Statistical News Release
A National Statistics Publication for Scotland
November 9, 2007
PRISON POPULATION PROJECTIONS, SCOTLAND, 2007-2008 to 2016-2017
The latest set of prison population projections, prepared in October 2007, show that the average daily prison population (excluding prisoners on home detention curfew) is projected to increase to 8,500 in 2016-2017. These projections take into account recent trends in the prison population, including final data for 2006 and the latest available data for the first 8 months of 2007.
The prison population in the first 8 months of 2007 has been higher than anticipated and this is reflected in the latest set of prison population projections, which project higher increases in the future population than the September 2006 projections. The current high prison population and the higher projected prison population is due to the increase in the average daily population of prisoners on remand (1,567 in 2006-2007 compared to 1,242 in 2005-2006).
The 2006-2007 average daily prison population which was projected to increase to 7,100 (rounded to nearest 100) reached 7,183. However, if early release on home detention curfew had not been introduced in July 2006, the 2006-2007 average daily prison population would have been higher.
Low risk prisoners sentenced to less than four years are eligible for release early from their sentences on Home Detention Curfew (HDC) where they are monitored by an electronic tag, have restrictions placed on their movements and can be returned to custody if the breach the conditions of their HDC. The average daily population of prisoners on HDC increased from 92 in July 2006 to 287 in November 2006 and has remained approximately 300 since then. If HDC had not been available then these prisoners would have been accommodated within prison.
Table 1 overleaf shows the prison population projections to 2016-2017. To show the total population that the Scottish Prison Service is responsible for and to estimate the impact if HDC was unavailable, we have assumed that the HDC population will remain at its current level and have added this estimate to the projected prison population. Note that the September 2006 projections did not take into account prisoners on HDC as there was insufficient data at that time (July and August 2006 figures only). Therefore cross year comparisons should be made using the first and fourth columns of table 1.
Issued by the Communications Branch of the Scottish Prison Service, Calton House, 5 Redheughs Rigg, Edinburgh EH12 9HW. For further information, call 0131-244 8476/8401(office); 244 8648 (fax); Pager number
01426 414 394; or E-Mail:James.O’Neill2@sps.gov.uk.
Table 1: Prison population projections for September 2006 and October 2007
September 2006 October 2007 Estimated HDC Projected plus
Projected Projected Population HDC population (1)7,100 7,183 (actual) 166 (actual) 7,348 (actual) 2006-2007
7,200 7,300 300 7,600 2007-2008
7,300 7,500 300 7,800 2008-2009
7,500 7,600 300 7,900 2009-2010
7,600 7,800 300 8,100 2010-2011
7,700 7,900 300 8,200 2011-2012
7,800 8,000 300 8,300 2012-2013
8,000 8,100 300 8,400 2013-2014
8,100 8,300 300 8,600 2014-2015
8,200 8,400 300 8,700 2015-2016
8,500 300 8,800 2016-2017
(1) Please note that the entries in this row may not add up exactly due to rounding.
NOTES FOR NEWS EDITORS
1. The prison population projections are not predictions or estimates, they are based on
extrapolation of past trends in the numbers entering custody and the sentencing trends
observed during the last 10-35 years. The projections do not depend on forecasts of crime
levels for the years ahead, as it is the sentencing behaviour of the courts which most
immediately determines the prison population. The projections assume that the
observed trends in sentencing behaviour will continue. If sentencing trends change in
the future these projections will not be realised.
2. Information on recent trends in the prison population in Scotland can be found in Annex A to
this news release. Details on the methodology used to produce the prison population
projections is described in Annex B.
3. Financial year information for 2006-2007 can be found in the Scottish Prison Service
Annual Report and Accounts for 2006-2007 (at
and in the Prison Statistics Scotland, 2006/07 bulletin (at
http://www.scotland.gov.uk/Publications/2007/08/31102446/0 ) .
4. Further information on Criminal Justice statistics within Scotland can be accessed at:
5. Official statistics are produced by professionally independent statistical staff – more
information on the standards of official statistics in Scotland can be accessed at:
RECENT TRENDS IN THE PRISON POPULATION
Final figures show that the average daily prison population reached its highest annual level of 7,183 during 2006/07, 5% above the previous annual high of 6,857 experienced during 2005/06.
Assessment of trends in the prison population in 2006 and the first 8 months of 2007 have been complicated by the fact that population levels over the last five years have failed to follow the usual seasonal pattern, as illustrated in Charts 1 and 2. Levels during March/April traditionally show a seasonal high, which follows a marked dip in the average daily population figures in December/January. This seasonal low reflects the holiday period and the reduced number of court sitting days. As Chart 1 illustrates, the population in 2004 did follow the earlier seasonal pattern, however, later years have not. In 2006, the population increased steadily from January 2006, despite the introduction, in July 2006, of early release on home detention curfew for low risk prisoners. The December 2006 population was 7,115, 247 above the figure for January 2006. Following a peak in March 2007, the prison population reached the highest ever recorded monthly daily average of 7,405 in August 2007 (provisional figures).
