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RESEARCH AND PRACTICE |
At the time of this investigation, Jessica Y. Lee was a PhD candidate in health policy and administration at the University of North Carolina, Chapel Hill, School of Public Health. R. Gary Rozier and Edward C. Norton are with the Department Health Policy Analysis and Administration, University of North Carolina, Chapel Hill. William F. Vann Jr is with the Department of Pediatric Dentistry, University of North Carolina, Chapel Hill. Jonathan B. Kotch is with the Department of Maternal and Child Health, University of North Carolina, Chapel Hill.
Correspondence: Requests for reprints should be sent to Jessica Y. Lee, DDS, MPH, PhD, Department of Pediatric Dentistry, CB 7450 Brauer Hall, Carolina Campus, Chapel Hill, NC 275997450 (e-mail: jessica_lee{at}dentistry.unc.edu).
| ABSTRACT |
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Objectives. We estimated the effects of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) on dental services use by Medicaid children in North Carolina.
Methods. We used linked Medicaid claims and enrollment files, WIC files, and the area resource file to compare dental services use for children enrolled in WIC with those not enrolled. We used multivariate models that controlled for child clustering and employed 2-step methodology to control for selection bias.
Results. Children who participated in WIC had an increased probability of having a dental visit, were more likely to use preventive and restorative services, and were less likely to use emergency services.
Conclusions. Childrens WIC participation improved access to dental care services that should lead to improved oral health.
| INTRODUCTION |
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| WIC and Medical Care |
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Few studies have addressed the effects of WIC on the utilization of health care services.3,6,10 One investigation demonstrated that WIC participants used a childrens clinic more frequently than did nonparticipants.12 In a recently published study, Buescher et al. reported that "Medicaid-enrolled children participating in the WIC program use all types of health care services compared with Medicaid-enrolled children who were not WIC participants."13(p145) They concluded that "the health care needs of low-income children who participate in WIC may be better met than those of low-income children who were not WIC participants."13(p145)
| WIC and Oral Health Care |
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Findings from previous WIC and health care utilization investigations are further limited because they do not control for the nonrandomized nature of WIC participation.13,16 We build on these past studies in an investigation of WIC participation and use of dental services by using claims data rather than self-reports and by employing multistage modeling to control for selection bias. Using these more sophisticated analytic techniques in our exploration of the effects of WIC on use of oral health services, we provide an estimate of the effectiveness of WIC programs in linking clients with dental providers. Specifically, we determined whether, compared with Medicaid children who did not participate in WIC, preschool-aged Medicaid children enrolled in WIC had an increased likelihood of having had a dental visit and whether it was of a certain type (preventive, restorative, or emergency.
| METHODS |
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Data Sources and Study Cohort
We used the following linked North Carolina administrative data sets for our investigation: composite birth records, Medicaid eligibility enrollment files, Medicaid dental claims, WIC files, and the area resource file. The linkage process for these files has previously been reported, and a matching rate of 98.5% was etablished.13
All children born in North Carolina in calendar year 1992 who were enrolled in the Medicaid program were eligible for inclusion in the study. Children were excluded if they had more than 1 Medicaid identification in their records (759 children) or if they had recorded periods of Medicaid enrollment indicated before the date of birth (1371 children). A Medicaid enrollment history was created for each child in which enrollment status was indicated for each month of life from birth to the age of 5 years (months 1 through 60).
Analysis Strategy
Using various multiple regression analyses with control variables, we determined the relation of childrens WIC participation and the use of oral health services. Several analytic challenges had to be considered. Because our investigation followed children for 5 years, the data set contained multiple observations per child that can result in correlated error terms and bias results. To control for this problem, we used robust standard errors and controls for clustering around the child in the regression analysis. Panel data techniques using random effects models were used in each analysis.
Another important analysis consideration was the potential for selection bias. Because WIC participation was not randomly determined among Medicaid children, we anticipated that children who participated in WIC would more likely be users of health care services than other Medicaid children. This assumption suggests the potential for correlation between the WIC participation variable and the error term of our main analysis. Failure to account for this correlation could bias our results. To control for this potential bias, we incorporated a 2-stage multilevel model using instrumental variables as outlined by Bollen et al.17 We screened potential instrumental variables for their close association with WIC participation. Three instrumental variables (number of WIC clinics per county, number of full-time WIC workers per county, and WIC hours of operation per county) were correlated with WIC participation but not with dental utilization and were used in our analysis.
