology used in 1990 to join the information from the post-enumeration survey and the census to measure net census undercoverage, depends on several assumptions. After considering the criticisms related to the validity of, and the impact of departures from these assumptions, which have been used to argue against the use of integrated coverage measurement to produce official population counts, the panel concludes that the criticisms of this approach are not compelling reasons to halt plans to use integrated coverage measurement in 2000. If the Supreme Court prohibits use of integrated coverage measurement for apportionment, the panel still strongly supports a post-enumeration survey of the currently budgeted size of 750,000, for purposes other than apportionment.

Estimation Methods

The decennial census, as planned for 2000, will require estimation methods that were not needed or used in 1990. They include supplying imputed records as a result of sampling for nonresponse follow-up and for carrying the results of the dual-system estimation down to small areas. The Census Bureau has made an effort to keep these estimation methods as simple as possible. While the panel supports this decision for the 2000 census, it hopes that several more promising techniques can be adequately tested over the next decade and used in 2010 if shown to have advantages over the techniques used in 2000.

Experimentation in the 2000 Census

As the U.S. population continues to change in various ways, the best methods for enumerating the population also change. Therefore, a cycle of experimentation and data collection during a census followed by evaluation, further development, and experimentation and testing between censuses, is necessary for an effective census methodology. The decennial

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