Handbook of Methods

Classification Systems

Definition

Classification systems are ways of grouping and organizing data so that they may be compared with other data. The type of classification system used will depend on what the data are intended to measure. Some datasets may use multiple classification systems.

Examples of classification systems

Geography. Political boundaries such as country, state, and county lines tend to be fixed and don’t change over time. Cities and metropolitan areas tend to be classified by population and commuting patterns observed in the decennial census.

For some of the metropolitan area definitions in use at BLS, see

• Census metropolitan and micropolitan area definitions
• New England City and Town Areas (NECTA)

For geographic area information by program, see

• Current Employment Statistics geographic area definitions
• Occupational Employment Statistics geographic area definitions
• Local Area Unemployment Statistics area definitions
• Quarterly Census of Employment and Wages area definitions
• Consumer Price Index areas measured
• Consumer Expenditure Survey area definitions
• Survey of Occupational Injury and Illness area definitions
• Census of Fatal Occupational Injuries and Illnesses areas

Industry. Surveys of businesses use industry classification systems to classify businesses by their activity, or production process. The classification system in use for most BLS programs that collect industry data is the North American Industry Classification System (NAICS).  Prior to NAICS, BLS used the Standard Industry Classification (SIC) system.

For more information on these classification systems, see

• North American Industry Classification System (NAICS)
• Standard Industrial Classification (SIC) system
• International Standard Industrial Classification (ISIC) system

Occupation. Occupational classification systems group workers by the duties they perform. The occupational classification system in use for BLS programs is the Standard Occupational Classification (SOC) system.

For more information on the SOC, see

• Standard Occupational Classification (SOC) system

Commodity. Commodity classification systems group products together.

For more information on these classification systems, see

• End-use classification system