Victorian government may have overestimated the 2023 prison population in their planning

Victoria’s prison population has increased by 80% in the last decade, primarily as a result of a “tough on crime” approach by both sides of politics

The annual cost of running the state’s prisons is now more than $1.6 billion, triple the outlay in 2009-2010. As well, the government announced a record $1.8 billion in new capital spending on prison infrastructure over four years in a bid to accommodate 1600 more prisoners.

Projections released exclusively to The Age reveal that the growth will continue into the foreseeable future: the Andrews government expects prisoner numbers to soar from 8110 today to 11,130 by June 2023.

This is a simple system dynamics model of the prison population

From published figures is possible to model the rates of prison release, recidivism and first offender incarcerations up until 2019 and then project for the next four years until 2023.

The model has a number of assumptions: that the recidivism rate will be 43% after two years, that the average stay in jail is slightly over one year and that incarceration rates will be linear based on 2008 – 2019 figures. Release and recidivism rates rise in line with the increase of incarceration.

The difficulty with this linear projection is that it shows no sign of flattening. It is reasonable to assume that sometime in the future incarceration rates will plateau. When is a question.

Given these assumptions and these increasing rates of incarceration, The model shows the growth in the gaol population.

The projection for the prison population in 2023 is 9600, 15% below the government’s estimate of 11,130.

For the prison population to reach the government’s estimated total, there would need to be an increase in incarceration rates, recidivism rates or sentence length.

At present, there is nothing to suggest that these rates will change.

However, the government plans to increase the number of beds in prisons by 1600 over the next four years. This will take prison capacity in Victoria to 9700, just 100 above the total projected in the model.