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National Research Council (US) Panel to Evaluate the USDA's Methodology for Estimating Eligibility and Participation for the WIC Program; Ver Ploeg M, Betson DM, editors. Estimating Eligibility and Participation for the WIC Program: Phase I Report. Washington (DC): National Academies Press (US); 2001.

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Estimating Eligibility and Participation for the WIC Program: Phase I Report.

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2Program Eligibility

The language of the congressional act that established the WIC program states the reason for the programs establishment: “Congress finds that substantial numbers of pregnant, postpartum, and breastfeeding women, infants and young children from families with inadequate income are at special risk with respect to their physical and mental health by reason of inadequate nutrition or healthcare, or both” (Sec. 17 [42 U.S.C. 1786] of the Child Nutrition Act of 1966). “It is, therefore, the purpose of the program…to provide…supplemental foods and nutrition education…. The program shall serve as an adjunct to good health care, during critical times of growth and development, to prevent the occurrence of health problems, including drug abuse, and improve the status of these persons.” This language is clear about the types of persons (categories) intended to be served—pregnant and postpartum women, infants, and young children with inadequate incomes. Later in the text of the act, the three overall criteria for WIC eligibility are delineated: categorical eligibility, income or adjunct eligibility, and nutritional risk.1 If a person meets all of these criteria, he or she is “fully eligible” for the program.

Although the concept of eligibility intended by Congress in this act may seem straightforward, it can be difficult to determine eligibility in 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 consistent with the rules of eligibility in that, technically, a woman is eligible as soon as she becomes pregnant. However, because of the timing lag, 100 percent participation of eligible women defined in this way would never be possible. Thus, in theory, a narrow definition of eligibility could consider someone eligible for only the period after pregnancy is confirmed.

Data on the lag between conception and pregnancy confirmation are not available. However, data on when pregnant women enroll in WIC are available. The 1998 WIC Participant and Program Characteristics Report indicates that 47 percent of pregnant women who participated in WIC enrolled in the program during the first trimester of pregnancy, 38 percent enrolled in the second trimester, and 12 percent enrolled in the last trimester (4 percent did not report data) (U.S. Department of Agriculture, 2000a). Thus, at least half of the pregnant women participating in WIC did not enroll until they were at least 4 months pregnant.

Postpartum women are eligible for WIC for 6 months if they do not breastfeed their infant or for two 6-month certification periods (up to a year postpartum) if they are breastfeeding. Women who breastfeed at least once a day on average are conferred breastfeeding status. Women who stop breastfeeding before the end of a certification period will be identified as nonbreastfeeding only if they visit a WIC clinic to request a change in the infant's food package.


The WIC income verification process is, in general, less burdensome than the income verification processes of other public assistance programs, such as Temporary Assistance for Needy Families (TANF) and food stamps. Until recently, states could determine what documentation of an applicant's income was needed to verify eligibility. Standards for income documentation varied quite a bit across states. For example, in 1998, only 51 percent of local agencies required income documentation (U.S. Department of Agriculture, 2000a). However, legislation passed in 1998 implemented standard income documentation requirements for applicants who are not adjunctively income eligible for WIC.

State and local agencies are still given some flexibility in how they determine income eligibility. Specifically, WIC personnel have some discretion in defining the economic unit (i.e., the family unit) and the period of time over which income should be counted. Technicalities of how adjunctive eligibility is defined also give some flexibility to WIC personnel in assessing adjunctive eligibility status. We discuss each of these flexibilities and how they can introduce errors into the process of estimating WIC eligibility.

Economic Unit

Defining the economic unit determines which household members' incomes are counted and how many people are part of the economic unit when income eligibility is assessed. WIC program regulations use the following definition of an economic unit: “a group of related or nonrelated individuals who are living together as one economic unit” (U.S. Department of Agriculture, 2000b:295). A WIC policy memorandum interprets these regulations (Final WIC Policy Memorandum 99–4:8):

It is reasonable to assume that persons (other than those living in institutional settings and homeless facilities) living in the residences of others, whether related or not, are likely to be receiving support and some commingling of resources which renders them members of the economic unit with which they live. However, it is possible to establish that more than one economic unit lives under one roof through appropriate questioning, which helps to make a reasonable determination that there is general economic independence of the units, i.e., that financial resources and support are retained independently. For example, a pregnant woman who is sharing an apartment with her sister may be determined to be a separate economic unit from her sister if the certifier can reasonably establish that she has a source of income and is paying her proportionate share of household, living and personal expenses.

Assessing which members of a household are part of the economic unit therefore implies that individual WIC staff members may need to ask applicants a series of detailed questions about their living situations and with whom and how they share incomes and expenses. In the example of a pregnant woman, the WIC staff member must sort out whether the pregnant woman has an income source and whether she pays her proportionate share of the household's expenses. It is unlikely that all caseworkers will ask the same questions to determine who pays what and how much, and therefore it is unlikely that all WIC staff members will make the same eligibility assessment, even when serving people with identical circumstances. Some WIC staff members may be generous in assessing who is part of the family unit, while others may be strict. In this report, we consider both a generous definition—one that considers whichever family unit makes the applicant eligible as the correct definition—and a restrictive definition—one that considers whichever definition makes the family ineligible.

