The representative sample of 3,024 police and sheriff's departments was composed of four divisions grouped by area type:

• All police departments serving cities with populations of more than 25,000 (large cities).

• A randomly selected sample of police departments serving cities with populations between 2,500 and 25,000 (small cities).

• All suburban county police and sheriff's departments (suburban counties).

• A randomly selected sample of rural county police and sheriff's departments (rural counties).

The entire universe of large cities (1,216) and suburban counties (664) was included in the representative sample for two reasons. First, the 1995 National Youth Gang Survey revealed that gang activity in the United States is positively correlated with large populations. Second, a great deal of research on gangs has been conducted for large population areas. The 1996 National Youth Gang Survey permits comparative analysis with samples from previous surveys.

The random samples of small cities and rural counties were selected using a formula developed by Cochran (1977, see Appendix C). Implementation of the sampling method produced the following sample sizes: 399 jurisdictions from a total of 8,740 cities with populations between 2,500 and 25,000 identified by the U.S. Department of Commerce, Bureau of the Census³ and 745 rural counties from a total of 2,356 included in the Federal Bureau of Investigation's Crime in the United States, 1994: Uniform Crime Reports (Federal Bureau of Investigation, 1995).

The comparative sample of 1,956 police and sheriff's departments comprised jurisdictions that were surveyed in 1995 but not included in the 1996 representative sample. These jurisdictions will be surveyed in future years for the purpose of evaluating trends in gang activity.

Survey instructions specifically asked sheriff's departments to report only for their "unincorporated service area and any contracted jurisdictions." This was done in an effort to avoid sheriff's departments reporting for cities and towns within their counties that were already in the survey sample. In a few instances, county agencies did not follow survey instructions, but these instances of duplicate reporting were corrected in the course of preparing the data for analysis.

All jurisdictions included in the sample were cross-referenced with a U.S. Department of Commerce, Bureau of the Census database so that accurate and current populations could be assigned to each. Jurisdictions were linked to a Federal Information Processing Standards (FIPS) Code, which is administered by the U.S. Office of Management and Budget. Each FIPS Code is unique and is linked to the most recent Bureau of the Census population estimates. This survey used estimates for 1994 because these were the most current population estimates at the time the sample was developed.

Each city and town was assigned a FIPS Code that corresponded to the entire population of that area.⁴ Counties were assigned populations for their unincorporated areas. FIPS Code language refers to the unincorporated area of a county as the "balance of" a county. This figure excludes the populations of incorporated cities and towns within the county. A few counties do not have a "balance of" population because there are no cities or towns within the jurisdiction. In such cases, the jurisdiction was assigned the population of the entire county.