U.S. Department of Justice    
Office of Justice Programs
Bureau of Justice Statistics
Special Report
Federal Justice Statistics Program

Time Served in Prison by Federal Offenders, 1986-97
June 1999, NCJ 171682

By William J. Sabol, Ph.D.
John McGready
The Urban Institute


In 1987 the Bureau of Justice Statistics (BJS) published
Sentencing and Time Served, reporting that Federal offenders who
had parole hearings between July 1979 and June 1980 and who had
been sentenced to 1 to 5 years in prison served about 2 years,
on average, or about 70% of the prison term imposed. ***Footnote 1:
Sentencing and Time Served, BJS Special Report, NCJ 101043, June
1987.***  Offenders who had received longer prison terms, while
incarcerated for a longer time, served a smaller proportion of
the prison term imposed -- about 50% for offenders sentenced to 5
to 10 years and less than 40% for those sentenced to more than
15 years.  

Beginning with the Sentencing Reform Act of 1984, however,
Federal sentencing and release practices underwent a series of
changes.  The act, which took effect on November 1, 1987,
established the Federal sentencing guidelines.  The guidelines
required a prison term for many offenses for which probation had
routinely been imposed and longer sentences for other offenses. 
The act also eliminated parole and reduced the amount of good
conduct time Federal offenders could earn.  As a result of what
are called "truth-in-sentencing" provisions of the act, Federal
offenders must serve at least 87% of the sentence imposed.

**********Highlights********

Sentences imposed

*Between 1986 and 1997 prison sentences for Federal offenses
increased from 39 months, on average, to 54 months.


Time to be served, 1986 and 1997

*The proportion of the sentence imposed that the offenders
entering Federal prison during 1986 would actually serve was
58%.  For those entering during 1997, it was 87%.

*Overall, time to be served increased from 21 months, on
average, for those entering Federal prison during 1986 to 47
months for those entering during 1997.

*Time to be served increased from 23 to 75 months for weapons
offenders, from 30 to 66 months for drug offenders, and from 74
to 83 months for bank robbery offenders. 

*Between 1986 and 1997 the number of Federal inmates serving a
term of imprisonment increased from 38,156 to 98,944. 
Approximately 65% of the increase in the Federal prison
population is attributable to an increase in the time served.

Time served to first release

*For those released from Federal prison, time served increased
from 15 months, on average, during 1986 to 29 months during 1997.

*Time served increased from 19 months to 40 months for weapons
offenders, from 20 months to 43 months for drug offenders, and
from 55 to 60 months for bank robbery offenders.

*********************

Between 1986 -- the year before implementation of the Sentencing
Reform Act -- and 1997, imposed prison terms increased from 39
months to 54 months.  Further, during this period, the proportion
of the imposed prison term that offenders could expect to serve
increased from 59% to 87%.  The time offenders entering Federal
prison could expect to serve increased from about 21 months, on
average, during 1986 to about 47 months during 1997. 

Those convicted of an immigration or weapons offense experienced
the greatest relative increase in time to be served in Federal
prison.  The time to be served for immigration offenders increased
from 3.6 months to 15.1 months, and for weapons offenders, from 23
months to 74.5 months.  For drug offenders the increase was from
29.7 months to 66.2 months.

Not only did these changes affect individual offenders, but they
also substantially affected the Federal prison population.  The
population increased nearly threefold from 38,156 in 1986 to 98,944
in 1997 (figure 1). About 60% of this increase can be attributed to
the increase in time to be served by new court commitments; 25%, to
the increase in the number of suspects investigated by U.S. attorneys;
and 15%, to the increase in the proportion of offenders sentenced to
prison. Decreases in the prosecution rate and in time served by
supervision violators curtailed the growth of the prison population.

