Linking WIC program and HMO administrative data to study the impact of WIC participation

Background: The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) serves lowincome women and children up to age five in the U.S. While numerous studies document the health impacts of WIC participation, these studies often lack adequate control groups of families eligible for WIC but not participating. This study sought to link a large WIC administrative dataset with electronic health records from a Health Maintenance Organization (HMO) with the goal of supporting rigorous evaluations of the impact of WIC on child health outcomes beyond the age of five. Methods: Children's WIC-eligibility status was determined by Medicaid status. Since no common unique identifier existed, we linked WIC and HMO child records using child's first and last names, date of birth, sex, and address history using exact and fuzzy matching based on sound and the edit distance between two alphanumeric strings. A fuzzy-match score quantified uncertainty. All analysis was conducted by WIC research staff; no identifying information about WIC participants was exchanged. Participants: Los Angeles County children seen at an HMO (n = 974,451) between 2008 and 2016 and children enrolled in WIC between 2003 and 2018. Results: 17.3% of HMO children definitely matched a WIC-participating child, 12% possibly matched, 14.3% were eligible but did not match a WIC-participating child and 56.4% were not WIC eligible. Conclusions: With appropriate data confidentiality safeguards in place, linking administrative datasets from federal programs with electronic health records is a cost-efficient way to identify a viable comparison group necessary to document the impact of government investments.