1.3 New methodology and counting rules, large historic data collection

To support the approach taken by the report, a new and enriched data set has been established, featuring some new concepts and methods. This is based on the most significant or prevailing directive issued to Corrections, by the Courts or the New Zealand Parole Board, 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 unique aspect of the data-set is the incorporation of sentence histories of all offenders managed by New Zealand’s Prison and Probation Services since 1980. This includes the complete conviction and sentencing histories of all known offenders, excluding convictions not resulting in sentences administered by Corrections (such as fines and discharges). 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 new sentence starts this report quantifies numbers of offenders directed to episodes of correctional management categories, and transitions between such episodes (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 quality to be very good.

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.