As part of the NAICS implementation process establishment employment data* based on the NAICS structure will be available from 1990 forward. This time series was based on the Longitudinal Database - a national database of all Covered Employers. The advantage of using the Longitudinal Database for the data reconstruction was the availability of actual micro data which kept industry codes constant over time thereby eliminating coding errors and corrections. Conversely, holding the NAICS code constant over time also eliminated any true economic changes that may have occurred over the ten-year period. Therefore, this time series provides data that is more historic than economic in nature