Changes to Federal sentencing policy have been accompanied by
changes at the State level.  The Violent Crime Control and Law
Enforcement Act of 1994 authorized incentive grants to States
that adopted truth-in-sentencing laws requiring offenders
convicted of violent crimes to serve at least 85% of the imposed
sentence in prison. ***Footnote 2: See, Office of Justice Programs,
Violent Offender Incarceration and Truth-in-Sentencing Incentive
Grants: Program Guidance and Application Kit, FY1998, NCJ 168942
(1998).*** Since 1994, 27 States and the District of Columbia have
adopted the Federal requirement. Additionally, 13 States have
adopted laws that require offenders to serve a specific proportion
of the sentence imposed, albeit less than 85%.  Fourteen States have
abolished parole.  ***Footnote 3: Truth in Sentencing in State Prisons,
BJS Special Report, NCJ 170032, February 1998.***


*************************
Differences between entry 
and release cohorts
*************************

Different conclusions about the impact of sentencing policies on
time served can be drawn, depending on whether entry or release
cohorts are observed. (A cohort is a group of persons having a
common characteristic, like a birth year or a particular year of
entering or leaving prison.)     

For measuring the effects of changing sentencing policies on
length of stay, expected time to be served by the entry cohort
has advantages over time actually served by the release cohort. 
Because the effects of sentencing reforms can be observed almost
immediately in sentences imposed, expected time to be served by
an entering cohort can provide a direct measure of the effects
of reforms as they are implemented.  

Actual time served by release cohorts may reflect a range of
policies in effect during the years when cohort members entered
prison.  No single exit cohort represents offenders sentenced at
the time a reform was implemented.  To show the effects of
reforms on length of stay, complex adjustments to exit cohort
data would be needed to make them representative of entry
cohorts.  

In accounting for relatively recent changes in sentencing,
release cohorts are more likely to contain offenders who
received shorter sentences and less likely to contain those with
longer sentences.  As a result, time served by release cohorts
may understate the  effects of sentencing reforms designed to
increase lengths of stay even as prison terms increase.    

During 1986, the year prior to implementation of the Sentencing
Reform Act of 1984, 16% of offenders entering prison received
prison sentences of more than 5 years.  About 11% of the release
cohort in that year were released from sentences of more than 5
years (not shown in a table).  By 1997, 26% of the entering
cohort received sentences of more than 5 years, and 18% of the
exiting cohort were released from prison sentences of more than
5 years. 

By offense group, the distribution of sentences in the entering
and exiting cohorts varied.  For example, 13.2% of the violent
offenders released during 1997 were released from sentences of
longer than 10 years, and 20.2% of the violent offenders entering
during 1997 had sentences of more than 10 years. For drug offenders,
7.7% of the releases in 1997 had sentences of more than 10 years,
while 18.3% of the drug offenders entering prison had sentences of
more than 10 years.

*************************************
Measuring length of stay for 
entering cohorts of Federal prisoners
*************************************

To measure the effects of the Federal sentencing legislation on
time to be served, data from entering cohorts of prisoners are
used.  Time to be served is the amount of time that offenders
who enter prison on a U.S. district court commitment in a given
year serve before their first release from prison.  Time to be
served by offenders entering Federal prison is based on a
combination of actual data on time served for offenders who were
also released during the study period and estimates of time to
be served for those who had not been released.

During 1986-97, 383,108 offenders  entered prison from a U.S.
district court commitment.  Actual time served is observed for
the 72% who were released at some time before the end of the
study period on December 31, 1997 (appendix table on page 14).  
For offenders who entered before 1993, more than 80% were
released by yearend 1997; for the 1995 entering cohort, more
than 53% were released.

Actual time served is not available for  two categories of
offenders who had not been released from prison:  those
sentenced pursuant to the Sentencing Reform Act of 1984 (new law
offenders) and those sentenced under laws in effect before that
act (old law offenders). New law offenders are given determinate
sentences and can receive up to 54 days of good conduct credit
for each year served without incident for sentences longer than
1 year.  Those sentenced to 1 year or less are not eligible for
good-time credits.  Time to be served for new law offenders still
in prison was estimated to be the sentence imposed less the maximum
good conduct credit the offenders could possibly earn.

Time to be served for old law offenders still in prison was
estimated from the average stay for released old law offenders,
taking into account the offense.  


