Prison Population Projections 2014 – 2020 
3. Modelling methodology and projection scenarios  
The prison projections model is part of wider work within the Ministry of Justice 
to develop a consistent and coherent suite of models of the criminal courts 
and offender management, driven by common projections of demand for the 
Ministry of Justice’s services.  
The custodial convictions model uses projections of numbers of defendants 
entering the criminal courts. In order to project volumes of defendants being 
given a custodial sentence, it also takes 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 population projections model takes projections of custodial 
convictions, converts them to projections of prison receptions and then models 
the amount of time that offenders spend in prison to calculate the resulting 
prison population.  
The benefits of this method are that it allows us to: 
 explicitly project custodial convictions (rather than just convictions); 
 understand the Criminal Justice System factors which contribute to 
change in the prison population, such as time served, sentences given, 
trial and sentencing court changes or shifts in defendant 
demographics; and 
 more easily model the impact on the prison population of specific 
Ministry of Justice and other Criminal Justice Agency policy changes 
relating to specific offences or specific sentences.  
Appendix B provides details of the methods used to produce the prison 
population projections and the assumptions behind them. 
The assumptions informing these projections, and therefore the projections 
themselves, are subject to significant uncertainty. This is represented by the 
three scenarios, with each scenario being only as likely as the assumptions 
which inform it. 
The method used for generating projections of the prison population in 
England and Wales for the 2014-2020 projections is consistent with the 
approach used to generate the 2013-2019 projections published on 7 
November 2013. 
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