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.

FNS published “The WIC Vendor Management Study, 1998” in July 2001 which examined, in part, the extent to which retail grocers, defined as WIC “vendors” were violating program rules and regulations. The 1998 study is a follow-up to the “WIC Vendor Issues Study, 1991” published by FNS in May 1993.