98991114_rime_in_the_United_States_2006__Reason_for_Estimation
[Year] 1991 [State(s)] Illinois [Estimation Method] The rape totals were estimated using national rates per 100,000 inhabitants within the eight population groups and assigning the forcible rape volumes proportionally to the state. [Reason for Estimation] 
The state UCR Program was unable to provide forcible rape figures in accordance with UCR guidelines.
Table 01, Data Declaration - Crime in the United States 2006
Reason for Estimation