An Introduction to the Crime Severity Index

Every year, Statistics Canada reports on the number and type of criminal offences that come to the attention of police. These offences are reported at the national, provincial, and census metropolitan area level as a rate per 100,000 population. Expressed in this way, the volume of criminal incidents can be compared across any number of geographic areas. In computing this rate, all offence types included in the study are awarded the same degree of seriousness. As such, despite differences in the severity of many offence types over others, such as homicide and mischief for example, all police-reported criminal incidents are counted as equal units in the calculation of the crime rate.

In 2009, Statistics Canada unveiled a new analytical tool for measuring crime in Canada: The Crime Severity Index. In measuring the volume of crime across Canada, this tool also accounts for the varying degrees of severity that exist between offence types by weighting each according to a scale of seriousness. To this end, the Index allows crime trends to be analyzed and compared according to the gravity of the offences that were brought to the attention of police.

This new tool addresses some of the limitations of the traditional crime rate. The traditional crime rate has been susceptible to fluctuations in the number of high-volume but low-severity offences, such as mischief and theft under $5000. These offences account for 40% of all police reported crime in Canada. Victimization data has shown that offences of lower seriousness tend to go unreported to police. Individual police services may also practice certain policies that promote reporting among victims of crime. Both under-reporting and pro-reporting policies can directly influence the number of crimes reported to police from year to year. In turn, low-severity offences are not always reported consistently by police to Statistics Canada. This impacts the comparability of the traditional crime rate between jurisdictions and can actually conceal significant changes in the numbers of severe crimes like assault and murder by masking them among low-severity crimes.

The impetus behind the Crime Severity Index was to develop an indicator by which the types of crimes occurring in Canada could be analyzed in terms of their relative seriousness, thus complementing a more simple volumetric assessment. As a result, this would reduce the impact that high-volume, less-serious offences have on the crime rate as fluctuations in the Index would be indicative of changes in the severity of crime. The Index would also minimize the impact that differences in police reporting practices can have on the crime rate. In the end, the Index would improve the comparison capabilities of crime data among provinces and municipalities.

The weighting system used to assign levels of seriousness to each offence was designed by incorporating the logic of conventional sentencing practices used in actual criminal courts. A review of the data collected by Statistics Canada's surveys of adult and youth criminal courts shows that sentencing decisions are a reflection of the severity of the offence. That is, more serious offences will render more serious punishments. Sentences were assessed in terms of both the incarceration rate and the average length of imprisonment for each individual offence type. The weight of each offence was developed in accordance with this relative sentencing principle. The more serious the crime, the higher the weight the offence was assigned on the Index scale. The Index was standardized to 100 for Canada using 2006 as its base year.

Comparisons between the overall crime rate and the Crime Severity Index demonstrate the utility in analyzing crime trends with both tools. Between 1999 and 2002, there was virtually no change reported in Canada's overall crime rate. Meanwhile, the Crime Severity Index decreased by 6%. Further investigation showed that while there was a large increase in the number of reported mischief offences, the number of robberies and break-ins dropped substantially. In this case, the Crime Severity Index was able to capture a significant shift in crime patterns that would not have been evident with a simple assessment of the crime rate. More recently, in 2009, the Crime Severity index dropped 4% from 2008, while the crime rate dropped 3%.