The primary measure of oral health utilization was a 3-level variable defined as no visits, 1 visit, or 2 or more visits per year as represented by dental claims. These categories were used because the recommended number of dental visits is 2 per year.18 We did not distinguish among the number of visits greater than 2 per year because those differences are likely to depend on the severity of dental disease rather than basic issues associated with access to care. Because the measure of this dependent variable was coded as 0, 1, and 2, we used an ordered probit analysis with controls for clustering to examine WIC and oral health services utilization for each observation year (1 through 4).
We used separate random effects logit analyses (logistic regression) for each type of oral health services used. Type of services received was classified as (1) diagnostic/preventive services, (2) restorative services, and (3) emergency services. The American Dental Association procedure codes were used to classify service categories.18 Additionally, if a child had a hospital emergency room claim with a primary diagnosis of dental caries19 it was included as an emergency visit. These visit types were coded 0 or 1 to represent each type of visit per year as indicated by Medicaid claims.
Our major explanatory variable was childrens WIC participation measured as the number of months when any WIC voucher was redeemed during each year of life. We also incorporated relevant available sociodemographic control variables into our analysis. These included maternal educational level (years of school completed), maternal age (years), household income (actual dollar amounts), marital status (unmarried vs married), and minority status (non-White vs White). Many of these variables have been reported as important determinants of access to oral health care.2022 In addition, we used length of Medicaid enrollment (months) and dentists-to-population ratio in our analyses.
| RESULTS |
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| DISCUSSION |
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Our results also showed that young children participating in the WIC program are more likely to use preventive and restorative services and are less likely to use emergency services than WIC nonparticipants. These findings suggest that children participating in WIC may have a better connection to the health care system that can lead to care that is more planned and less urgent. If further studies can confirm a causal link between activities of a WIC nutritionist, dental referral, and use of dental services, it would appear that an important facet of the mission of WIC programsappropriate referrals to health and social servicesis being addressed. Our study contributes to the literature in 2 major ways: by broadening the understanding of the effects of WIC participation to oral health care and by making a methodological improvement on the way WIC effects are examined.
Methodological Contributions
Our study is the first to examine the WIC program and health services utilization with the 2-step statistical modeling approach. A strong criticism of previous WIC childrens health studies is their inability to control for the potential selection bias of enrollment in the WIC program.16 We conducted extensive tests for these sources of bias in the relation between WIC enrollment and use of oral health services and found that selection bias did exist. Random assignment of families to WIC participation would be a stronger design and would help overcome any selection bias. However, the practical problem of implementing this strategy in a community-based setting would be daunting, and such a design is not ethically defensible. To help control for selection bias, we used the 2-step methodology as described by Bollen et al.17 This approach makes a significant contribution to the literature about the WIC program because the majority of studies that examine the WIC program have been unsuccessful in recognizing and correcting for selection bias (endogeneity).16 Our study also demonstrates the feasibility of using 2-step analysis to control for selection bias when examining the effects of WIC on oral health care use.
Sporadic and continuously enrolled Medicaid children differ demographically, socially, and economically,23 so we did not limit the cohort to continuously enrolled children. Doing so would have biased the sample and threatened generalizability. Continuously enrolled children in our cohort had utilization rates for oral health services that were 3 times greater than those not enrolled continuously in Medicaid (30% vs 10%).24 Instead, we controlled for Medicaid enrollment with a variable for duration of months per year enrolled in the program. However this approach can create another bias because low-income children qualifying for Medicaid may receive dental care under private insurance, with fee for service, or at no cost during periods in which they are not enrolled in Medicaid. Although low-income children are likely to use medical care when not enrolled in public insurance programs, it is unlikely that they receive dental care, particularly young children in North Carolina, where excess demand for services exists and dentists participation in Medicaid is low.25 Furthermore, dental care is the most prevalent unmet need in uninsured children who are eligible for Medicaid.26 These findings underscore the difficulty young low-income children have in gaining access to oral health care regardless of insurance coverage.
