Medicaid at Birth, WIC Takeup, and Children's Outcomes

Year: 2003

Research Center: Institute for Research on Poverty, University of Wisconsin-Madison

Investigator: Bitler, Marianne, and Janet Currie

Institution: RAND Corporation

Project Contact:
Marianne Bitler
Research Fellow
Public Policy Institute of California
500 Washington St.
San Francisco, CA
Phone: 415-291-4491


The Special Supplemental Nutrition Program for Women, Infants and Children (WIC) provides participants with supplemental foods, nutrition education, and health referrals. While WIC was originally established to address malnutrition and hunger, today many children are at risk of obesity. The Surgeon General's 2001 report on obesity emphasizes the importance of early intervention to prevent obesity, since eating habits are hard to change once they are formed. Hence, the prevention of overweight and obesity is now an important goal of WIC. This study examined to what extent WIC is meeting this goal among young children.

Most previous research focuses on WIC participation during pregnancy and on birth outcomes. This study examined the WIC participation rate among eligible 4-year-old children (which is referred to as WIC takeup) and documented the effect of childhood WIC participation on risk of obesity. The study used data on WIC participation, child anthropometrics, health, and health care utilization from the 1996 and 2001 panels of the Survey of Income and Program Participation (SIPP). The main empirical challenge in this study was to account for the possibility that women select into WIC based on unobservable characteristics that also affect their health outcomes. For example, if women in poor health are more likely to participate in WIC, then standard estimation procedures will lead to biased estimates of the effect of WIC on health outcomes. The authors showed that recent changes to the Medicaid program had significant effects on WIC takeup, and used the Medicaid changes as instruments to identify the effects of WIC on child outcomes.

WIC participation among children may have been affected by two recent changes to the Medicaid program. First, higher Medicaid cutoffs for infants are likely to affect childhood WIC participation because most children who use WIC began using the program as infants, and Medicaid confers automatic eligibility for WIC. The authors showed that higher Medicaid cutoffs during infancy induced the infants' mothers to join both Medicaid and WIC, and that some fraction of these new entrants remained on the program through early childhood.

The second Medicaid eligibility change occurred through the State Child Health Insurance Program (SCHIP). Under SCHIP, States were given the option of extending public health insurance to uninsured children either by expanding Medicaid or by creating a separate, standalone program (or by some combination). Because Medicaid participants are eligible for WIC, States that used SCHIP to expand Medicaid also expanded eligibility for WIC among children. However, the study showed that these changes had little impact on children's WIC participation, suggesting that it is difficult to enroll children who did not participate as infants.

In the instrumental variables models, WIC participation at age four is associated with a large and statistically significant reduction in the probability that children are at risk of overweight (defined as having a Body Mass Index above the 85th percentile for sex and age). WIC has no significant effect on use of health care, which supports the interpretation that the effects on weight are due to the nutritional component of the WIC program rather than to any links between WIC and current access to medical care.

The study results suggest that either the nutrition education, the provision of nutritious foods, or both helps prevent obesity among young children. An important caveat is that the close link between Medicaid coverage of the birth, WIC participation during infancy, and WIC participation during childhood makes it difficult to isolate the net effect of WIC during childhood.