Standard industrial classification codes have been replaced in the 1997 Census of Agriculture by the new North American Industry Classification System (NAICS). NAICS is a unique, all-new system for classifying business establishments. It is the first economic classification system to be constructed based on a single economic concept. Economic units that use like processes to produce goods or services are grouped together. In the case of the Census of Agriculture, the shift from SIC codes to NAICS codes involves few changes. Farms are grouped into crop or livestock production and then into the subcategory which accounts for 50% or more of the total value of sales of agricultural products (i.e., cotton, tobacco, dairy).