10.6 Offence category; Charge category

The method used in this report for categorising an offender management episode by offence category is similar to a method commonly used by the Ministry of Justice. For each episode of management only offences relating to that episode are considered. Thus, for recalled offenders this includes the offences they are recalled upon as well as any new offences. The most serious offence is selected according to the Ministry of Justice seriousness score. The most serious offence is then mapped to a descriptive offence category.

The Ministry of Justice offence seriousness score is described below:

"A seriousness of offence scale was originally developed by the Policy and Research Division of the Department of Justice in 1991, and has been updated about every five years since then. The most recent update of the scale occurred in February 2005 by the Ministry of Justice. The updated scale gives imprisonable offences a score according to how serious judges have deemed each offence in terms of the use of custodial sentences over a specific time period.

The updated scale is based on court sentencing data for the period 2000 to 2004. The seriousness score assigned to each offence is the average number of days of imprisonment imposed on every offender convicted of that offence between 2000 and 2004, where the average is taken over both imprisoned and non-imprisoned offenders. Suppose, for example, that between 2000 and 2004 there were 100 cases of offenders convicted of a particular offence. Of these cases, 50 resulted in a custodial sentence, and the average length of the custodial sentences imposed on these offenders was 30 days. The seriousness score for this offence is (30 x 50/100), or 15.

Offences that became obsolete prior to 2000 were given the same score as any new similar offences, or a score was calculated based on sentencing data before 2000. Imprisonable offences for which there were convictions but no custodial sentences over the period 2000 to 2004, were given a seriousness rating slightly lower than the least of the offences already assigned a seriousness score (i.e. a score of 0.2). Non-imprisonable offences were assigned a seriousness score of zero"

Police offence codes and descriptions have been assigned to offence categories and can be inspected in detail here along with their associated Ministry of Justice seriousness scores. The categories used here are particular to this document but related to the Police offence code groupings. Some extra groupings are used here to assist in illustrating particular trends or relationships. For instance the age profiles for offenders grouped by "Homicides", "Assaults, abduction, threats" or "Robbery" are distinctly different so they have not all been grouped together as "Violence".

The table below gives general descriptions of the offence categories used in this report.