Accounting Period for Income

The definition of income (that is, what sources count) is clearly laid out in the regulations (see Chapter 3). However, the regulations concerning the time frame over which income should be measured are vague and present problems for operationalizing an accounting period for estimating eligibility (U.S. Department of Agriculture, 2000b:307):

In determining the income eligibility of an applicant, the State agency may instruct local agencies to consider the income of the family during the past 12 months and the family's current rate of income to determine which indicator more accurately reflects the family's status. However, persons from families with adult members who are unemployed shall be eligible based on income during the period of unemployment if the loss of income causes the current rate of income to be less than the State or local agency's income guidelines for Program eligibility.

Although an instruction memo provides some guidance, it still leaves the states with considerable flexibility (Food and Nutrition Service Instruction Memo 803–3:5):

State agencies have, and should exercise, flexibility in deciding whether to use an applicant's current or annual rate of income. For example, the family of a striker may have a lower income during the period of a strike (depending on the union benefits and other sources of income), but have an annual income which would exceed the WIC limit. In this case, the use of current income (while on strike) may be more appropriate. However, in the case of families of self-employed persons, including farmers or seasonally employed persons whose income fluctuates, annual income may be the more appropriate indicator of the need for WIC benefits. Other examples in which the use of annual income is more appropriate include: (1) a family member who is on a temporary leave of absence from employment, such as maternity leave or to take an extended vacation; (2) teachers who are paid on a 10-month basis and are temporarily on leave during the summer months; and (3) college students who work only during the summer months and/or their school breaks.

Again, the accounting period for income is subject to state discretion. Variation in how local WIC staff workers apply rules about the accounting period for income creates the potential for errors in estimating eligibility because definitions of income used to estimate eligibility may not exactly match definitions of income as they are applied by local WIC offices in assessing eligibility.

Adjunctive Eligibility

Adjunctive eligibility rules further complicate efforts to measure eligibility. A person is adjunctively eligible for WIC and does not need to go through the WIC income certification process if she can document that she is certified fully for the Food Stamp, Temporary Assistance for Needy Families (TANF) or Medicaid programs. The regulations read (Final WIC Policy Memorandum 99–4:6):

By law, persons and/or certain family members certified as eligible to be enrolled in any of these [Food Stamp Program, TANF, or Medicaid] at the time of their application to WIC are adjunctively eligible for WIC, and… are not subject to the income guidelines used for traditional WIC income eligibility certification.

Because of differences among states in eligibility rules (some states have Medicaid income eligibility thresholds above 185 percent of poverty guidelines), it is possible to be income ineligible for WIC but income eligible for Medicaid.2 Thus, in a broad sense, everyone who is eligible for Medicaid (or food stamps or TANF) is also eligible for the WIC program. The regulation that a WIC applicant must be enrolled in the Food Stamp Program, TANF, or Medicaid to be adjunctively eligible for WIC is really a technicality, since all the applicant needs to do is apply and enroll in one of these three programs to be eligible for WIC. A WIC staff member assessing eligibility of a WIC applicant may find that the applicant has income greater than the WIC eligibility threshold but less than the Medicaid threshold. The applicant may be encouraged to enroll in Medicaid, which would make them eligible for WIC. This would not be inconsistent with the intent of the program to serve as an adjunct to improved health.

Therefore, one measure of how many people are adjunctively eligible for WIC is the number eligible for the Food Stamp Program, TANF, or Medicaid. However, not everyone who is eligible for Medicaid, TANF or food stamps will enroll in them, so this measure may not accurately reflect the number of people who are currently enrolled in the program—and therefore adjunctively eligible for WIC. To accurately estimate how many people are adjunctively eligible for WIC, it is not clear if it is more appropriate to make an estimate that considers all those who are eligible for the other programs eligible for WIC, or to make an estimate that considers only those enrolled in the other programs eligible for WIC. We return to this issue later in the report.


The final step in determining eligibility is assessing nutritional risk. To be fully eligible for the program, a competent professional authority must determine that an applicant meets at least one of the many nutritional risk criteria allowed. Prior to 1998, states had a great deal of discretion on what criteria were used to assess nutritional risk. Now nearly all criteria are standardized across states. In practice, however, it appears that very few income eligible people fail to meet at least one of the nutritional risk criteria. In Chapter 4, we consider current assumptions about the proportion of income eligible individuals who are at nutritional risk and methods and data used to estimate nutritional risk.


The true pool of eligible persons depends on how the eligibility rules for the program are set, which is the policy choice Congress makes. This chapter has highlighted some components of the eligibility rules that are not always easily applied to every family that comes into a WIC office. The lives of those who apply for WIC can be quite complex, and it would be very difficult to define eligibility rules that could apply to every case that seeks assistance. As a result, there are components of the eligibility rules for which local WIC offices are given considerable flexibility in applying the rules. The consequence is that any estimates of eligibility will be made with uncertainty, simply because program rules may not be applied in a standardized way. The purpose of this discussion is not to suggest that more or less standardization of the rules is needed—that is not the panel's charge and it is actually quite clear from the regulations and their instructive guidance that much discretion has purposefully been given to the states. Rather, our purpose in highlighting the difficulties in applying eligibility rules is to illustrate a source of uncertainty in estimating eligibility. The panel's task is to consider the best scientific methods for estimating eligibility according to the laws Congress has set.



Residency in the state or local service area to which the applicant is applying is also a requirement for eligibility.


See Lewis and Ellwood (1998) for a review of differences in Medicaid and WIC eligibility rules.

Copyright 2001 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK223563


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