The Special Supplemental Nutrition Program for Women, Infants, and Children program (WIC) is designed to provide food assistance and nutritional screening to low-income pregnant, postpartum women and their infants, and to low-income children up to the age of 5. The Supplemental Poverty Measure (SPM) is an alternative poverty measure produced by the Census Bureau since 2011 using the Current Population Survey Annual Social and Economic Supplement (CPS ASEC). Unlike the official poverty measure, the SPM incorporates in-kind transfer income from programs such as WIC, SNAP, and TANF. Past research suggests that survey responses to transfer program questions produce undercounts of both participation and total aggregate benefit amounts (Meyer and Mittag 2015, Shantz and Fox 2018, Mittag 2019). This underreporting can deteriorate data quality and potentially overestimate SPM poverty rates. To assess the impact of WIC misreporting on the SPM, this paper links state administrative data on the WIC program to the CPS ASEC covering calendar years 2009-2017. We use this linkage to directly compare self-reported WIC participation to the administrative data.
 
Overall, the CPS ASEC and the SPM procedure to estimate number of WIC recipients underreports participation when compared to the administrative records (5.0 percent vs 6.7 percent). About 41.5 percent who do report receiving WIC according to the administrative records do not report receiving WIC in the survey (false negative rate) while 1.2 percent who do report receiving WIC in the survey do not receive WIC according to the administrative records (false positive rate). Comparing the average annual benefit amount shows no difference between the survey and administrative data in our sample at the individual level which translates to a very small difference in overall Supplemental Poverty Measure rates; however, there are differences for some subgroups.