Chart 1: Average daily prison population, January 2004 – August 2007
Table 2 displays the monthly population figures from January 2005 to August 2007. It shows that the monthly average daily population figures for each month in 2006 were consistently higher than the corresponding months in 2005. The population figures for the first 8 months of 2007 are also higher than those for the first 8 months of 2006.
Table 2: Monthly average daily population figures – January 2005 to August 2007
2005 2006 2007 2006v2005 2007v2005 2007v2006
6,484 6,868 7,070 5.9% 2.9% Jan 9.0%
6,750 6,916 7,265 2.5% 5.0% Feb 7.6%
6,775 6,999 7,327 3.3% 4.7% Mar 8.2%
6,777 7,049 7,214 4.0% 2.3% Apr 6.4%
6,750 7,105 7,176 5.3% 1.0% May 6.3%
6,748 7,188 7,218 6.5% 0.4% June 7.0%
6,730 7,189 7,256 6.8% 0.9% July 7.8%
6,869 7,209 7,405 4.9% 2.7% Aug 7.8%
6,861 7,258 5.8% Sep
6,952 7,206 3.7% Oct
6,988 7,202 3.1% Nov
6,960 7,115 2.2% Dec
Average 6,792 7,111 4.7%
Chart 2 illustrates the pattern evident since January 2002, also distinguishing the different trends shown in the populations of remand, short term and long term prisoners. The monthly remand population in 2006 did not show the traditional seasonal pattern, remaining higher than recent years for all 12 months, with a substantial increase between January 2006 and September 2006, where the population reached a high of 1,621. In 2007, the monthly average daily remand population experienced a rapid increase between January 2007 and February 2007, from 1,604 to a high of 1,755. The population subsequently decreased to 1,547 in April 2007, increasing slightly to reach 1,614 in August 2007 The high and increasing remand population is the main reason that the prison population in 2007 has increased to record levels.
Chart 2: Average daily prison population, January 2002 – August 2007 (monthly)
Chart 2 also clearly shows the steady increase in the numbers of long-term prisoners up to May 2005, when they reached a peak of 2,944. The monthly average daily long term prison 2003
population then decreases steadily until April 2006 when it begins to slowly increase again. The monthly average daily long term population in April 2006 was just 2,807, increasing to 2,941 in December 2006. The monthly average daily long term population has remained at
2004about the same level for the first 8 months of 2007 and was 2,939 in August 2007.
The annual average short term population rose by 3% between 2005 and 2006. The increase
in the monthly average daily short term prison population occurred in the first 3 months of 2006,
2005when the population increased from 2,727 in January 2006 to 2,876 in March 2006. The
monthly average daily short term prison population then remained above 2,800 until August 2006 when it began to decrease, reaching 2,533 in January 2007, but has increased again to 2,852 in August 2007. The decrease from August 2006 to January 2007 in the short term prison
2006population was caused by the gradual introduction of early release on Home Detention Curfew rdfor low risk short term prisoners from 3 July 2006.
METHODOLOGY FOR PRODUCING THE PRISON POPULATION PROJECTIONS
1. The prison population is divided into different sentence and age groups as set out in Table A below, and we project the receptions of each of these groups separately. Female prisoners are not projected separately as numbers of women in custody are too small to be susceptible to the statistical techniques. The techniques used to project these receptions are described in paragraph 2. These receptions are then converted into population projections by allowing for the average time spent in custody by those in the relevant sentence band.
TABLE A: COMPONENTS OF THE PRISON POPULATION
Fine Defaulters N
Sentenced for less than 6 months Y
Sentenced for 6 months, less than 18 months Y
Sentenced for 18 months, less than 2 years Y
Sentenced for 2 years, less than 4 years Y
Sentenced for 4 years and over, excluding Life Y (1) N Life prisoners
Fine Defaulters N
Sentenced for less than 6 months Y
Sentenced for 6 months, less than 18 months Y
Sentenced for 18 months, less than 4 years Y
Sentenced for 4 years and over, excluding Life Y (1) Life/S205/S206 prisoners N
N Persons recalled from supervision/licence
(1) Receptions of life sentenced prisoners are no longer projected, refer to paragraph 6 for more details.
2. For each determinate direct sentence prisoner group, there is a choice of 6 separate receptions projections. Three are derived by linear regression estimated over, respectively, 1972-2006; 1983-2006 and 1997-2006. There are also three sets of projections derived from a different statistical technique, the seasonally-based Winters multiplicative method, estimated using monthly data over equivalent time spans but including the latest available monthly figures. The benefits of this latter technique are that, for the October 2007 projections, it enabled the use of monthly data up to August 2007, and the technique also avoids possible “discontinuities”
between the final year’s “actual” data and the first year of the projections. In each projection round, we assess which of the six alternative projection variants looks most “reasonable” in the light of the recent trends. The presumption is against any change of the choice of variant unless there seems fairly compelling evidence to justify this.
