The Economic Census has been conducted every five years since 1967, and before that for 1954, 1958, and 1963. Prior to 1997, it was known as the Census of Manufactures. That same year, industries began being categorized according to the North American Industry Classification System (NAICS), which replaced the Standard Industrial Classification (SIC) codes used until 1992. Industrial concentration also is reported by the Economic Census on the basis of value added. Industry concentration ratios and HHIs for the 1992 and 1997 economic censuses can be accessed online at: http://www.census.gov/epcd/www/concentration.html. Information on industrial concentration is not readily available for sectors of the economy other than manufacturing.