Crime Harm Index

Crime Harm Index (Beta Version 5) Provisional User Guide

Research and Evaluation, Strategy Group, New Zealand Police January 2017

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NZ Police Crime Harm Index – Beta Version 5 – PROVISIONAL User Guide

Contents 1.

Introduction ............................................................................................................................... 3

1.1

What is the CHI?......................................................................................................................... 3

1.2

Why was the CHI developed? .................................................................................................... 3

1.3

What’s in this guide?................................................................................................................... 4

2.

CHI methodology ...................................................................................................................... 4

2.1

Guiding principles ....................................................................................................................... 4

2.2

CHI development process .......................................................................................................... 4

2.2.1 Process summary ........................................................................................................................ 4 2.2.2 Calculation of Equivalent Prison Days ........................................................................................ 5 2.2.3 Imputation for rare offence codes ............................................................................................. 6 2.2.4 Testing and validation ................................................................................................................ 6 2.2.5 Caveats and limitations of the CHI ............................................................................................. 6 3.

How to use the CHI ................................................................................................................... 7

3.1

Using the CHI ............................................................................................................................. 7

3.1.1 Code consideration and selection .............................................................................................. 7 3.1.2 Applying CHI weightings ............................................................................................................. 7 3.1.3 Aggregating to offence groupings .............................................................................................. 8 3.1.4 Referencing the CHI .................................................................................................................... 8 3.2

Example applications for the CHI ............................................................................................... 8

4.

References .............................................................................................................................. 12

Prepared by: Sophie Curtis-Ham, Research and Evaluation Unit, Strategy Group

Reviewed and authorised by: Darren Walton, Director Research and Evaluation, Strategy Group Provisional Guide for CHI Beta Version 5 Released January 2017 IN CONFIDENCE


1. Introduction This document provides users of the proposed New Zealand Crime Harm Index (CHI) with a guide to its use and background information about how the CHI was developed. Currently, the NZ CHI is in Beta Version while awaiting external peer review which may result in changes to the methodology. This guide is therefore provisional and available to initial users trialling the Beta Version with the caveat that the final version may produce different results (though unlikely to differ significantly).

1.1 What is the CHI? The Crime Harm Index is a score that seeks to differentiate crime types based on a measure of the harm caused by each crime type. In the absence of a true measure of harm it relies on the use of sentencing data as a proxy for the harm caused. The CHI is derived from the application of a metric which weights each crime based on the harm it causes, relative to other crimes. The CHI therefore allows weighted crimes to be aggregated to provide an overall measure of harm to society, as opposed to traditional measures of crime volume where all crimes are counted equally. The weightings are an estimate of the starting point sentence for a first offender, excluding the particular aggravating or mitigating circumstances of the specific instance of the crime and the offender. The estimated starting point sentence is used because it is considered to be the best reasonably available ‘proxy’ for the relative harm caused by a given offence. The weightings are derived from actual charge and sentencing outcomes following the methodology set out in section 2. The CHI metric is provided with this guide in the form of a spreadsheet which contains the weightings for each Offence Code. The most recent version is Beta Version 5.

1.2 Why was the CHI developed? The recent rise in harm-focused policing and calls for the development of practical metrics which enable crime harm to be quantified (Ratcliffe, 2015a, 2015b; Sherman, Neyroud & Neyroud, 2016), offer an opportunity to improve on volume based analysis approaches to measuring crime. In response, CHIs have been developed in several overseas jurisdictions and have been applied in various ways, such as1: 

Performance measurement and analysis: tracking total harm from crime over time and identifying changes and inter-district differences in the ‘harm profile’ (e.g. what proportion of harm is made up by different offence types).



Resource targeting: Harm-spotting to identify hotspots weighted by harm or identifying the victims or offenders who account for the most harm, to assist in targeting crime prevention activities to the highest concentrations of harm.



Evaluation: testing effectiveness of policing and crime reduction interventions by comparing not just volumes but harm indices before and after (e.g. has the harm reduced and by how much, are offenders reoffending less harmfully).



Triaging: Factoring harm into offender risk assessment and triaging decisions (e.g. out of court proceedings and interventions).

The NZ CHI has been developed to facilitate all of the above and for wider use by other justice sector agencies. Further details about potential applications for the CHI are provided in section 3.