***********************************
Offenders sentenced pursuant to the
Sentencing Reform Act of 1984
***********************************

The provisions of the Sentencing Reform Act of 1984 applied to
offenders who committed their crimes on or after November 1, 1987.
Offenders sentenced pursuant to this act are often called "new law"
offenders, while those subject to laws in effect before the act are
often called "old law" offenders.
 
The first cohort of offenders sentenced pursuant to the Sentencing
Reform Act entered Federal prison during 1988.  During 1988, 23% of
the 24,591 commitments were new law offenders.  During the following
year, 62% of U.S. district court commitments were new law offenders.  
By 1997 almost all (99.5%) of the 38,375 offenders entering Federal
prison were sentenced pursuant to the Sentencing Reform Act.

Cohorts of first releases from Federal prison lagged entering cohorts
by 2 years or more in their proportion of new law offenders.  During
1989, 29% of first releases were new law offenders, as compared to the
62% of U.S. district court commitments.  By 1995 more than 90% of
released defendants were new law offenders.

***********************************************
Time to be served by Federal offenders, 1986-97
***********************************************

Offenders entering Federal prison

Beginning with the Sentencing Reform Act of 1984, sentencing and
release practices in the Federal system underwent a series of
changes -- abolishment of  parole, required completion of 87% of
the imposed sentence in prison, and Federal sentencing guidelines.
A series of mandatory penalties was established, most notably for
drug offenders and for offenders using a weapon to commit an offense.
As a result of these sentencing reforms, prison terms imposed on
offenders entering Federal prison on a U.S. district court commitment
increased from 38.9 months during 1986 to 53.9 months during 1997 
(table 1).


Table 1.  Average time to be served by offenders entering Federal prison, 

                         Months of imprisonment
                           Term       Time           Proportion of 
     Year       Number     in effect  to serve       sentence to serve

      1986      25820       38.9 mo     20.7 mo             58.2%
      1987      26684       42.6        23.1                58.0
      1988      24591       46.3        26.9                61.6
      1989      28249       42.1        30.3                74.3
      1990      33124       43.4        34.7                81.1
      1991      32812       46.9        38.8                83.5
      1992      34161       51.5        43.2                84.6
      1993      37065       53.4        45.4                85.3
      1994      34407       54.1        46.3                85.7
      1995      32566       53.8        46.4                86.0
      1996      35254       56.0        48.7                86.6
      1997      38375       53.9        46.9                86.7

Notes:  Represents offenders committed to prison by U.S. district courts.
Average sentence length excludes offenders sentenced to life or death sent
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


Prior to the implementation of the Sentencing Reform Act of
1984, Federal offenders could expect to serve about 58% of the
sentence imposed by the court.  A 39-month prison sentence
translated into about 21 months to be served in prison.  By
contrast, following the implementation of the Sentencing Reform
Act, an offender who received a 39-month prison sentence could
expect to serve 34 months.

As a consequence of changes in the time served requirement and
increases in the sentences imposed by the Federal courts, time
to be served for offenders entering Federal prison nearly doubled
between 1988 and 1997, increasing from 26.9 months to 46.9 months.

Prior to the implementation of Federal sentencing reforms, more
than 50% of offenders entering Federal prison were released
after serving a year or less in prison, and 70% were released
after serving 2 years or less (figure 2).  By contrast, about
a quarter of offenders entering Federal prison during 1997
were released after serving a year or less.  About 5 years will
pass before 70% of those entering during 1997 are released.

Following the elimination of parole and the requirement that
Federal offenders serve at least 87%, the proportion of the
sentence to be served by the entering prison cohort increased
from about 58.2%, on average, to 86.7% (figure 3).  As the
proportion of prison commitments sentenced pursuant to the
Sentencing Reform Act approached 100% during 1996-97, the
proportion of the sentence to be served by Federal offenders
approached 87%.

*********************
Offense of conviction
*********************

Except for property offenses, time to
be served increased for each major offense category. 
Immigration and weapons offenses experienced the greatest
relative increase in time to be served.  For immigration
offenders time to be served increased from 3.6 months during
1986 to 15.1 months during 1997 (table 2).  For weapons
offenders time to be served increased from 23 months to 74.5
months.  Time to be served more than doubled for drug offenders,
increasing from 29.7 months to 66.2 months. 


