The comparability of data over time may be affected by industrial classification and geography changes.
Since 1998, SUSB has been tabulated based on the North American Industry Classification System (NAICS). Data were tabulated according to the Standard Industrial Classification (SIC) system for prior periods.
Classification changes are explored in detail in NAICS concordance reference files. In general, SUSB lags by one year the adoption of the classification system employed in the economic census.
Counties: County boundary changes are few and far between, but there were two introduced between the 2002 and 2003 SUSB: the creation of Broomfield County, CO, from parts of 4 counties, and the deletion of Clifton Forge (independent) city, VA, which was merged with Alleghany County. Such changes, detailed at /geo/www/tiger/ctychng.html, are implemented in SUSB in batches once every 5 years.Metropolitan and Micropolitan Areas (MSA's): Metropolitan areas are redefined after each population census and new criteria are generally introduced at that point.
In the 1998 - 2002 SUSB reports, corporate, subsidiary, and regional managing offices were tabulated in NAICS Sector 55. All other auxiliaries were tabulated in NAICS 95. Starting with the 2003 SUSB, corporate, subsidiary, and regional managing offices are still published in NAICS Sector 55, but the other auxiliaries are tabulated in the industry of the service performed. The other auxiliaries were coded into ten separate NAICS classifications listed in the auxiliary section of the 1997 .