Benchmarking is a standard or point of reference by which data can be compared. BLS fields many surveys, which are subject to sampling error (See error measurement topic.) Some surveys are able to compare their survey estimates with censuses or more comprehensive sets of data.
The Current Employment Statistics (CES) survey surveys approximately 588,000 worksites each month. This survey is very large, collecting data on about 32 percent of total nonfarm employment each month from a stratified probability sample of about 6 percent of the 9.5 million records that the Quarterly Census of Employment and Wages (QCEW) collects on a quarterly basis.
Each year, the national CES benchmarks the March employment level to the first quarter employment level of the QCEW. This process of aligning the sample estimate (CES) with the universe estimate (QCEW) is known as benchmarking.