Patterns of Crime in Canadian Cities : A Multivariate Statistical Analysis
For the police and for other criminal justice agencies, it is important to understand the crime pattern of their own administrative areas in order to develop strategies and programs to control or prevent crimes. However, it is rather difficult to summarize a large amount of crime data to draw an individualized picture that portraits the crime pattern of an area such as a city. Each year, the Canadian Centre for Justice Statistics collects information, which are reported by all police departments across Canada, on more than one hundred crimes. Even if the data are grouped into 20 to 30 crime groups or crime categories, it is still rather difficult to describe the 20 to 30 crime rates in a concise way that can be easily understood. In addition, it is also important to make comparisons with other Canadian cities and crime rates for a specific city alone cannot provide such information. As a result, one common practice by police departments is to report the total violent crime rate and the total property crime rate and make a comparison with the overall Canadian crime rate (see an illustration in Appendix 1). This simplified picture is of course insufficient to represent the variety of individual offences such as assault, robbery or theft.
One alternate way to provide more information on crime data is to find out which kinds of crime correlate to each other. For example, statistical analysis shows that there is a high correlation between the following pairs of crimes, meaning that when the rate of one crime is high, the rate of the other crime is very likely to be also high:
- common sexual assault I and common non-sexual I
- common non-sexual assault I and major non-sexual assault II and III
- narcotics possession and fraud
For the 1999 data, the correlation coefficients of these three pairs are all above +0.7, meaning that these pairs of crimes usually occur together in the same cities. As a result, we can probably use common non-sexual I as an indicator for a list of crimes that closely correlate with it. However, as demonstrated in this study, there are better ways to represent the overall crime picture as well as to provide a comparison to other areas in the country.
The following statistical study attempts to delineate patterns of crime in Canadian cities by employing various multivariate statistical techniques. The objective was to represent crime patterns in cities by a small number of crime indices that can be easily understood and at the same time provide comparison among all Canadian cities. The study therefore is essentially a classificatory study, not an explanatory one.
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