Table 2. Average time to be served by offenders entering Federal prison,
by offense of conviction, 1986-97

                           Average time to be served (in months)
         All             Violent           Property                      Public-order
Year     offenders    Any     Robbery    Any     Fraud    Drugs    Any    Weapons Immigration

    1986     20.7 mo  65.2 mo  73.5 mo  18.4 mo  16.9 mo  29.7 mo   9.3 mo  23.0 mo   3.6 mo
    1987     23.1     69.5     75.3     17.0     15.9     31.9     11.2     27.9      3.6
    1988     26.9     65.9     72.2     17.2     16.5     39.3     13.2     32.4      4.1
    1989     30.3     59.2     66.7     14.9     14.8     48.1     13.7     42.3      3.7
    1990     34.7     66.2     74.0     14.9     15.2     57.8     13.5     46.1      3.6
    1991     38.8     69.6     79.6     16.2     16.3     61.0     16.8     47.4      4.6
    1992     43.2     74.8     84.6     16.6     17.1     62.7     23.4     56.0      5.4
    1993     45.4     77.3     84.6     17.4     17.9     62.8     27.1     62.3      7.3
    1994     46.3     82.0     89.9     18.0     17.1     65.4     27.4     67.1      9.5
    1995     46.4     85.0     93.5     17.5     18.0     67.8     28.1     68.8     11.0
    1996     48.7     80.3     90.5     18.1     18.3     69.4     31.8     73.7     13.9
    1997     46.9     76.1     82.6     17.8     18.2     66.2     30.8     74.5     15.1

Notes:  Represents offenders committed to Federal prison by U.S. district courts.
Excludes offenders sentenced to life in prison or to death.
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


For drug offenses the sharpest increase in time to be served
followed the implementation of the Sentencing Reform Act of 1984
during 1987 and antidrug legislation enacted during 1986 and
1988.  Between 1987 and 1990, time to be served for drug
offenders increased from 32 to 58 months.  While time to be
served continued to increase after 1990, the rate of increase
slowed, increasing to 66.2 months during 1997.

For weapons offenses time to be served also increased almost
immediately following implementation of the Sentencing Reform
Act, doubling from 23 months during 1986 to 46 months during
1990.  However, by contrast to drug offenses, time to be served
for weapons offenses continued to increase following additional
statutory increases in the Omnibus Crime Control Act of 1990,
rising to 74.5 months during 1997.


For immigration offenses time to be served increased most
dramatically following amendments to the Federal sentencing
guidelines for immigration offenses implemented on November 1,
1991.  These amendments provided for sentence enhancements based
on the number of aliens smuggled or the amount of trafficking in
false nationality documents.  During 1991 time to be served for
immigration offenses was 4.6 months, on average.  Following the
amendments, time to be served increased to 15.1 months during
1997.

****************************
Reduction of sentences based
on substantial assistance
****************************

At the time of sentencing or up to 1 year after sentencing,
district courts can grant reductions in sentences for
substantial assistance to the Government.  Pursuant to *5K1.1
of the Federal sentencing guidelines, the Government may file a
motion at sentencing to reduce the sentence in exchange for the
defendant's assistance to the Government.  During 1996 U.S.
district courts granted 7,845 substantial assistance departures.
About two-thirds of the departures were granted to drug
offenders.*   ***Note: U.S. Sentencing Commission, 1996
Annual Report.***

Rule 35(b) of the Federal Rules of Criminal Procedure also
provides for reductions in sentences for offenders providing
substantial assistance. The Government can file motions to
reduce the sentence within 1 year of sentence imposition.
Resentencings under Rule 35(b)increased from 27 such cases in
1988, the first year of applicability, to 1,536 in 1993, before
decreasing to 1,076 in 1996.

Offenders who entered prison during 1991 and 1992 and who were
resentenced under Rule 35(b) had their sentences reduced by
about 46 months, on average -- from about 116 months to 70 months.