Policy Contributions
In the policy area, we have several noteworthy findings. Our results indicate that childrens WIC participation has a significant and positive effect on oral health services utilization during the first 5 years of life. This finding is important because inadequate access to dental care is commonplace among children of families living in poverty. This situation has been documented in numerous national and state reports including those from the Office of the Inspector General,27 the American Dental Association,19 the General Accounting Office,28 the surgeon general,2 and the North Carolina Institute of Medicine.29
In the North Carolina Institute of Medicine report on access to dental care, it was reported that fewer than 13% of children aged 1 to 5 years received any dental services. Our findings indicated that WIC participation could increase to 23% the use of dental services for children at this age. This is an increase of almost 50% compared with findings of the North Carolina Institute of Medicine. Even with this rather dramatic percentage increase in use, the absolute utilization of 23% is still relatively low; more work needs to be done to address the access to dental care crisis among low-income young children. Medicaid alone is not enough to provide sufficient access to oral health care for young children, but when available in combination with another public health program such as WIC, access to oral care health can be greatly improved.
Limitations
These results should be considered in light of the studys limitations. First, we have a short study duration of 4 years (ages 1 through 4). For this reason, we chose the random effects model and not the fixed effects as suggested by Judge.30 The random effects model was able to control time-invariant variables as well as time-variant ones. We analyzed the child-level claims records and used panel data techniques that have not been applied in previous studies of WIC participation and use of services. Although we feel that we have made methodological improvements in the evaluation of WIC participation, future work should draw on additional years of panel data and address future questions such as the long-term oral health effects of the WIC program. In addition, because we examined the WIC program in only 1 state, this study needs to be replicated in other states. A single, expanded study with several states would involve considerable time and costs but could provide more generalizable and precise effects of the WIC program on access to oral health services.
We do not have information on childrens oral health status in the study. It is well documented that Medicaid children and children living in poverty have disproportionately more dental disease.31 Thus, any dental visit is likely to be beneficial to this high-risk population. The association of WIC with higher use of services may mean that oral health care needs of the children on Medicaid who participate in WIC are being better met. The findings for number of visits and type of use support this conclusion. Also, the adjusted odds of a child on Medicaid with WIC participation having 1 or more dental claims during the year was 1.3 to 1.5 times greater than that of a child with no WIC participation, across the 4 age groups. Studies have suggested that dental care is a serious unmet need among children in poverty, and our study suggests that use of dental care is enhanced among children participating in WIC services.
| Acknowledgments |
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The authors recognize Dr Paul Buescher, Stephanie Horton, and all the staff at the North Carolina State Center for Health Statistics for their help in obtaining the data and linkage. We also recognize Alice Lenihan and Sarah Roholt at the North Carolina WIC program for their assistance.
Human Participant Protection
No human subjects participated in this study. The protocol for this investigation was approved by the institutional review board at the University of North Carolina, Chapel Hill, School of Public Health.
| Footnotes |
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| References |
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2. Oral Health in America: A Report of the Surgeon General. Rockville, Md: National Institute of Dental and Craniofacial Research; 2000.
3. Early Intervention: Federal Investments Like WIC Can Produce Savings. Washington, DC: US General Accounting Office; 1992. Document HRD 9218.
4. Rush D, Horvitz DG, Seaver WB, et al. The National WIC Evaluation: evaluation of the Special Supplemental Food Program for Women, Infants, and Children, I: background and introduction. Am J Clin Nutr. 1988;48(suppl 2):389393.
5. Jones CM, Tinanoff N, Edelstein BL, et al. Creating partnerships for improving oral health of low-income children. J Public Health Dent. 2000;60:193196.[Web of Science][Medline]
6. Kennedy ET, Gershoff S. Effect of WIC supplemental feeding on hemoglobin and hematocrit of prenatal patients. J Am Diet Assoc. 1982;80:227230.[Web of Science][Medline]
7. Kotelchuck M, Schwartz JB, Anderka MT, Finison KS. WIC participation and pregnancy outcomes: Massachusetts Statewide Evaluation Project. Am J Public Health. 1984;74:10861092.
8. Kennedy ET, Kotelchuck M. The effect of WIC supplemental feeding on birth weight: a case-control analysis. Am J Clin Nutr. 1984;40:579585.
