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NATIONAL OFFENCE INDEX - TECHNICAL PAPER
3 As part of the quality improvement processes for the representation of offence information in crime and justice collections, the National Centre for Crime and Justice Statistics (NCCJS) has developed a National Offence Index (NOI). The NOI is a ranking of offence categories of the Australian Standard Offence Classification (ASOC) according to their level of seriousness. The ASOC was used to ensure that offence statistics were reported according to a standard classification. This overcomes different ways of categorising offence information across the states and territories reflecting their different legislative frameworks.
4 The purpose of the NOI is to enable the representation of a defendant by a single offence. Therefore, where a defendant has two or more offences in different output offence categories (for this publication the output offence category is the ASOC division) the most serious offence is chosen to represent that defendant. For the purposes of this publication, categorisation by a single principal offence provides an important and useful way of understanding the types of criminal cases finalised in the Magistrates' and Higher Criminal Courts. It also provides a mechanism for associating offence information with a range of data variables linked to the defendant.
NATIONAL OFFENCE INDEX (NOI) DEVELOPMENT
5 The NOI is based on the Offence Seriousness Index developed by the Crime Research Centre (CRC) in Western Australia. The CRC Index was developed using two methodologies: research on public perception of offence seriousness and consideration of legislated sentences. The Index was developed in 1991, and subsequently reviewed in 1998 following the introduction of the ASOC. The review in 1998 ranked all ASOC groups (4 digit codes), though no supplementary codes were included. The ABS has used the 1998 version of the CRC Index as a base Index for the NOI.
6 Evaluation of the CRC Index was conducted utilising data from the ABS' Higher Criminal Courts collection for the period 1 July 2000 to 30 June 2001. Data on the most serious offence using the CRC Index was compared with the ABS' principal offence data from this collection. All adjudicated offences were mapped to the ASOC. The Principal Offence Rules determined principal offence based on severity of sentences handed down to defendants (sentence type followed by sentence quantum).
7 The results indicated that the output from the two methods were similar, with the most notable differences occurring in the ASOC divisions: 2-Acts intended to cause injury; 6-Robbery, extortion and related offences; 7-Unlawful entry with intent; 8-Theft and related offences; and, 10-Illicit drug and related offences. Also, the proportion of defendants for whom principal offence could not be determined, although lower than that using the principal offence rules (national average of 17%), was still quite high (national average of 12%). The main explanation for the figure of 12% was that offence information in the Higher Criminal Courts collection included supplementary ASOC codes (i.e. division and subdivision codes). These codes were not included in the CRC Index and therefore were unable to be ranked and subsequently the defendant was unable to be allocated a principal offence.
8 The analyses above indicated two key areas to be investigated further:
9 An analysis of co-occurring ASOC divisions was conducted. This analysis indicated that the ASOC divisions most likely to co-occur were the same ASOC divisions indicated in paragraph 7 above. Therefore, for offences that most often co-occur it is more likely that there will be differences in their selection as a principal offence using the Principal Offence Rules versus the CRC Index. Following this analysis and consultation with the practitioner and advisory groups in crime, courts and corrections, changes were made to the ranking of selected offences. These changes were:
10 Separate analysis of the offence data in the Higher Criminal Courts collection for 2000-01 indicated that around 10% of all adjudicated offences for adjudicated defendants had supplementary ASOC codes that were not included in the CRC Index. In developing the NOI, these ASOC codes were allocated an Index ranking where possible. There were three scenarios for this:
11 The inclusion of selected ASOC supplementary codes reduced the national proportion of adjudicated offences for adjudicated defendants unable to be ranked from around 10% to less than 2%.
12 The NOI was used to produce principal offence output from the 2000-01 Higher Criminal Courts collection, which was then compared with the principal offence output produced using the Principal Offence Rules. The analysis indicated:
13 The application of the NOI is simple compared with the Principal Offence Rules as the NOI only requires valid ASOC codes, whilst the Principal Offence Rules require valid ASOC codes, sentence type and sentence quantum. In addition, the NOI is more robust because it deals with situations such as global sentencing (a single sentence given for multiple offences), which has a large impact on the output in some States and Territories. Added to this, there is scope for greater usage due to decreased burden on data providers, and usage can extend across police, courts and corrections agencies as the NOI does not require sentencing information.
APPLICATION OF THE NATIONAL OFFENCE INDEX
14 The NOI has been used to produce the principal offence information in this publication for the defendants finalised by adjudication in the Higher Criminal Courts and Magistrates' Criminal Courts.
15 The NOI is only applied to adjudicated offences for adjudicated defendants - i.e.those proven guilty [Guilty verdict/Guilty plea] or acquitted - and is determined according to the following rules:
CONSIDERATIONS WHEN USING THE NATIONAL OFFENCE INDEX (NOI)
16 The assumptions and rules underpinning the NOI, in particular, defining 'offence seriousness' and the subsequent impact of this definition on the ranking of offences, need to be kept in mind when using the principal offence data in this publication. However, it is important to note that these technical issues are only of practical significance where a choice must be made between output categories, which for this publication are the ASOC divisions (see Appendix 4 in the publication). For example, although some sexual and related offences are ranked ahead of drug and related offences, they are unlikely to co-occur.
17 For defendants adjudicated in the Higher Criminal Courts and Magistrates' Criminal Courts in Australia, the majority of these defendants have one offence adjudicated, or offences within the one ASOC division (69%). Therefore, these defendants do not require the application of the NOI.
18 The application of the NOI is currently being investigated further for the ABS Prisoners in Australia collection and collections currently under development. Therefore, the Index may change over time.
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