How the measure of proven reoffending has changed and the effect of these changes
Source: data.gov.uk (2018-05-25)

Proven Re-offending statistics. Key statistics on proven reoffending in England and Wales. It gives proven reoffending figures for offenders who were released from custody, received a non-custodial conviction at court, or received a caution or reprimand.

1 
 
 
 
 
 
 
 
 
How the measure of proven reoffending 
has changed and the effect of these 
changes 
 
 
 
 
 
 
 
 
26th October 2017 
 

 
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How the measure of proven reoffending has changed  
 
Background 
 
In “Transforming Rehabilitation: A Strategy for Reform”, published in 2013, plans were set out to introduce 
a new system for the management and rehabilitation of offenders in the community across England and 
Wales. 
In February 2015, various reforms were implemented. These included:   
• 
opening up the market to a diverse range of rehabilitation providers from the private, voluntary 
and social sectors through 21 Community Rehabilitation Companies (CRCs);  
• 
using a ‘payment by results’ approach to develop and implement effective ways of rehabilitating 
offenders and rewarding providers that devise and deliver the most effective rehabilitation 
programmes; 
• 
extending statutory rehabilitation to short-sentenced offenders released from prison, who have 
the highest reoffending rates and yet previously received no supervision after release;  
• 
reorganising the prisons to resettle offenders ‘through the gate’, with continuous support from 
custody to community; and 
• 
creating a new public sector National Probation Service (NPS) to manage high risk offenders. 
 
Following implementation of these reforms, a public consultation was run in summer 2015, proposing 
several changes to the Proven Reoffending National Statistics in order to support the reforms to the system 
and ensure the Ministry of Justice continued to meet its commitment of statistical best practice by giving a 
coherent overview of all statistics relating to reoffending.  
 
Users’ views were invited to the proposed changes, and 19 responses were received to the consultation. A 
response to the consultation was published in April 2016 and set out the changes: 
www.gov.uk/government/uploads/system/uploads/attachment_data/file/519644/proven-reoffending-
consultation-response.pdf 
 
The main changes to the methodology are: 
 
- Moving to a three month cohort. The latest publication reports on offenders who are released from 
custody, received a non-custodial conviction at court, or received a caution within a three month period, 
for all measures of reoffending, including for juveniles. Previously, a 12 month cohort was used. 
 
- Production of adjusted reoffending rates for adults (alongside the raw rates). The Offender Group 
Reconviction Score (OGRS) has been used to adjust the raw reoffending rates for adults, to take 
account of the influence that differences in offender mix can have on the binary reoffending rates.  
 
- A change from calendar year to financial year, for annual figures. Previously, the annual publication 
was in October each year, and based on a calendar year. The annual reoffending publication will now be 
published in January each year and will be based on a financial year. Annual figures will be formed by 
taking a weighted average of the four preceding 3 month offender cohorts. 2015 annual figures will be 
published on the 25th January 2018. 
 

 
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In addition, there is a change in the data source for compiling MoJ’s proven reoffending statistics to better 
reflect the way in which offenders are now managed by the probation services. The data source is called 
national Delius (nDelius) and is the established case management system for use by probation services. 
nDelius has already been used to compile the published interim Payment by Result (PbR) figures for CRCs 
and the NPS since October 2016. 
 
The first set of proven reoffending statistics being published using the new methodology and data source 
are for the October to December 2015 cohort. They are being published alongside the first set of final 
results for the Community Rehabilitation Companies (CRCs) and the National Probation Service (NPS). 
These are the results by which CRCs’ performance will be assessed for PbR.  
 
The new approach creates one consistent measure of proven reoffending and allows users to relate 
the performance of the CRCs in reducing reoffending with the overall figure for England and Wales. 
 

 
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The impact of the changes 
For adult and juvenile offenders, the new measure is based on all offenders released from custody, 
receiving a non-custodial conviction at court or receiving a caution within a 3 month period (Figure 1). The 
previous measure reported on adults and juvenile offenders within a 12 month period. Changing from 12 
month offender cohorts to 3 month offender cohorts results in a greater proportion of prolific offenders and 
hence higher reoffending rates. 
Figure 1  
 
 
Table 1 shows the proportion of offenders with a proven re-offence using the new measure of reoffending 
and the previous measure of reoffending. The first columns compare the latest annual figures (for April 
2014 to March 2015) using the previous measure based on a 12 month cohort and the new measure based 
on a weighted average of the four preceding 3 month cohorts. It can be seen that reoffending rates are 
around 4-5 percentage points higher using the new method, for both adult and juvenile offenders than the 
previous method. 