9. Schramm WF. WIC prenatal Participation and its relationship to newborn Medicaid costs in Missouri: a cost/benefit analysis. Am J Public Health. 1985;75:851857.
10. Rush D, Alvir JM, Kenny DA, Johnson SS, Horvitz DG. The National WIC Evaluation: evaluation of the Special Supplemental Food Program for Women, Infants, and Children, III: Historical study of pregnancy outcomes. Am J Clin Nutr. 1988;48(suppl 2):412428.
11. An Evaluation of the WIC program. Washington, DC: Institute of Medicine; 1990.
12. Kotch J. Assessing the Impact of WIC Program on Infants and Children. Final Report to the United States Department of Agriculture. Chapel Hill, NC: University of North Carolina at Chapel Hill; 1989.
13. Buescher PA, Horton SJ, Devaney BL, et al. Child participation in WIC: Medicaid costs and use of health care services. Am J Public Health. 2003;93:145150.
14. McCunniff MD, Damiano PC, Kanellis MJ, Levy SM. The impact of WIC dental screenings and referrals on utilization of dental services among low-income children. Pediatr Dent. 1998;20:181187.[Medline]
15. Sargent JD, Attar-Abate L, Meyers A, Moore L, Kocher-Ahern E. Referrals of participants in an urban WIC program to health and welfare services. Public Health Rep. 1992;107:173178.[Web of Science][Medline]
16. Besharov DJ, Germanis P. Rethinking WIC: An Evaluation of the Women, Infants and Children Program. Washington, DC: AEI Press; 2001.
17. Bollen KA, Guilkey DK, Mroz TA. Binary outcomes and endogenous explanatory variables: tests and solutions with an application to the demand for contraceptive use in Tunisia. Demography. 1995;32:111131.[Web of Science][Medline]
18. American Dental Association Web site. 2002. Available at: http://www.ada.org/prof/resources/pubs. Accessed February 2002.
19. International Classification of Diseases, 9th Revision. Geneva, Switzerland: World Health Organization; 1980.
20. Edelstein BL, Manski RJ, Moeller JF. Pediatric dental visits during 1996: an analysis of the federal Medical Expenditure Panel Survey. Pediatr Dent. 2000;22(1):1720.[Medline]
21. Hayward RA, Meetz HK, Shapiro MF, Freeman HE. Utilization of dental services: 1986 patterns and trends. J Public Health Dent. 1989;49:147152.[Web of Science][Medline]
22. Manning WG, Bailit HL, Benjamin B, Newhouse JP. The demand for dental care: evidence from a randomized trial in health insurance. J Am Dent Assoc. 1985;110:895902.[Abstract]
23. Davidoff AJ, Garrett AB, Makuc DM, Schirmer M. Medicaid-eligible children who dont enroll: health status, access to care, and implications for Medicaid enrollment. Inquiry. 2000;37:203218.[Web of Science][Medline]
24. Lee JY, Kotch J, Rozier RG, Vann WF. Dental care utilization by Medicaid children before five. Paper presented at: Face of a Child: US Surgeon Generals Conference on Oral Health; June 1314, 2000; Washington, DC.
25. Mayer ML, Stearns SC, Norton EC, Rozier RG. The effects of Medicaid expansions and reimbursement increases on dentists participation. Inquiry. 2000;37:3344.[Web of Science][Medline]
26. Newacheck PW, Hughes DC, Hung YY, Wong S, Stoddard JJ. The unmet health needs of Americas children. Pediatrics. 2000;105(4 pt 2):989997.
27. Childrens Dental Services Under Medicaid Program. Washington, DC: Office of Technology Assessment; 1990.
28. Childrens Dental Services Under the Medicaid Program. Washington, DC: US General Accounting Office; 2000.
29. North Carolina Institute of Medicine. Task Force Report on Dental Access. Raleigh, NC: North Carolina Institute of Medicine; 1999.
30. Judge C, Hill C, Griffith S, Lee T. The Theory and Practice of Econometrics. New York, NY: John Wiley and Sons; 1985.
31. Edelstein B. Policy issues in early childhood caries. Community Dent Oral Epidemiol. 1998;26(suppl 1):96103.[Web of Science][Medline]
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