3. Remand receptions are projected to vary with the projected changes in direct sentenced receptions. Remands were higher than usual, on average, for the first 8 months of 2007. For this reason we used partial 2007 data on receptions to calculate the number of remand receptions per direct sentenced reception, and carried this forward through the projection period. The projected numbers of receptions for fine default were held constant at the level observed in 2006. Fine defaulters spend such short times in custody (around three days) that changes in the numbers of receptions would make very little difference to the resulting projected population. The projected populations of persons recalled from supervision/licence and “other” prisoners are calculated directly, so no projections of receptions are necessary.
4. With the exception of lifers, persons recalled from supervision/licence and “other”
prisoners, the projected receptions for each component are converted into population projections by allowing for the average time spent in custody by those in the relevant group. These “time served factors” are given in Table B below. The “time served factors” within some sentence length bands may appear rather lower than would be expected given that short-term prisoners must serve at least half of their sentence in custody. The reason is that time spent on remand counts towards this period. In addition, prisoners sentenced to less than four years can now be released early on Home Detention Curfew.
5. The projections of the population of prisoners recalled from supervision/licence assume that levels will vary with the eligible population i.e. those sentenced for 4 years or more. In 2006 the number of “recalls” in the prison population represented about 30% of the adult
population sentenced for 4 years and over, excluding Life. The number of “other” prisoners in
the prison population was held constant over the projection period, at the level observed in 2006.
6. Receptions of lifers ceased to be projected in 2004, due to changes in the way such prisoners are treated. In recent years, lifers have been eligible for parole once the punishment part of their sentence is served, and this has resulted in larger numbers of long-serving lifers being released than was previously the case. This change caused the previous projection method for lifer receptions to provide unrealistic estimates for the lifer population. So, the population of lifers is now projected on the basis of linear regression, based on lifer populations from 1995 to 2006.
TABLE B: TIME SERVED FACTORS USED FOR EACH COMPONENT OF THE PRISON
Component: Time Served Factor used in the
September 2007 projections
0.0691 25.22 Remand
Fine Defaulters 2.88 0.0079
Sentenced for less than 6 months 24.20 0.0663
Sentenced for 6 months, less than 18 months 101.98 0.2794
Sentenced for 18 months, less than 2 years 239.18 0.6553
Sentenced for 2 years, less than 4 years 1.1462 (1) Sentenced for 4 years and over, excluding Life2.9795
Life prisoners N/A
Fine Defaulters 2.19 0.0060
Sentenced for less than 6 months 21.97 0.0602
Sentenced for 6 months, less than 18 months 97.60 0.2674
Sentenced for 18 months, less than 4 years 319.01 0.8740 (1) Sentenced for 4 years and over, excluding Life 2.0953
Life/S205/S206 prisoners N/A
N/A Persons recalled from supervision/licence
(1) The time served factors are estimated by comparing the average daily population in the relevant sentence length group with the number of receptions for that group. In the case of young offenders sentenced for 4 years and over, excluding Life, this comparison is affected by the reclassification of young offenders to adult prisoners when they reach 21. In this case, the time served factor represents the time spent in custody before either release or reclassification. The time served factor for adults sentenced to 4 years and over, excluding Life are correspondingly increased to take account of this.
High and low variant projections of the prison population
As there is a choice of 6 separate receptions projections for each prisoner group (because we use 2 different projection methods and 3 different time periods) we also produce a high and low variant projection to illustrate the sensitivity of the projections to this choice of the receptions variants. The “High” variant is obtained by selecting in all cases the highest reception projection. The “Low” variant is equivalently derived by consistently selecting the lowest
reception projection. The resulting range of possible projections are illustrated in Chart 4 below.
Chart 4: Prison population projections to 2016-2017
Average Daily Population3000
1972-19731973-1974 1974-19751975-19761976-19771977-1978When the highest possible variants are used the prison population is projected to rise to 9,400 1978-19791979-19801980-1981in the year 2016-2017, this compares with 7,500 if the lowest possible variants are used. 1981-19821982-1983When compared with the figures prepared in October 2006, the projected population in 2015-1983-19841984-19852016 increased by 200 to 8,400, the low variant increased by 400 to 7,400 and the high variant 1985-19861986-1987decreased by 300 to 9,200. 1987-19881988-1989 1989-19901990-19911991-19921992-19931993-19941994-19951995-19961996-19971997-19981998-19991999-20002000-20012001-20022002-20032003-20042004-20052005-20062006-20072007-20082008-20092009-20102010-20112011-20122012-20132013-20142014-20152015-20162016-2017 10