 
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Table 1: Proportion of adult and juvenile offenders who reoffend in the current measure and new 
measure 
  
New 
annual 
average 
Previous 
12 month 
cohort 
New 3 month cohort 
  
Apr 
2014-
Mar 
2015 
Apr 2014-
Mar 2015 
Jan-Mar 
2015 
Apr-Jun 
2015 
Jul-Sep 
2015 
Oct-Dec 
20151 
Adult offenders 
  
  
  
  
  
  
Proportion of offenders who reoffend (%) 
28.9 
24.3 
28.2 
28.5 
28.2 
28.7 
Adjusted2011 proportion of offenders who reoffend (%) 
28.6 
- 
28.1 
28.3 
28.3 
28.4 
Average OGRS4/G score 
33.7 
- 
33.5 
33.6 
33.3 
33.7 
Average number of reoffences per reoffender 
3.68 
3.22 
3.70 
3.70 
3.74 
3.82 
Number of reoffences 
544,719 
344,914 
132,607 
130,195 
128,839 
132,262 
Number of reoffenders 
148,130 
107,031 
35,835 
35,143 
34,456 
34,594 
Number of offenders in cohort 
512,684 
441,133 
127,046 
123,432 
122,344 
120,687 
Average number of previous offences per offender 
17.64 
14.23 
17.60 
18.07 
17.93 
18.31 
  
  
  
  
  
  
  
Juvenile offenders 
  
  
  
  
  
  
Proportion of offenders who reoffend (%) 
42.6 
37.9 
43.3 
42.9 
41.9 
41.8 
Average number of reoffences per reoffender 
3.61 
3.30 
3.64 
3.70 
3.71 
3.88 
Number of reoffences 
69,319  
45,278  
16,648  
 15,840  
  15,555  
15,256  
Number of reoffenders 
19,186  
13,740  
4,568  
4,276  
4,194  
 3,930  
Number of offenders in cohort 
45,042  
36,260  
10,538  
9,978 
9,999  
 9,405  
Average number of previous offences per offender 
3.56 
2.51 
3.63 
3.55 
3.50 
3.59 
  
  
  
  
  
  
  
All offenders 
  
  
  
  
  
  
Proportion of offenders who reoffend (%) 
30.0 
25.3 
29.4 
29.5 
29.2 
29.6 
Average number of reoffences per reoffender 
3.67 
3.23 
3.69 
3.70 
3.74 
3.83 
Number of reoffences 
614,038 
390,192 
149,255 
146,035 
144,394 
147,518 
Number of reoffenders 
167,316 
120,771 
40,403 
39,419 
38,650 
38,524 
Number of offenders in cohort 
557,726 
477,393 
137,584 
133,410 
132,343 
130,092 
Average number of previous offences per offender 
16.50 
13.34 
16.53 
xx-xxxx-xxxx 
17.24 
 
In addition to the change in cohort, in October 2015 there is also a change in the data source used to 
compile the statistics (see Annex A). Proven reoffending statistics have, until now, been based upon 
information drawn from the Inmate Information System to identify those offenders discharged from custody. 
For the latest proven reoffending statistics, custodial discharges have been taken from the national Delius 
system for adults and from the Prison-Nomis system for juveniles. The reason for changing to nDelius is to 
ensure the proven reoffending statistics align with reoffending statistics produced for the Community 
Rehabilitation Companies, and because nDelius has become the main system for managing the flow of 
adult offenders. As juveniles are not managed by the probation system in the same way as adults, 
                                                          
1 Users should not compare the October to December 2015 cohort with previous cohorts, due to a change in data 
source and potential variability.  

 
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offenders discharged from Youth Offender Institutions are now taken from the Prison-Nomis system. The 
change for juveniles also reflects the availability of a more accurate data source.     
This change in October 2015 introduces potential variability and therefore users should be cautious when 
making any comparison with the October to December 2015 cohort and earlier cohorts. It is estimated the 
impact of changing data source is an increase in the reoffending rate of around 0.5 percentage points. The 
driver for this increase appears to be among offenders discharged from custody after serving less than 12 
month sentences, and might be connected to the introduction of statutory supervision for this group. Further 
investigation is ongoing. The impact of changing data source for juveniles discharged from Youth Offenders 
Institutions is marginal.   
 
Trends over time 
 
Despite the increase in the reoffending rate, both measures show similar trends over time.  
 
The adult proven reoffending rate has remained fairly flat over time (Figure 2), fluctuating between 28% and 
31%. Among juveniles there has been an increase in the proven reoffending rate since 2005 of around 4 
percentage points, using both methodologies. However, the size of the offender cohort has reduced 
considerably for juveniles over the same period. 
 
