Comparisons between different countries

Differences in definitions of violent crime make international comparisons problematic, and account for at least some of the apparent differences in recorded violent crime rates between countries.

Definitions of offences vary between countries due to both legal differences and statistical recording methods. For example, the USA and Canada do not appear to include minor assaults, intimidation, and threats within their definition of violent crime. However, New Zealand does include these crimes in its definition, and these offences comprise approximately half of all violent crime in this country. Also, New Zealand does not include sexual offences in violent crime, whereas Australia, USA, Canada, England and Wales do.

Besides definitional differences, recorded crime figures are likely to be affected by many other factors including:

• Rates at which crimes are reported to, and recorded by, the police. For example, the 2000 International Crime Victims Survey of seventeen countries (not including New Zealand) indicated that from country to country the percentage of robbery offences reported to the police ranged from approximately 30 to 75 percent; assaults with force ranged from approximately 15 to 70 percent; threats ranged from approximately 20 to 55 percent; and reporting rates for sexual assaults ranged from approximately 28 to 65 percent. In the 1996 New Zealand National Survey of Crime Victims, it was estimated that 23.6 percent of robberies, 32.8 percent of non-domestic assaults, and 18.5 percent of non-domestic threats were reported to the Police. It should also be noted, however, that comparisons drawn between different countries' crime surveys may be of limited use due to factors such as differences in survey design, coverage, response rates, methodology for data collection and offence definitions;

• Differences in the point at which crime is recorded. Generally, crime appears to be recorded when preliminary investigations provide sufficient evidence that an offence has been committed. Some countries record crime, however, when the offence is reported to the police, while other countries may not record a crime until a suspect is identified and papers are forwarded to the prosecutor;

• Differences in the rules when counting multiple offences by individuals. For example, in New Zealand, recorded crime data indicates one count for every offence recorded, regardless of how many were committed by the same individual. In some countries multiple crimes of the same type, occurring within the same incident may be recorded as one crime, depending on the type of crime;

• Whether crime rates are counted in terms of the number of offences, or the number of victims. In New Zealand, all offences arising from a single incident or in relation to a single victim are normally counted. In contrast, in some other jurisdictions there are "hierarchy rules" so that only the most serious offence is counted;

• Changes in data quality over time; and 

• The population standards used to calculate crime rates per capita. Some countries employ adult populations in these calculations, while others use total population. When the total population is used, the resulting crime rate per capita is lower than when adult population figures are employed. 

It is strongly recommended that these issues be reported along with any comparisons drawn between different countries' violent crime rates.