The reliability of police employee counts: Comparing FBI and ICMA data, 1954–2008

Researchers commonly use secondary data counts of police employees from police agencies. There has been some concern with using such data, yet there have been no published systematic assessments of their reliability.PurposeThis paper compares the reliability of annual counts of police officers and civilians from the FBI's Police Employees data to those in the International City/County Management Association's (ICMA) Municipal Year Book reported for 38 large city police agencies between 1954 and 2008.MethodsWe use bivariate correlations and visual analyses of line charts to demonstrate the reliability of these two datasets, examining in particular situations in which inaccuracies emerged.ResultsOverall, both data sets record accurate counts of police employees, but there is some evidence of reporting irregularities. These irregularities manifest themselves as either city/agency-specific or temporally-bounded reporting errors.ConclusionsAlthough reporting errors are rare in these data, future researchers should consider the potential impact of reporting errors for certain years and agencies.

► We systematically assess FBI and ICMA counts of police employees in 38 US cities.
► For most cities we find high levels of reliability between the two data sources.
► There is some evidence of reporting irregularities in specific cities.
► Usually reporting errors are temporally bounded.