Certification Tools: NIBRS - UCR Comparisons

The UCR time series is THE history of crime for Connecticut agencies. Establishing whether the data are fundamentally comparable for the index crimes is central to building confidence in the NIBRS data among agency personnel. Also, when data are compared side-by-side for the same time frame, discrepancies usually appear and the reasons can be investigated. These investigations can lead to substantive changes in agency data gathering, thereby increasing the quality of the offense data.

A minimum of three months of UCR and NIBRS data are required, the same months for each system, for the initiation of the first certification analysis. After the initial analysis, which has always revealed discrepancies between the UCR and NIBRS data, additional months are needed to determine if the adjustments have corrected the problems.


The outcome of this analysis has consistently been very useful in uncovering errors in offense coding. The errors have been in both data sets - the UCR and the NIBRS offenses. Previously unknown UCR mistakes have emerged, as have incorrect assumptions about how the NIBRS offenses are to be coded. When an agency sees itself producing different crime numbers from the same data, they pay serious attention to resolving the differences. Clarifying and correcting these problems lead to both higher agency confidence in the NIBRS data and a greater sense of claiming the NIBRS system as their own.

Download Connecticut's UCR and IBR Comparison Agency Checklist (.doc)