Scottish prison population projections

7 Conclusion

Prior to the pandemic, the Scottish Government used time-series based forecasting methods applied to prison population trends to provide 12-month prison projections. This method extrapolated projected future prison populations from past trends, so it could not model changes to the prison population that were not already reflected in historical trends, such as the impact of the pandemic. The microsimulation approach overcomes some of these issues by allowing assumptions to be made about court throughput, a key determinant of changes to the prison population in the short term.

For several reasons, modelling the future using the microsimulation gets less accurate the further ahead it is projected (whether due to systematic errors in the model, inaccurate assumptions due to unforeseen circumstances, or due to changed circumstances that the model is not built to account for). Experience to date suggests that to ensure reliable projections, forecasting six months into the future is the limit.

As previously highlighted, the main determining factor for changes in the prison population in the short term will be the court recovery programme changes, which may contribute to reducing the backlog of scheduled solemn trials. However, if the number of complaints and/or indictments to court for accused individuals were to increase compared to recent historical levels this could balance against increased case throughput and result in the number of scheduled trials remaining high.

The Crown Office and Prosecution Service (COPFS) have reported^[25] that there is uncertainty whether their overall volume of casework will continue to grow but violence against women and children, sexual crime and domestic abuse will likely persistently account for a large proportion of its casework for some years to come. Furthermore, COPFS indicate that the continued increase in complex cases requires longer investigations and court hearings.

In the longer term, changing prison population inflows will be impacted by changes in the crimes recorded and prosecuted.