Figure 2: Proportion of adult and juvenile offenders in England and Wales who commit a proven 
re-offence, October 2005 to December 2015 
   
0
5
10
15
20
25
30
35
40
45
Proportion of offenders who reoffend (%)
Change of data source for
Oct-Dec 2015 cohort
Adult existing measure
Adult new measure
Juvenile existing measure
Juvenile new measure
 
 
 
There is also a similar trend in the proven reoffending rate when comparing by index disposal (Figure 3), 
with the adult proven reoffending rate for custody and court orders now around the lowest level since 2005.  
 

 
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Figure 3: Proportion of adult offenders released from custody or given a court order who 
commit a proven re-offence, October 2005 to December 2015 
 
 
Although the trend is broadly the same by disposal, there is an impact on the October to December 2015 
cohort from changing data source. This is particularly noticeable among offenders discharged from custody, 
and within that the biggest impact is among the less than 12 months custodial sentence length group. This 
might be connected to the introduction of statutory supervision for this group and a data source which 
tracks offenders better; and further investigation is ongoing. 
 
Adult adjusted reoffending rate: 
 
The Offender Group Reconviction Scale (OGRS4/G) is used to control for some differences in offender 
characteristics across different offender groups. OGRS4/G uses age, gender and criminal history to assess 
the reoffending risk of a given group of offenders by producing a score between 0 and 1. A higher score 
means an offender is more likely to reoffend.   
The reoffending rates are adjusted to 2011 in line with Payment by Result statistics. In the example below, 
we would say that the proven reoffending rate for the period April 2014 to March 2015 has reduced since 
2011. However, the average OGRS score has increased, meaning that the cohort of offenders is more 
likely to reoffend. As a result, when we control for changes in offender characteristics the adjusted 
reoffending rate fell by 1.6 percentage points since 2011. 
 
 
 
 

 
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0
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
Adjusted proportion of offenders who reoffend 
(%)
Average OGRS4/G score
Average OGRS4/G score
Adjusted 2011 proven reoffending rate
Raw reoffending rate
Change of data source for
Oct-Dec 2015 cohort
OGRS4/G adjusted reoffending rate for adults example 
England and Wales 
2011 comparison year 
Cohort period (April 
to March 2015) 
Difference 
Average OGRS4/G 
score 
33.4 
33.7 
+0.3 
Proportion of 
offenders who 
reoffend (%) 
30.2 
28.9 
-1.3pp 
OGRS4/G adjusted 
reoffending rate (%) 
30.2 
28.6 
-1.6pp 
 
In the latest publication, the raw reoffending rates have been adjusted using OGRS4 to take account of the 
influence that differences in offender mix have on the binary reoffending rate.  
 
Between 2005 and 2011, the average OGRS score increased, but since 2011 it has remained broadly flat 
(Figure 4). This suggests that between 2005 and 2011 the cohort had an increasing propensity to reoffend, 
but this has since levelled off. As a result, the raw reoffending rate for adults is adjusted upwards between 
2005 and 2011, reflecting the cohort having a greater propensity to reoffend. Since 2011, the raw rates and 
the adjusted rates have tracked each other more closely. For example, the raw reoffending rate for adults 
for the October 2014 to September 2015 period was 28.4%, but the adjusted rate was 28.3%.  
 
Figure 4: The average OGRS scores (2011 adjusted) and the adjusted proven reoffending rate for 
adults, October 2005 to December 2015 
 
 
 
 
 
 
 
 
 
When looking at adult reoffending rates by index disposal, there has been a slight decline in the average 
OGRS scores since 2011 for custody and court orders (Figure 5). This reflects that the cohort is less likely 
to reoffend and therefore the adjusted rate is slightly higher than the raw rate. This is similar to the trend we 
see for Community Rehabilitation Companies. 

 
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Figure 5: The average OGRS scores (2011 adjusted) and the adjusted proven reoffending rate for 
adult offenders released from custody or given a court order, October 2005 to December 2015 
 
To date, it has not been possible to produce an adjusted reoffending rate for juveniles, but work in this area 
is ongoing.  
 

 
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The change in methodology 
The following section provides detail regarding the change in methodology, data sources and the 
geographical breakdowns available. The tables below provide a comparison of the previous methodologies 
with the new approach. 
 
