For instance, when the size of a police force increases, changes in the perceived likelihood a crime will be solved may result in a higher fraction of victimization to be reported to the police. Three data sets are used to measure the magnitude of this reporting bias. While the analyses are subject to individual criticisms, all yield similar estimates. Reporting bias appears to be present but relatively small in magnitude, and each additional police officer is associated with an increase of roughly five index crimes that would have previously gone unreported. Taking reporting bias into account makes the hiring of additional police officers substantially more attractive from a cost-benefit perspective but cannot explain the frequent inability of past studies to identify systematic negative relationships between police force size and crime rates. Study data also indicate that the propensity of victims to report crimes to the police has changed little since 1973 but that the gap between victim claims of crimes reported to the police and the number of crimes officially recorded has steadily decreased. Implications of the findings for the use of Uniform Crime Reports are considered. 44 references and 5 tables