Convergence Revisited: A Multi-Definition, Multi-Method Analysis of the UCR and the NCVS Crime Series (1973-2008)

Inter-study discrepancies in the length of available time series, definition of convergence, rate calculation adjustment, and application of statistical techniques have contributed to confusions in understanding the relationship between the uniform crime reports (UCR) and the national crime victimization survey (NCVS). This study tests and compares the outcomes of UCR-NCVS crime rate convergence in a 36-year time series (1973-2008) using multiple definitions and an assortment of methods. With adjusted crime rates, our graphic analysis shows strong evidence of convergence between the two series in all crime categories. High correlation coefficients (.80+) are obtained in Robbery, Burglary and MV Theft categories using nondetrended data and the full 36-year time series. Split-series correlation analyses based on 18 equal-sized (half) series yield not only very high coefficients (.90+) in the more recent split-series but also a clear pattern in support of the UCR-NCVS convergence (as "correlated rates") conclusion in all crime categories examined. Similarly, rate deviation regression analyses confirm that the differences between the UCR and the NCVS crime rates in all tested categories are decreasing significantly over time and that the two crime series are in the process of converging. Outcomes derived from the Engle-Granger test of cointegration, in contrast, are the most modest, indicating that the two crime series have only cointegrated in the Burglary category. We suggest that conclusions on the UCR-NCVS convergence are partly contingent on the definitional and methodological contexts. Convergence studies should be conducted periodically not only to monitor the validity of the dual national crime measures but also to identify questions deserving attentions from both researchers and policy- makers.