1 Introduction: Offender volumes

1.1 Report continuity

This is the second edition of the Offender Volumes Report. The report presents information about the offender population managed by Corrections in prisons and in the community. In the following chapters, data is presented separately for offenders in each of the following sub-groups:

  • prison sentenced
  • remanded in custody
  • prison release-ordered
  • community sentenced

This series of reports (in part) replaces the prison census series, published biennially between 1987 and 2003. This year's report is the second in this series which is intended to become an annual online publication.

1.2 Snapshot and throughput perspectives

A number of perspectives on the data are taken in this report. The primary one is a longitudinal view in which a recent "snapshot" of the various offender sub-populations (at 30 June) is presented. In addition comparable monthly "snapshot" data stretching back over more than two and a half decades provides some context. Secondly, a perspective is given on the annual through-put of offenders (as they transition on to new sentence and order episodes managed by Corrections), also in the context of historical trends. All of this data is analysed in terms of offenders' age, gender, ethnicity, offence types, sentence length, and other variables of interest.

1.3 "Major directive" methodology and counting rules, large historic data collection

To support the approach taken in the report, an enriched data set has been established that features some innovative concepts and methods. This is based on the most significant or prevailing directive issued by the Courts or the New Zealand Parole Board to Corrections, in relation to an individual offender. For example, if a recorded directive requires that an offender is sentenced to prison and no order applies indicating that he/she is to be released on or before a particular day, then the offender is counted as "prison sentenced" on that day[1].

A beneficial aspect of producing the data-set from the directives is that it has allowed the incorporation of sentence histories of all offenders managed by New Zealand's Prison and Probation Services since 1980 (and not just information regarding particular census days). This includes the complete, Corrections administered, sentencing histories of all known offenders. Note that this does not include fines or conviction with discharge. Although the original source data is substantially the same as that for other published reports, the counting rules used here differ from those traditionally used for "prison muster" and "community sentence new starts". Instead of providing counts of new sentence starts this report provides counts of transitions between different states of correctional management (see chapter 11 Data source and enrichment methodology for details).

The data quality of the report largely reflects the quality of data in Corrections' "Integrated Offender Management System" (IOMS) database. Like all large historic data collections this data is not without error. However, the methodology used is robust and data checking reveals overall consistency.

1.4 Target audience is on-line technical analysts and policy commentators

The offender volumes report is intended for technical analysts as an introduction to the Corrections' offender volumes data set. It provides a selection of useful graphs with a minimum of commentary enabling technical readers to quickly come up to speed with the scope and accuracy of the data set. The primary publication format is as an electronic document.

1.5 Glossary of terms

There are many places in this report where hyperlinks below the graphs are provided to take the reader to definitions and the glossary of terms. While this works for on-line readers those reading a hard copy are recommended to peruse section 10, Data definitions and groupings.

1.6 Graphical reporting supported by hyperlinked data spreadsheets

The data is presented graphically, thus clearly indicating the trends in volumes of offenders managed over time. However, totals for any given date are also tabulated and these can be located by following a link ("data spreadsheet") at the foot of each graph.

In the sequence of graphs presented, offenders are disaggregated according to gender, age, ethnicity, sentence type, offence type and various combinations of these variables. Where relevant, other forms of disaggregation are also applied.

1.7 "Inventory" approach

In order to simplify the realities of Corrections' operations and relate them to the complex histories of offenders, this report uses an "inventory" approach that requires each offender to be counted only in a single management category on any one day. This provides for detailed analysis on annual "flows and balances" of offenders as they transition into, out of, and between categories of correctional management. This novel perspective highlights, among other things, the extraordinary complexity of Corrections' business, arising from having to manage a great number of individuals as they progress through stages and cycles of criminal justice sanction and management.

In Chapter 9, the Offender Inventory gives this years' offender inventory summary in a form analogous to a financial accounting or inventory management report. In financial accounting both cash flow and balance sheets are provided, while inventory management reports both stock on hand and stock turn-around. In the current report, offender flows and balances in the various management categories are detailed, such that the opening balance, plus inflow less outflow, equals the closing balance. In keeping with this inventory approach, each offender's status at the beginning of the year is expected to be carried forward from the previous year.

1.8 2009 version of Corrections' history

Since the 2007 version of this report, some offenders have had their timelines restated. This years' report is based on a 2009 version of Corrections' history, with a few offenders having their timelines restated compared to the 2007 publication. This means that some comparisons to 2007 data do not align exactly. It is expected that such restatement of history will happen rarely if at all, once the quality of the history is as high as it can be made, and a progressive reporting and accrual process is properly established.

1.9 Offender pool

As the inventory approach provides for ongoing tracking of the management category for each offender, it has been possible to identify periods where offenders are not managed. A useful concept is the "recently managed offender pool". This is the pool of all offenders managed by Corrections at some time within the last ten years, but who are not currently under Corrections management. If an offender has only ever been under remand management without ever being sentenced then they are not counted in this group. This new concept will provide for future enhancements to this report that will shed light on the evolving nature of the offender population of New Zealand.


[1] The term "sentenced muster" is not used in this report as this term has a specific and different meaning in other contexts (generally referring to counts of sentenced prisoners physically present on a prison site on a day). However, prison sentenced offenders may not actually be on site due to hospitalisation, movement to a psychiatric facility, temporary release, escape, death, missing data etc.