Offenders resentenced pursuant to Rule 35(b) after providing substantial
assistance to the Government, 1988-96

                  Average sentence imposed
                                       Amount of
    Year    Number Original     New    reduction
    1988       27     94.1 mo   60.7 mo  33.3%
    1989      219    125.5      81.5     44.0
    1990      509    123.5      78.7     44.8
    1991      818    118.1      72.3     45.8
    1992     1078    116.2      70.3     45.9
    1993     1536    111.9      68.4     43.6
    1994     1340    104.7      65.6     39.1
    1995     1025     98.2      60.8     37.4
    1996     1076     97.3      61.2     36.1

Data source:  Federal Bureau of Prisons, SENTRY data file, annual.

While time to be served for violent offenses increased following
Federal sentencing reforms, it increased at a lesser rate. 
Between 1986 and 1997, time to be served for violent offenses
increased from 65.2 months to 76.1 months.  For robbery
offenses, time to be served increased from 73.5 months to 82.6
months.

By contrast to other offenses, time to be served for property
offenses decreased slightly from 18.4 months during 1986 to 17.8
months during 1997.

**************************************
Offenders released from Federal prison
**************************************

As time to be served by offenders entering Federal prison
increased, time served by released offenders also increased
between 1986 and 1997 -- from 14.5 months to 28.8 months (table
3).  In contrast to offenders entering Federal prison, offenders
released had been sentenced on average to substantially shorter
prison terms.  


Table 3.  Average time served by offenders released from Federal prison, 1986-97

                            Months imprisonment                                    
    Year   Number      Term in       Time served       Percent of
                       effect        to first release  term served
    1986    21661       27.3 mo             14.5 mo      59.2
    1987    23319       27.5                15.0         59.4
    1988    22781       32.0                17.2         58.8
    1989    22951       33.4                18.1         59.6
    1990    26379       29.9                17.2         64.6
    1991    25771       31.8                19.4         70.7
    1992    25452       30.8                20.4         76.6
    1993    26503       32.6                22.9         79.9
    1994    28410       32.3                24.1         82.8
    1995    27902       33.9                26.4         84.5
    1996    30264       35.0                28.2         86.6
    1997    31894       34.9                28.8         86.7

Notes: Represents offenders committed to prison by U.S. district courts.  Average
sentence length excludes offenders sentenced to life in prison or to death.
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.




Offenders committed to Federal prison during 1986 received a
sentence of 38.9 months, on average, whereas those released
during 1986 had received a sentence of 27.3 months.  On average,
offenders committed during 1997 received a sentence of 53.9
months, whereas those released had received a sentence of 34.9
months.

Time served by offenders released from prison reflects sentences
imposed over several years rather than one, and to a greater
degree than occurs among offenders entering prison, the release
cohort represents offenders sentenced to shorter terms of
imprisonment.  During periods of transition, such as the 10
years following implementation of the Sentencing Reform Act,
actual time served by offenders released from prison understates
the impact of sentencing reforms.

The proportion of the sentence served by offenders released from
Federal prison also increased following implementation of the
Sentencing Reform Act -- increasing from 59.2% during 1986 to
86.7% during 1997 (figure 4).  Compared to commitments to
Federal prison, fewer released prisoners had been sentenced
pursuant to the Sentencing Reform Act .  (See Box: Offenders
sentenced pursuant to the Sentencing Reform Act of 1984)

Consequently, the average sentence served exceeded 80% of the
imposed sentence about 5 years later for the release cohort than
for the entry cohort.


***********************
Offenders committed to
Federal prison for life
***********************

Between 1986 and 1997 the number of offenders annually committed
to Federal prison with a sentence of life imprisonment increased
from 36 to 314 (table). Ninety percent of these offenders, those
who were sentenced pursuant to the provisions of the Sentencing
Reform Act of 1984, are not eligible for release on parole. 
Federal law, however, permits the Bureau of Prisons to release
offenders sentenced to life imprisonment if they are at least age
70 and have served at least 30 years.*
***Note: 18 U.S.C. * 3582(c)(1)(A)(ii).***

Old law offenders committed to Federal prison for life are
eligible for parole at the discretion of the U.S.  Parole
Commission.  Between 1986 and 1997, 93 offenders committed to
Federal prison for life were released on parole after almost 16
years in prison (not shown in a table).