 
Previous measure of proven 
reoffending 
New measure of proven 
reoffending 
The cohort 
All offenders who were released 
from custody, received a non-
custodial conviction at court, or 
received a caution within a twelve 
month period. 
All offenders who were released 
from custody, received a non-
custodial conviction at court, or 
received a caution within a three 
month period. 
The follow-up period to 
measure reoffending 
12 months for offences to occur 
and a further 6 months for 
offences to be proven in court. 
No change. 
What counts as a 
proven reoffence 
Offences committed within the 
follow-up period which were 
proved by a court conviction or 
caution/reprimand or final warning 
either within the one year follow-
up period or in a further six 
months. 
No change. 
Annual reoffending 
rates 
Annual figures based on a 
calendar year and published in 
October. 
Annual figures based on weighted 
average of 4 three month cohorts. 
Based on a financial year and 
published in January. 
Use of a predicted rate 
of reoffending 
None. 
Offender Group Reconviction 
Scale used to adjust raw adult 
rates of reoffending. 
 
Change in data source: October 2015 onwards 
 
Previous measure of 
proven reoffending 
New measure of proven 
reoffending 
Data source for adult 
custodial discharges  
Inmate Information System 
National Delius 
Data source for juvenile 
custodial discharges 
Inmate Information System 
Prison-Nomis 
 

 
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Geographical breakdown 
 
Previous measure of 
proven reoffending 
New measure of proven 
reoffending 
Geographical data tool  
Contains data on the number 
of offenders in the cohort, 
reoffenders and reoffences 
by sex, age and index 
offence (excluding LTLA and 
YOTs) by:  
• 
England and Wales 
• 
Region 
• 
County 
• 
Upper Tier Local 
Authority (UTLA) 
• 
Lower Tier Local 
Authority (LTLA) 
• 
Youth Offending 
Team (YOT) 
This data was published 
based on 12 month cohort 
periods from 2005 onwards.  
No change in breakdowns 
published in this data tool. 
Change in cohort periods 
provided in this data tool. The 
data is published using annual 
figures based on weighted 
average of 4 three month 
cohorts which are based on 
financial years from April 2005 to 
March 2015. From March 2015 
onwards, three month cohorts 
are published until a complete 
financial year is available (the 
next complete financial year will 
be available from January 2018). 
Prison/Youth Secure 
Accommodation/Probation 
Region data tool 
This pivot table contains data 
on the number of offenders 
in cohort, reoffenders and 
reoffences by the following 
categories: 
• 
Type of custody by 
individual 
prison/youth offender 
institution/secure 
training centre/secure 
children's home and 
sentence length. 
• 
Probation region by 
sentence type. 
This data was published 
based on 12 month cohort 
periods from 2007 onwards. 
Prisons included in this data tool 
for all cohorts before October-
December 2015 are based on 
prisons that were operating up to 
the end of September 2015. 
Data are missing for prisoners 
released from prisons in 
previous years that are no longer 
operational. 
Prisons data is only reported up 
until September 2015, due to 
data quality issues in the 
October to December 2015 
cohort. Work is ongoing to 
improve data quality so that this 
can be produced in the future.  
Change in cohort periods 
provided in this data tool. The 
data is published using annual 
figures based on weighted 
average of 4 three month 
cohorts which are based on 

 
12 
 
financial years from April 2005 to 
March 2015. From March 2015 
onwards, three month cohorts 
are published until a complete 
financial year is available (the 
next complete financial year will 
be available from January 2018). 
 
Contact 
Press enquiries should be directed to the Ministry of Justice press office: 
Tel: xx-xxxx-xxxx 
Email: xxx@xxx.xx  
Other enquiries about these statistics should be directed to the Justice Statistics Analytical Services 
division of the Ministry of Justice: 
Nick Mavron, Head of Prison, Probation, Reoffending and PbR Statistics 
Ministry of Justice, 7th Floor, 102 Petty France, London, SW1H 9AJ 
Email: xxx@xxx.xx 
 
 
© Crown copyright 
Produced by the Ministry of Justice 
Alternative formats are available on request from xxx@xxx.xx

 
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 Juvenile custodial 
releases from Secure 
Children Home’s and 
Secure Training Centres. 
eAsset system
Juvenile custodial 
releases from Youth 
Offender Institutions. 
Inmate Information 
System
Cautions and out of 
court disposals for 
youths and adults. 
PNC 
Adult court orders. F20
Proven Reoffending 
Measure Input data (pre 
October 2017)
Adult prison releases 
(determinate). Inmate 
Information System
Adult prison releases 
(indeterminate) PPUD
Juvenile custodial 
releases from Youth 
Offender Institutions. 
P-nomis
Proven Reoffending 
Measure Input data 
(from October 2017)
Cautions and out of 
court disposals for 
youths and adults. PNC 
 Juvenile custodial releases 
from Secure Children Home’s 
and Secure Training Centres. 
eAsset
Adult prison releases 
(determinate and 
indeterminate)                  
Adult court orders. nDelius
Annex A 
 
Data sources pre-October 2017 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
October 2017 and beyond