cases in which family living arrangements and resource sharing are complex. For example, it is not always clear how many people are a part of the family or “economic unit” and thus whose income counts in determining income eligibility when multiple families share resources and expenses. In some cases, there is more than one way to count the number of members and the incomes of the economic unit. As we discuss further in this chapter, WIC rules allow state and local agencies some flexibility in how the economic unit and other eligibility definitions are applied. As a result, there may be variation in how eligibility rules are applied. Variation in how rules are applied in the field creates uncertainty in estimates of the number of persons eligible. We discuss below a few areas in which the eligibility criteria are ambiguous enough to be applied differently for different situations. Our intent is to emphasize possible sources of variation for eligibility estimates—not to point out problems with the regulations and how they are interpreted in determining WIC eligibility.
In this section, we also discuss ambiguities in other eligibility concepts in which the definition of eligibility can be interpreted broadly or narrowly. For example, women who are pregnant are technically categorically eligible for WIC for their entire pregnancy, even though a woman is likely not to know she is eligible right away. A broad definition of eligibility may assume that women are categorically eligible as soon as they become pregnant, while a narrow definition may consider women categorically eligible as soon as their pregnancy is confirmed. Again, the purpose of this discussion is to introduce areas in which measurement of eligibility is a tricky concept that may result in systematic biases in estimates depending on what one sees as the true definition of eligibility.
Five groups are eligible for WIC: infants, children ages 1 to 5, pregnant women, nonbreastfeeding women up to 6 months postpartum, and breastfeeding women up to 12 months postpartum. The latter three are not as easily identified in measuring eligibility. Given the example above, it is not clear if, for the purposes of estimating eligibility, a pregnant woman should be considered categorically eligible as soon as she becomes pregnant or as soon as her pregnancy is confirmed. As we detail later, current methods for estimating eligibility count women as eligible for a full 9 months of pregnancy. In practice, however, a lag occurs between conception and the confirmation of pregnancy. The current methodology is