The main determinants of the size and composition of the prison population in England & Wales

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This Report has been compiled using a variety of data analysis and simulation methods, assessing published statistics on the operation of the criminal justice system in England and Wales. The main aim has been to help clarify the main determinants of the size and composition of the prison population, and to assist the development of evidence based policies and practice, exposing those factors which have contributed to the rise of the prison population and the persistence of current levels. The results of this quantitative work are summarised in the form of answers to four questions.  The Report has been commissioned by the Hadley Trust in conjunction with Crest Advisory

The application of scientific, quantitative methods to questions of policy and practice in criminal justice
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A. Since 2006, what have been the most important determinants of the increasing prison population?

2.  The introduction of the Criminal Justice Act 2003 and subsequent changes to sentencing practice have had major impacts, sometimes working in opposite directions:

      a. Longer sentences for most offence types have added to the prison population

      b. Indeterminate public protection (IPP) sentences have added to the prison population

      c. Suspended sentences have acted to reduce pressure on prisons but will have drawn also from community sentences

      d. Longer sentences and the introduction of post-licence supervision for short sentence prisoners in 2014 have added to the pool from which recalls to prison are drawn
3.  The impact of austerity measures on police and other criminal justice agencies has focussed effort on more serious offences and prolific offenders. This has meant that:

      a. the annual flow to sanction outcomes such as cautions, fines, and, to a lesser degree, community sentences have declined substantially

      b. custody and suspended sentences have stayed broadly the same with minor falls in immediate custody taken up as suspended sentences

      c. initial increases in the number sentenced for theft and robbery offences fell significantly from around 2010 (likely to be linked to abandonment of the serious crime target)

B. Which offence groups currently represent the biggest volumes within the prison population?

4.  The largest groups in prison by offence category are violent and sexual offenders

5.  Those on long sentences represent by far the largest groups; ~15%, indeterminate sentences; ~ 43 %, for 4+ years

6.  Recalled offenders in 2016 comprised ~9% of the population

7.  Repeat offenders make up the largest groups in custody, or under supervision on suspended and community sentences. Over the period 2006 - 2016, prison has progressively come to hold the highest concentration of repeat offenders with multiple offences

8.  The prison population has become progressive older

C. What impact have mandatory minimums and IPPs had on the overall prison population, relative to other policy changes?

9.  We estimate that the introduction IPP sentences, on its own, will have added to the prison population around 4,000 places

10.  We estimate that the impact of sentence length inflation has resulted, by 2017, in around 12,500 more male prisoners

11.  Combining these two changes (they are not additive due to various feedbacks in the justice the system, such as further offending) represents 15,000 more male prisoners by 2017

12.  The number of female prisoners is not significantly impacted by these changes

13.  Without the suspended sentence provisions of the Criminal Justice Act 2003, the prison population would have been ~10,000 higher for males and 3,000 for females, than current levels. This scenario assumes that both IPP and sentence length inflation remain in place.

D. It would appear that more punitive sentence lengths have offset falls in the numbers before the courts, use of remand and time served. Can we test this?

14.  The volumes of sentencing flows show that, whatever 'premium' might have been expected from a general reduction in the number of offenders entering the system, this has not significantly impacted on the rate of entry of first time offenders to prison.

15.  The number of offences that are sufficiently serious to call for prison, notwithstanding any general presumption that the lightest sentence possible should be used for first time offenders, has remained broadly constant over the last 10 years.

16.  The concentration of offenders with long criminal histories in prison is in keeping with the notion that prison is reserved for the most serious or prolific offenders, leaving little scope for any more general reduction of the number before the courts to have an impact.