Paul Ong

The decennial census is America’s single most important effort to collect data on its population, and yet the count always comes up short. Over the years, the counts have been getting somewhat better, although it’s still nearly impossible to include everyone. Estimates of the uncounted population declined steadily from 5.4 percent in 1940 to 1.2 percent in 1980, then increased to 1.8 percent in 1990. Preliminary estimates for 2000 range from 0.96 to 1.4 percent. One troubling aspect of the undercount is the sizable variation among groups—what’s called the “differential undercount,” because groups are undercounted differently. Preliminary estimates for the 2000 census show undercount rates for minorities that are several times higher than rates for non-Hispanic whites—three times higher for African Americans, four times higher for Hispanics, and seven times higher for American Indians on reservations. Undercount rates also vary by region, level of urbanization, and home ownership.

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