Thus, we can summarize the data in Table 5-1. The DA base estimate for 2000 of 279.6 million is 1.8 million lower than the census count of 281.4 million, implying a net overcount in the census of 0.7 percent. However, the A.C.E. estimate is 284.7 million, which implies a net undercount in the census of 3.3 million (1.2%). There is a need then to reconcile a difference of 5.1 million between the two estimates—base DA and A.C.E. —to come to closure in choosing the “best” estimate for evaluating the census count of the U.S. population in 2000.3 The alternative DA estimate developed by the Census Bureau reduces the difference from the A.C.E. estimate somewhat, but not entirely (the difference decreases from 5.1 million to 2.4 million).

By age and sex, coverage patterns estimated by DA are broadly similar between 1990 and 2000 in that women were better counted then men, and older people were better counted than younger people. The 1990 PES and 2000 A.C.E. also show these patterns. However, the 2000 DA net undercount estimates are much lower than the 1990 DA estimates, even when the 2000 DA population estimates are adjusted to allow for a greater number of undocumented immigrants than originally estimated; see Table 5-2.


The main area of uncertainty in the DA estimate of the total population lies with the immigration component, especially the number of undocumented immigrants. Other components, such as emigrants and some categories of legal immigrants, also add to the margin of error.

The DA base estimate assumes that there are about 6.0 million undocumented immigrants living in the United States under age 65–3.3 million from the 1990 DA estimate plus a net increase during the 1990s of 2.7 million.4 The estimated net increase during the decade essentially represents an extrapolation of net undocumented immigration derived from estimates that mainly reflect changes between 1992 and 1996. Considering a number of factors, Census Bureau researchers believe that 6 million is a reasonable lower-bound estimate of the number of undocumented immigrants at the time of the 2000 census (Robinson, 2001a). For purposes of comparative analysis, the Census Bureau simply assumed a doubling of net undocumented immigration over the decade, to 8.7 million (bringing the total population to 282.3 million. This alternate estimate (see Table 5-1) implies a census undercount of 0.9 million, or 0.3 percent, still far below the 3.3 million (1.2%) indicated by the A.C.E.


In 1990, in contrast, the DA estimated a higher net undercount than that estimated by the Post-Enumeration Survey (PES). The DA estimate of the net undercount was 1.9 percent; that of the PES was 1.6 percent.


For people age 65 and over the adjustment for Medicare underregistration presumably includes undocumented immigrants. See Robinson (1991) for a discussion of the Medicare adjustments for the 1990 DA estimates.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement