- Developed in the 1930s, the Standard Industrial Classification (SIC) code is a 4-digit scheme that organizes 1,004 industries. Some 400 of these are services.
- Developed in 1997, the North American Industrial Classification System (NAICS), is a six-digit scheme that organizes 1,170 industries, of which 565 are services. Many of the NAICS industries emerged over the past 20 years.
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