The correspondence or divergence of the UCR and the NCVS takes on extra importance when there appears to be a shift in long-term crime trends. Between 1992 and 2004 the United States experienced a long period of declining crime, by both measures. More recently there have been signs of an upturn in crime in a number of cities, and the national crime rate as measured by the UCR has increased in two consecutive years. It is precisely at turning points such as the current one that rich and timely measures of a variety of aspects of crime are required, to better understand the trajectory that the nation seems to be taking.
Although the UCR and NCVS estimates of the number of serious violent crimes reported to the police have generally become more similar over the past decade, this convergence in levels is not yet fully understood, nor is it clear whether the similarities in estimates will continue in the future (see Lynch and Addington, 2007). This is because the convergence in the estimates does not necessarily reflect a reduction in error by one or both series. Rather, the two series can produce different estimates and varying long- and short-term trends because they measure different aspects of the crime problem using dissimilar procedures. Furthermore, even if the convergence does reflect some reduction in error associated with one or both series, there is little evidence to suggest that this pattern will remain constant in the future.
As evident in Figure 3-2, annual estimates of the total number of serious violent crimes derived from NCVS data have often been higher than the annual counts in the UCR. There are several reasons why this may occur. Most importantly, the NCVS data include crimes that are not reported to the police. Approximately 49 percent of violent victimizations and 36 percent of property victimizations are reported to the police (Hart and Rennison, 2003). In addition, NCVS counts may be higher if police departments do not record all of the incidents that come to their attention or do not forward the reports to the national UCR program.
For some types of crimes in the NCVS and the UCR, it is possible to reconcile apparent discrepancies in annual estimates by adjusting the NCVS counts to include only those incidents said to have been reported to the police. When such adjustments are made, levels and trends in burglary, robbery, and motor vehicle theft appear generally similar in the NCVS and UCR. However, UCR and NCVS levels and trends in serious violent crime, such as aggravated assault and rape, exhibit many discrepancies after these kinds of adjustments are made. These differences in both levels and trends in aggravated assault and rape may result from changes concerning the public’s willingness to report crime to the police, changes in the way police departments record crime, or some other factor. It is clear that the differences in the methodologies of the UCR and NCVS programs must be considered when assessing both levels and trends of crime in the nation. However, the fact that the extent of agreement in current levels of crimes depends on the