            Number of Federal 
            prisoners with a 
            sentence of life
    Year    in prison or death

    1986          36
    1987          43
    1988          32
    1989          48
    1990          82
    1991         109
    1992         194
    1993         252
    1994         295
    1995         233
    1996         261
    1997         314

Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


*********************
Offense of conviction
*********************

Except for property offenders, time served by offenders released
from Federal prison increased for all major offense categories
(table 4).  Similar to offenders entering Federal prison, time
served by immigration, drug, and weapons offenders increased at
the greatest rate.  For immigration offenses time served
increased from 3.5 months during 1986 to 10.9 months during 1997.
For drug offenses, time served increased from 20.4 months to 42.5
months.  And for weapons offenses, time served increased from 18.6
months to 40.3 months.


Table 4.  Average time to be served by offenders released from Federal prison, 
by offense of conviction, 1986-97
                                         Average time to be served (in months)
         All             Violent              Property                         Public-order
Year     offenders   Any        Robbery     Any     Fraud     Drugs      Any    Weapons  Immigration

1986     14.5 mo    48.8 mo     54.8 mo    15.5 mo  13.2 mo   20.4 mo    6.4 mo  18.6 mo   3.5 mo
1987     15.0       48.2        55.3       15.1     12.5      21.2       6.6     18.4      3.7
1988     17.2       50.8        58.3       15.8     13.7      22.6       8.3     19.7      4.2
1989     18.1       49.8        59.4       16.1     14.5      25.1       8.5     19.7      4.1
1990     17.2       51.0        60.3       15.6     14.2      26.4       7.3     18.9      3.6
1991     19.4       53.5        60.5       15.8     14.5      28.1       8.6     19.6      3.9
1992     20.4       51.8        60.8       15.7     14.8      28.6      10.0     19.3      4.9
1993     22.9       53.8        61.6       15.4     15.2      32.0      12.1     22.8      5.5
1994     24.1       51.5        59.2       15.3     14.8      33.9      13.1     26.4      5.9
1995     26.4       50.9        57.2       15.7     15.6      37.6      14.7     31.4      6.9
1996     28.2       53.7        59.8       15.6     15.5      40.3      17.2     37.9      8.3
1997     28.8       53.3        59.7       15.3     15.6      42.5      17.9     40.3     10.9


Notes: Represents defendants released by normal means following a commitment by a U.S. district court.
Excludes offenders sentenced to life in prison or death.
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.



The average time served for property offenses remained virtually
constant throughout the 1986 to 1997 period.  In 1986 the average
time served by property offenders was 15.5 months; in 1997 it was
15.3 months. Offenders released from prison under sentences for
fraud experienced less than a 3-month increase in the actual
average time served, from 13.2 months to 15.6 months.


***************************
Extraordinary releases from
Federal prison, 1986-97
***************************

Offenders can be released from prison following expiration of
the sentence, completion of term with good time credits, release
onto parole, or by an "extraordinary" means such as death,
treaty transfers, commutation of sentences, termination of
sentence ordered, and having the sentence vacated.  In addition,
in 1994 the Violent Crime Control and Law Enforcement Act
permitted the early release of nonviolent offenders who
successfully completed a drug treatment program.  Offenders
successfully completing a drug treatment program may have their
terms reduced by up to 1 year.


              Method of extraordinary release
              Drug               Termination
Year   Total  treatment   Death  order*     Other

 1986     377        0       55       233      89
 1987     424        0       78       248      98
 1988     393        0      100       221      72
 1989     420        0       92       258      70
 1990     510        0      110       291     109
 1991     502        0      122       287      93
 1992     699        0      120       317     262
 1993     656        0      146       301     209
 1994    1021        0      175       376     470
 1995     769       73      195       308     193
 1996    2178      852      210       428     688
 1997    2814     1689      212       239     674

*Includes sentence commutation.
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


Between 1986 and 1997 the number of offenders released by
extraordinary methods increased from 377 to 2,814.  Following
the introduction of early release after drug treatment, the
number of extraordinary releases increased from 769 in 1995 to
2,178 in 1996 and to 2,814 in 1997 (table).