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See for example, Ratcliffe, 2015a, 2015b; Sherman, Neyroud & Neyroud, 2016; Bland & Ariel, 2016.

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1.3 What’s in this guide? This guide sets out the methodology used to develop the NZ CHI (section 2), and guidance for users wanting to apply the CHI in their work (section 3.1). Practical examples of CHI applications are also described (section 3.2). If you have an example you would like to contribute to future versions of this guide so that innovative use can be shared amongst all CHI users, please send the details to: [email protected].

2. CHI methodology 2.1 Guiding principles The overarching principle guiding the development of the NZ CHI was to replicate closely the UK’s Cambridge CHI (Sherman, Neyroud & Neyroud, 2016). An exact replication was not possible as the Cambridge CHI is based on the starting point sentence for a first offender set out in official sentencing guidelines. NZ does not have such guidelines so the NZ CHI was based on actual sentences delivered by the Courts converted as best as possible to an equivalent to the starting point for a first offender for any given offence.2 We also followed the Cambridge CHI approach in translating non-custodial sentences into an equivalent number of days in prison, and translating custodial sentences into the time served in prison before release (e.g. on parole). However, where the Cambridge CHI translates custodial sentences into the minimum time to serve in prison before being eligible for potential release (e.g. on parole), we used the average time actually served, for several reasons. First, to maintain proportionality between short (2 years or less) and long (more than 2 years) sentences. These are treated differently in NZ legislation, resulting in the anomaly that an offender could serve the same minimum time for a 3 year sentence (if paroled on earliest possible date at 1/3 of the sentence) as a 2 year sentence (released at ½ of the sentence)3. Second, to reflect the fact that offenders sentenced to long sentences typically serve much longer than a third of their sentence4. Third, to ensure that the translation of Home Detention sentences into equivalent prison days was commensurate with the equivalence found in sentencing practice, which equates one year of Home Detention with two years imprisonment (which is one year of time served in prison)5.

2.2 CHI development process 2.2.1 Process summary The CHI is derived from a sentencing dataset provided by the Ministry of Justice (MOJ) containing the outcomes of charges for the period 2004-2015 inclusive. Relevant outcomes and sentences were translated into “Equivalent Prison Days” (EPD). For each offence code where there were at least 5 eligible charges6 between 2011 and 2015 (or 2004-2015 for codes where there were 2 years

= sentence length in days * .74

The number of days before release, based on average portion of sentence served9.

Life imprisonment

= 5,337

The number of days before release, based on average length of sentence served10.

Preventive Detention

= 5,182

The number of days before release, based on average length of sentence served11.

EPD Formula

Rationale

= fee $ / (15.25 * 8)

Regardless of actual sentence, the minimum penalty for these offences are the set fees, so for these codes the fee was used instead of a 15th percentile. Formula is the same as for fines to convert $ into EPD.

Offence code Where A-Z code had a set infringement fee12

Other sentences and orders which are more reflective of offender circumstances and needs than the harm of the offence were excluded from the analysis as containing more ‘noise’ than ‘signal’. These included Intensive Supervision, Supervision, rehabilitative programmes, driving/licence restrictions and secure treatment. Charges

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Sentencing Act 2002. Statistics provided by the Department of Corrections, personal communication, September 2016. Derived from all first releases from long sentences for the financial years 2012/13, 2013/14, 2014/15 and 2015/16. 10 Statistics provided by the Department of Corrections, personal communication, September 2016. Derived from all first releases from life sentences for the financial years 2012/13, 2013/14, 2014/15 and 2015/16. 11 Statistics provided by the Department of Corrections, personal communication, September 2016. Derived from all first releases from preventive detention sentences for the financial years 2012/13, 2013/14, 2014/15 and 2015/16. 12 Source: table provided by NZ Police Data Quality Team. Some codes were missing (as identified in the testing of CHI vB1) so the table was updated manually with the fees for these codes and incorporated into future versions. 9

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relating to corporations rather than individuals were also excluded as likely to overinflate CHI values for offences which resulted in large fines of corporate entities.

2.2.3 Imputation for rare offence codes For some codes, there were fewer than 5 charges with calculable EPDs to generate a 15th percentile, requiring imputation from similar offences. For the 1000-9000 series13, codes with n=5). If n