The data are compiled from the U.S. Census Bureau’s annual surveys of governmental finances and employment. The justice data include the expenditures and employment of the Federal Government, the State governments, and a sample of county, municipal, and township governments.  Unless otherwise noted, data for total governmental expenditures, including justice and non-justice governmental functions, also include the expenditures of special districts and school districts, which generally do not have justice functions.

The most recent survey sample was selected from the 2002 Census of Local Governments and consists of large units of government (including all 50 States) sampled with certainty and smaller units selected with a probability proportional to the unit’s expenditure.   It was designed to produce state by type of government estimates with a relative standard error of 3 percent or less for total expenditure and state estimates with a relative standard error of 5 percent or less on total expenditure, criminal justice, and other government functions. All other government units were selected into the sample with a probability proportional to their size.

The sampling parameters have changed over time, but only for the Finance portion.  In the years 2001 and 2003 the sample size was halved.  The estimates on a state by state level based on the as the modified sample design wouldn't support analyses.  The 2004 sample reverted back to the same methods as the 2000 sample.