Before 1996 most extraordinary releases were for sentence 
commutation or a termination order -- between 40% and 60% of
extraordinary releases -- or because the offender died -- between
15% and 26%.  By 1997 releases for successful completion of drug
treatment accounted for 60% of extraordinary releases.

Time served to first release by those released by extraordinary
means followed a different pattern than it did for offenders
released by normal means.  Average time served for extraordinary
releases was about 11 months in 1986 (not shown in a table), or 
about 3 months less than the average time served by normal releases.  
By 1997 average time served by extraordinary releases reached
about 42 months, or about 13 months longer than the average time
served by normal releases.

Extraordinary releases by definition leave prison before serving
their expected terms. Consequently, the average percentage of term
served by extraordinary releases is lower than that served by normal
releases.  Between 1986 and 1997 the percentage of term served
by extraordinary releases increased from about 30% to almost 65%
(not shown in a table).  By comparison, normal releases served
about 60% of their terms before release in 1986 and about 87% in 1997.


*****************
Time to be served
*****************

Following implementation of Federal sentencing reforms, time to
be served by offenders entering Federal prison increased from
20.7 months during 1986 to 46.9 months during 1997.  Truth in
sentencing led to substantial increases in time to be served by
increasing the proportion of sentence to be served.  Increases
in sentences imposed -- largely the result of mandatory minimum
prison terms -- led to a slight increase in time to be served by
Federal offenders.  Changes in the composition of offenders
prosecuted and in the Federal sentencing guidelines also led to
an increase in the proportion of offenders sentenced to prison.

Truth in sentencing, increased sentences, and more offenders
being sentenced to prison impacted the overall time to be served
in diverse amounts.  The truth-in-sentencing provisions of the
Sentencing Reform Act of 1984 that require offenders to serve at
least 87% of the sentence imposed, when applied to the increases
in sentences imposed, accounted for about 61% of the 26-month
increase in time to be served by Federal offenders (table 5). 
The increases in prison terms alone accounted for about 19% of
the overall increase, and larger numbers of offenders sentenced
to prison accounted for an additional 19%.


Table 5.  Factors contributing to the increase in the time
to be served by Federal offenders

                            Proportion of increase due to --
                                        Proportion of
                              Sentence  sentence to  Offenders
Offense of conviction   Total imposed   be served    sentenced

Total                    100%     19%       61%       20%
Violent offenses           3      -5         8         0
 Robbery                   2      -5         6         1
Property offenses         -3      -6         5        -2
 Fraud                     3      -2         2         2
Drug offenses             77      11        32        33
Public-order offenses     23      18        16       -11
 Weapons                  12       3         4         5
 Immigration               6      11         2        -6
Unknown offenses           0       1         0        -1

Notes:  Totals may not equal the sum of the components due to rounding.
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


The increase in time to be served by Federal offenders can be
apportioned across offense categories.  Among the major offense
categories, the increase in time to be served by drug offenders
accounted for 77% of the increase in time to be served by all
Federal offenders.  Changes in time to be served by public-order
offenders accounted for an additional 23% of the overall
increase.  The proportion of the increase attributable to
violent offenders (3%) was offset by the decrease in time
to be served by property offenders.

Among public-order offenders the increase in time to be served
by weapons offenders accounted for more than half the increase,
while the increase for immigration offenders accounted for about
a quarter of the total increase in the overall category.  

Truth in sentencing, mandatory minimums, and the Federal
sentencing guidelines affected different offenses to varying
degrees.  For some offense categories these factors led to an
increase, while for others, a decrease.  

For drug offenses the increase in time to be served was
attributable in equal parts to the requirement that Federal
offenders serve at least 87% of the sentence imposed and the
increase in the proportion of drug offenders sentenced to
prison.  By contrast, for public-order offenses the change in 
the proportion of offenders sentenced to prison did not
result in an increase in time to be served.  Instead, the
increase was the result of the increase in sentences imposed
and in the proportion of sentence to be served.

