Prison Population Projections 2014 – 2020 
 
At the core of the method is a model of flows of offenders into and out of 
prison which counts the resulting prison population each month for sentenced, 
recall and remand prisoners.  
Inputs to the prison projections model include projections of future custodial 
convictions. These are generated from time series projections of numbers of 
defendants entering the criminal courts and take into account the age, gender 
and offence of defendants entering the system, the flow of cases through the 
courts and the sentences which concluded cases attract. 
The prison projections model monitors the sizes of the sentenced, recall and 
remand prison populations. These populations depend on the inflows defined 
above and the outflows.  These outflows are defined by observed distributions 
of custodial sentence lengths, and the proportion of custodial sentences 
served for subsets of these populations. The model also simulates the ageing 
of the prison population over time. 
The projection model is based on data up to June 2014 from various sources 
including court proceedings and performance data, sentencing data and 
prison receptions and population data. 
The results of the prison projections model are supplemented with an estimate 
of the future non-criminal and fine defaulter populations, which is based on the 
latest available data to September 2014. 
Three scenarios have been modelled. These scenarios track the impact of 
three different incremental changes in sentencing behaviour: 
 The Central Scenario assumes custodial convictions are broadly in line 
with recent trends.  The average length of sentence is assumed to be 
flat based on recent trends in sentence lengths. This broadly reflects 
the assumptions for Scenario 2 in the November 2013 projections. 
We also consider two illustrative scenarios 
 Scenario 1 assumes that custodial convictions will fall against recent 
trends.  The average length of sentence is assumed to be lower than 
what has been observed in recent trends in sentence lengths.  
 Scenario 2 assumes a rise in custodial convictions when compared to 
recent trends.  Also the average length of sentence is assumed to be 
higher than what has been observed in recent trends in sentence 
lengths. 
The three scenarios also incorporate the impact of: 
 trends in the age, gender and offence of defendants entering the 
system and in the flow of cases through the courts; 
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