How are producers and products selected for the PPI survey?
PPIs are published for the output of virtually all U.S. mining and manufacturing industries and are gradually being introduced for the output of industries in other sectors of the economy. For any given industry, producers are selected for the survey via a systematic sampling from a listing of all firms that file with the Unemployment Insurance System. Typically, a firm’s probability of selection is based on its employment size. After a firm is selected and agrees to participate in the survey, a probability sampling technique called disaggregation is used to determine which specific products or services will be in the PPI. Disaggregation is a process in which iterative steps are taken to select items based on their proportionate value to the manufacturer’s overall revenue. First a reporter breaks down the type of items shipped into categories. Next, these categories are broken down further by price determining characteristics, for example, options, color, size. Further break downs may
