native data sources, such as the Survey of Income and Program Participation; the timeliness of the data used in the estimation; and assumptions concerning breastfeeding rates among postpartum women. In the second phase of the study, the panel plans to consider these issues as well as others, which are outlined in Chapter 6.

ACCURACY OF THE CURRENT POPULATION SURVEY

The primary database for FNS’s annual estimates of the number of income eligible infants and children is the March supplement of the CPS. This nationally representative survey of the population collects demographic and income information from over 55,000 American households. Utilizing the CPS information on the number of family members, family income, and age of persons in the family, FNS makes two core estimates: (1) the number of infants who live in families whose annual income is less than 185 percent of federal poverty guidelines and (2) the number of children who live in families whose annual income is less than 185 percent of federal poverty guidelines. While the accuracy of both of these core estimates is crucial, the accuracy of the estimates of the number of infants is especially important for two reasons. First, the number of income eligible infants is the base from which the number of pregnant and postpartum women eligible for WIC is inferred. Hence any errors in estimating the number of income eligible infants would also be reflected in the estimates of the number of income eligible women in these groups. Second, high estimated coverage rates of infants and postpartum women led the panel to question whether the numbers of eligible people in these groups were being properly estimated.

To consider the accuracy of the CPS estimates of total number of infants and children, the panel asked the Census Bureau to make a presentation at the panel’s Workshop on Estimating WIC Eligibility and Full-Funding Participation. Notes from the presentation by Gregory Spencer of the Census Bureau Division of Population Estimates were given to the panel for its consideration (Spencer, 2001). To assess the accuracy of the CPS estimates, Spencer (2001) compared weighted CPS sample estimates of the numbers of infants and children to the CPS control totals. These control totals are estimated from the Census Bureau’s annual estimates of the noninstitutionalized U.S. population of infants and children (which are produced using birth and death records from vital statistics data with an adjustment for migration) plus an adjustment for the net undercount in



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