considered as part of the recent redesign of the main CPS (except those changes, such as the sample redesign and the introduction of CAPI/CATI, that apply to the entire survey), and the research program on data quality is limited. SIPP will undergo a major redesign to improve the usefulness of the data (notably the extension of each panel to 48 months), which will likely include changes and improvements to the questionnaire. SIPP also has an active research program to investigate and improve data quality (see Jabine, King, and Petroni, 1990).

Population Undercoverage

It is well known that household surveys rarely cover the population as well as the decennial census (see Shapiro and Bettin, 1992; Shapiro and Kostanich, 1988). SIPP and the March CPS are no exception. Thus, even after adjustment for survey nonresponse, the SIPP data for March 1984 covered only 85 percent of black men and 91-93 percent of all other people when compared with census-based population estimates, while the March 1984 CPS covered only 84 percent of black men and 90-94 percent of all others. By age, black men in the 20-39 age categories were generally the worst covered. Coverage ratios were even worse in March 1986 for black men for both SIPP and the March CPS—80 and 82 percent, respectively (Jabine, King and Petroni, 1990: Tables 10.12, 10.13). More recent data indicate that the situation has not improved: the March 1992 CPS covered only 79 percent of black men, 87 percent of black women, and 90-95 percent of white and Hispanic men and women (Coder, 1992a: Table C-1).8

The Census Bureau uses ratio-estimation procedures to adjust SIPP and March CPS survey weights for population undercoverage. The weights are adjusted so that the population estimated from the surveys agrees with the updated decennial census-based population estimates by age, sex, race, and Hispanic origin. SIPP weights are also adjusted to agree with the March CPS weights by household type. However, these ratio adjustments do not correct all coverage errors. First, they do not correct for the undercount in the decennial census itself: although it is minimal in total—net undercount was estimated to be between 1 and 2 percent of the population in 1980 and


Other household surveys, including the Consumer Expenditure Survey, also exhibit population undercoverage (see Shapiro and Bettin, 1992). Recent work indicates that population undercoverage in surveys may not be as high as previously believed, relative to the decennial census, when comparisons are made that exclude census overcounts (see Shapiro, Diffendal, and Cantor, 1993). However, survey undercoverage rates remain high: for example, the undercoverage rate for black males was 89 percent in the February, May, August, and November 1990 CPS, when compared with a 1990 census estimate adjusted for overcounts (versus 84% when compared with an unadjusted estimate). Moreover, these rates do not include the undercount in the census itself relative to demographic estimates of the population.

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