摘要：Objectives. We used a geographic information system and cluster analyses to determine locations in need of enhanced Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) Program services. Methods. We linked documented births in the 2010 California Birth Statistical Master File with the 2010 data from the WIC Integrated Statewide Information System. Analyses focused on the density of pregnant women who were eligible for but not receiving WIC services in California’s 7049 census tracts. We used incremental spatial autocorrelation and hot spot analyses to identify clusters of WIC-eligible nonparticipants. Results. We detected clusters of census tracts with higher-than-expected densities, compared with the state mean density of WIC-eligible nonparticipants, in 21 of 58 (36.2%) California counties ( P < .05). In subsequent county-level analyses, we located neighborhood-level clusters of higher-than-expected densities of eligible nonparticipants in Sacramento, San Francisco, Fresno, and Los Angeles Counties ( P < .05). Conclusions. Hot spot analyses provided a rigorous and objective approach to determine the locations of statistically significant clusters of WIC-eligible nonparticipants. Results helped inform WIC program and funding decisions, including the opening of new WIC centers, and offered a novel approach for targeting public health services. The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), a federally funded nutrition and health program, was established as a pilot program in 1972. 1 WIC provides nutrition education, referrals, breastfeeding support, and nutritious supplemental food for low- to moderate-income families with nutritionally at-risk pregnant and breastfeeding women, infants, and children up to the 5th birthday. 1,2 With an annual federal budget of $6.2 billion, the WIC program serves nearly 9 million participants each month through 1900 local agencies in state public health departments, Indian tribal organizations, and US territories. 1,2 Additionally, the WIC Overseas Program provides services to Americans and dependents living overseas at US military bases. Nearly 30% of pregnant women participate in the WIC program nationally each year. 2 In 2010, the WIC program served 62.6% of all who were eligible. WIC served 84.8% of eligible infants, 80.6% of eligible postpartum women (both breastfeeding and nonbreastfeeding), and 52.4% of eligible children aged 1 to 4 years. 3 In California, WIC agencies provide services to nearly 1.45 million women, infants, and children each month at more than 625 sites statewide with an annual budget of approximately $1.2 billion. 4 Research focused on the prenatal benefits of the WIC program has not produced consistent conclusions. 5 Some research has indicated that WIC participation is associated with improved birth outcomes 6 and that provision of WIC services to pregnant women reduced low birth weights (< 2500 g) and very low birth weights (< 1500 g) by 30% and 54%, respectively, with substantial reductions in first-year medical costs for US infants. 7 Moreover, prenatal WIC participation was found to reduce racial disparities in infant mortality rates. For example, the infant mortality rate for African Americans was significantly lower for WIC participants than for non–WIC participants. 8 However, other studies have indicated that prenatal participation in WIC had minimal effects on adverse birth outcomes. 9,10 Not all women and children who are eligible to receive WIC services actually participate in the program. 11 In 2007, only 59% of the total eligible US population participated in the program. 12 Research has demonstrated that significantly higher rates of enrollment were observed for women who received prenatal care at health department– and community-sponsored clinics compared with hospital clinics and private physician offices. 13 The number of prenatal visits was found to be positively associated with WIC participation rates among pregnant women, 13 and the number of prenatal visits was found to improve birth outcomes. Previous participation in the WIC program was positively associated with early prenatal enrollment in WIC. 14 Spatial analytical methods and geographic information systems (GISs) have increasingly been used in public health, epidemiology, and nutrition research. 15–17 Nutrition researchers have begun to recognize the importance of GIS and spatial analysis, particularly as they relate to measuring the role of the built environment 18 and the food environment. 19 GIS and nonstatistical (i.e., descriptive) mapping techniques have recently been used to explore disparities in access to fresh produce in low-income neighborhoods. 20 We are unaware of any studies, however, that have used statistically based spatial analyses to assess WIC-eligible women who were not participating in WIC services. Hot spot analysis is a statistically based method to assess geographic clustering. Specifically, hot spot analysis is used to pinpoint locations of statistically significant high- and low-value clusters of a phenomenon of interest by evaluating each feature (e.g., census tract) within the context of neighboring features and against all features in the dataset. 21 A feature with a high value may be a statistically significant hot spot if it is also surrounded by other features with high values, as opposed to simply being a data outlier. The local mean for a feature and its neighbors is compared proportionally with the global mean of all features (e.g., all census tracts in a state). When the observed local mean is much different than the global mean and that difference is too large to be the result of random chance, a statistically significant z score results and a hot spot cluster is detected. 22 Recent studies using this technique have explored factors associated with West Nile virus incidence, 23 tuberculosis transmission, 24 patterns of sexually transmitted diseases, 25 locations of health care services, 26 and community-level overweight and obesity. 27 The purpose of our study was to identify the macro- and microlevel geographic regions of California that contain clusters of WIC-eligible nonparticipants. Findings were intended to provide the California WIC Program with an evidence base for funds allocation, to inform program decisions for a subset of counties and subcounty areas, and to strategically target specific populations and areas for WIC service enhancements (i.e., opening of new WIC centers).
