Author Nick Halloran, Ewan Watson and Don Weatherburn
Published February 2017
Report Type Crime and Justice Bulletin No. 203
Subject Bail / Remand; Parole; Prisons and prisoners; Statistical methods and modelling
Keywords Simulation model, prison, parole, bail, policy, criminal justice system

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To describe a simulation model of the NSW prison system and demonstrate its utility as a tool for examining the effects of changes to the criminal justice system that influence the number of prisoners in custody.


The model consists of four states (bail, remand, custody and parole) and a set of parameters governing flows into and out of those states as well as lengths of stay in each state. Data for the model were sourced from police, court and correctional databases.


The prison system is extremely sensitive to changes in the percentage of persons refused bail. A one percentage point change in the percentage of persons refused bail by a court increases the remand population by 7.66 per cent, the sentenced prisoner population by 6.03 per cent and the parole population by 6.15 per cent.


It is feasible to build a simple model of the prison system which is easy to maintain but nonetheless useful in analysing the likely consequences of changes in arrest, bail and sentencing policy.

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