Creating a complete and accurate accounting of the extent of sexual offending is challenging. First, there is no single defnition of sexual offending. Statutory defnitions of sex offenses differ from jurisdiction to jurisdiction; a sex crime committed in one state might not be classifed as a sex crime in an adjacent state. State laws differ on whether rape must involve physical force or threats of physical force, and so on. Even when using national standards, such as the categories reported by the 17,000 police departments submitting Uniform Crime Report (UCR) data to the Federal Bureau of Investigation (FBI), it is impossible for each offcer in each department to use the same exact criteria to decide how to classify a crime. Comparing recorded crime and victimization statistics is also challenging due to the variety of reference periods. UCR data are reported on a calendar year basis while National Crime Victimization Survey (NCVS) data, also completed annually, are compiled based on reports of victimization in the 12 months prior to the time of the interview. Comparing victimization data from different sources is even diffcult, as some sources measure lifetime victimization while others measure annual or college semester victimization. Finally, rate comparison can be problematic given the different ways in which the sample being studied is measured.