This report provides improper payment estimates for fiscal year 2011 using a methodology for “aging” the 2005 bookend study. The methodology yields nationally representative estimates of the number of vendors that over- and undercharged and the amount of over- and undercharges across all WIC vendors.

In 1991 and 1998, FNS conducted national studies of WIC vendors to determine the extent of vendor violation of program rules. After the 1998 study, FNS issued regulations to correct vendor practices. The 2005 study replicates the 1998 study to determine whether the regulations were effective, and to measure the frequency of vendor violations and the degree to which vendors charge accurate prices for WIC transactions.