Prison Population Projections 2014 – 2020 
1) Producing projections of defendants proceeded against 
Projections of defendants proceeded against at court are chosen as the entry 
point to the modelling system because this is the entry point of defendants into 
the MoJ’s area of responsibility.  Underlying crime levels and the activities of 
the police and CPS will have an impact on the volume of defendants 
proceeded against.  
The Demand Projections Model produces baseline projections of all 
defendants proceeded against at court for 12 high-level offence categories. 
This is based on historical time series data (January 2002 to June 2014) at a 
monthly resolution out to 2020, sub-divided by region and age for the 
Magistrates’ court and region for the Crown Court.  
The demand projections are based on time series forecasting methods such 
as Seasonal Exponential Smoothing (SES). A ‘middle-out’ forecast is used, 
centred at the offence level. The other levels in the hierarchy are reconciled so 
that the levels below (e.g. region or offender age) when disaggregated, and 
the levels above (i.e. totals) when aggregated, are consistent with the 
forecasts derived at the offence level.     
It should be noted that these projections cannot be expected to track actual 
volumes of defendants proceeded against if there is any sudden or cumulative 
change which takes demand volumes or offence mix well outside the trends 
seen historically. 
 
2) Converting the demand projections into custodial convictions 
A Courts and Sentencing Module converts the demand projections into a set 
of projections of disposals by disposal type (including custodial convictions), 
offence, sex and age band at a monthly resolution. These projections of 
custodial convictions by sex, age and offence type are used as a key input for 
the Prison Population Stock-Flow model. 
The Courts and Sentencing Module is a combination of the Magistrates’ and 
Crown Court Workload Models and the Sentencing Module. The demand 
projections are used as an input into a Magistrates’ Workload Model, which 
uses historical data to split defendants into court routes (Table B1) and tracks 
their flow through the system. 
The Crown Court workload model takes forecasts of caseload and assigns 
various attributes (e.g. early guilty plea, effective trial mix) to estimate likely 
hearing times and the resulting flow of cases through the system. The cases 
disposed of are then converted to the number of defendants disposed of using 
recent data for the observed ratio between cases and defendants.  
The key assumptions that are used in the Courts and Sentencing Module are: 
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