Medicaid at Birth, WIC Takeup, and Children's Outcomes
Research Center: Institute for Research on Poverty, University of Wisconsin-Madison
Investigator: Bitler, Marianne, and Janet Currie
Institution: RAND Corporation
Public Policy Institute of California
500 Washington St.
San Francisco, CA
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
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.