Weighted Crosswalks for NAICS and SIC Industry Codes

We provide weighted crosswalk files for the purpose of bridging Standard Industrial Classification (SIC) codes and North American Industry Classification System (NAICS) codes. SIC codes were the standard industry classification system for decades, but they eventually couldn’t keep up with the changing industrial structure of the 1990s. NAICS codes took over in 1997 and quickly became the reporting system for most government statistics in the US and elsewhere. This switch (and subsequent NAICS updating) poses a problem for researchers since it imposes an artificial break in time series data. Unweighted crosswalk tables can help connect the two systems, but the many splits and merges create mappings that are not one-to-one. For situations that require one-to-one translations, researchers find themselves guessing as to the best match. And for situations where splitting and merging is acceptable, choosing weights sometimes feels arbitrary. The crosswalks included here contain weighting variables that make it possible to smoothly bridge between systems and all NAICS updates in a nonarbitrary way. Three different weighting schemes are included. The first based on employment, the second based on number of establishments, and the third based on total payroll. NOTE THE MAJOR EXPANSION/UPDATE IN JULY 2025. USE LATEST VERSION!