When looking for Industry Ratios it is important to know about and use the SIC/NAICS codes. The Standard Industrial Classification (SIC) and North American Industry Classification System (NAICS) are numerical classification systems created by the United States government to identify lines of business. If you know the industry code, you can easily identify your industry's ratios within each of the recommended resources listed below. While NAICS has "officially" replaced SIC, many business directories and databases still use one or both of the systems. Therefore, it is important to know about both SIC and NAICS.