Excerpt from the report: This report presents an analysis of invoice data from 15 major plants manufacturing skim milk products in the South Central area. Invoice data were for 1951 and included each sale by each plant in the study. The information obtained included date of sale, invoice price, quantity of product, basis for pricing, method of shipment, amount of transportation charges, type and location of buyer, and any premiums or discounts. A questionnaire was used to obtain additional data on pricing bases and other circumstances of the sale that could not be ascertained from the invoices.