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Volume 482: debated on Tuesday 11 November 2008

To ask the Secretary of State for Justice which factors his Department (a) deems relevant and (b) incorporates when making projections for the future prison population in England and Wales. (234883)

There are many factors and data which are incorporated into the prison population projections to greater or lesser degrees. The most significant factors which the Department deems relevant to and incorporates into the projections are:

Trends in sentencing behaviour, such as sentence lengths and custody rates.

Trends in crime, incorporated through the Criminal Justice System model.

Legislative impacts, such as the Criminal Justice and Immigration Act 2008.

Procedural impacts, such as the Simple, Speedy, Summary Justice (CJSSS) scheme, and measures to increase offences brought to justice contributing to PSA24.

Factors which are deemed relevant but cannot be incorporated are those for which there is no agreed timetable, or those for which the effects cannot be projected with reasonable confidence, such as the effects of increased numbers of European arrest warrants resulting from the UK's involvement in the Schengen Information System 2.

More details on the prison projections may be found in the latest published bulletin, “Prison Population Projections 2008-15” Ministry of Justice Statistics Bulletin, 18 September 2008.

To ask the Secretary of State for Justice what forecasting model his Department uses to prepare the annual prison population projections for England and Wales. (234888)

The models used to calculate the current prison population projections are described in Appendix C of the Ministry of Justice publication, “Prison Population Projections 2008-2015”, published on the Ministry of Justice website in September 2008. There are four elements to the modelling. In the short term (and the first two years) most segments of the population are modelled by a combination of stock-and-flow modelling and the use of the X12-ARIMA method developed by the USA Census Bureau. The X12-ARIMA method is available at:

In the longer term (between two and seven years) most segments of the population use the Grove-Macleod model. This has been published in OR Insight Vol. 11 Issue 1, January-March 1998, pp. 3-9, “Forecasting the prison population”. More detail is also available in Occasional Paper 80, “Modelling crime and offending: recent developments in England and Wales” published on the Home Office website in 2003. The population on indeterminate sentences are not projected by these methods, and these segments instead use a system dynamics model developed by the Dangerous and Severe Personality Disorder Programme. In addition to these models, the impacts of some changes in legislation and operational procedures are estimated using the Criminal Justice System Model and, if necessary, one-off bespoke calculations.

To ask the Secretary of State for Justice what account his Department takes of (a) sentencing behaviour and (b) crime rates when making projections for the future prison population in England and Wales. (234889)

The Ministry of Justice publication “Prison Population Projections 2008-15” provides data for three different scenarios (high, medium and low), each of which is generated by a different trend in sentencing behaviour. These are described in section 3 of the publication, and in more detail in Appendix C.

Trends in crime rates are incorporated through the Criminal Justice System Model, which in turn uses data generated from the Home Office’s Crime Trajectory Model. This is described in appendix C of the publication.