The UCR is the oldest and most basic source of crime data. Collection was begun in 1930, and the FBI assumed administration of the reports in 1933. The information recorded derives from local police criminal incident records; currently, 13,000 reporting agencies contribute their data. 'Crime in the United States' is the annual publication in which these crime data are compiled; a quarterly release presents a breakdown of seven Index crimes according to population groups and geographic regions. UCR data can also be obtained by special request, which may take some time because most individual compilations are done manually. The UCR should not be used alone because it is a gross measure and not weighted for seriousness. Also, State data may differ from UCR data in timeliness and completeness. Two UCR counting schemes are used: violent crimes against persons are counted by victim, all others are counted by incident. Analysts should be aware of this UCR characteristic and recognize that combining robbery, for instance, with violent crimes will yield a result that represents a mixture of counting criteria. Furthermore, a counting hierarchy is observed, so that when a single incident is comprised of more that one offense, it is attributed only once -- and to the higher crime category. Finally, the UCR comprises only reported crimes and does not reflect the numbers of unreported incidents or statistics on arrest or disposition. A number of factors may bias use of the crime index, such as demographics which affect agency-to-agency comparisons. The crime rate is derived from the incidence per 100,000 population.