*****************
Prison population
*****************

Between 1986 and 1997 the number of offenders serving a
sentence in Federal prison increased from 38,156 prisoners
to 98,944 prisoners (figure 4).  While the number of offenders
in each major offense category increased, the number of 
offenders incarcerated for a drug offense increased the most --
from 14,976 to 58,610 prisoners (table 6). Drug offenders
accounted for about 72% of the increase in the Federal prison
population.  Public-order offenders accounted for 22% of the
increase; violent offenders, 4%; and property offenders, 1%.


Table 6.  Federal prison population, by offense of conviction, 1986-97

                                   1986                     1997
Offense of conviction       Number     Percent       Number    Percent

      All offenses           38156      100.0%        98944    100.0%

Violent offenses              9401       24.9%        11658     11.9%
 Robbery                      6507       17.2          8464      8.7
 Other violent                2894        7.7          3194      3.3

Property offenses             7342       19.4%         8151      8.4%
 Fraud                        2451        6.5          5280      5.4
 Other property               4891       12.9          2871      2.9

Drug offenses                14976       39.6%        58610     60.0%

Public-order offenses         6084       16.1%        19197     19.7%
 Weapons                      1611        4.3          8082      8.3
 Immigration                  1496        4.0          5454      5.6
 Other public-order           2977        7.9          5661      5.8

Unknown offenses               353                     1328


Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


Eight factors can be shown to be associated with the growth in
the Federal prison population between 1986 and 1997.  Some
factors impacted the number of offenders sentenced to Federal
prison while other factors impacted the number offenders
returning to prison following a supervision revocation.

Factors impacting offenders sentenced to Federal prison --  

* investigations by U.S. attorneys increased from 80,613 to
98,454 

* prosecutions by U.S. attorneys increased from 54,222 to 64,856  

* defendants convicted increased from 43,920 to 56,670 

* defendants incarcerated increased from 23,058 to 39,431       
  
* time to be served increased from 20.7 months to 46.9 months.

Factors impacting offenders returning following a supervision
revocation --  

* offenders under Federal community supervision increased from
71,361 to 90,751          

* supervision violations increased from 7,299 to 13,217          

* time served for supervision violations decreased from about
10.4 months to 6.8 months.

The primary factors that resulted in the increase in the Federal
population were increases in time to be served, investigations
by U.S. attorneys, and the incarceration rate.  Almost two-thirds 
of the increase in the Federal prison population can be
attributed to the increase time to be served by Federal
offenders (table 7).  About a quarter of the increase can be
attributed to the increase in investigations by U.S. attorneys. 
Fifteen percent of the increase is attributable to the higher
rate at which Federal offenders were sentenced to prison, as
measured by the ratio of prison commitments to convictions.
Additionally, increases in the number of offenders convicted of
Federal offenses, increases in the number of offenders under
Federal community supervision, and the revocation rate also
caused the Federal prison population to increase between 1986
and 1997.


Table 7.  Factors contributing to the increase in the Federal prison population, 1986-97

                                          Change in prison       Change in number of inmates due to
                                            population             offense-specific changes
                                        Number of
Component of change:                    inmates     Percent   Violent   Property   Drugs  Public-order

        Total                               60788     100%      3441      1280     42925     12913
Suspects in matters concluded               15507    25.9       3970      1345     11017      -825
Defendants in cases terminated              -6267   -10.5      -3045     -1358     -3141      1277
Defendants convicted                         2939     4.9        997       150      1070       722
U.S. district court commitments              9182    15.4        816      1092      3461      3813
Length of stay for district court commits   39199    65.5        704        51     30518      7926
Offenders under supervision                  2142     3.6        551        47      1475        69
Supervised release violators                 3282     5.5        605      1243       467       967
Length of stay for release violators        -6171   -10.3      -2339     -1762     -1234      -836


Notes:  Offense-specific columns do not add up to total change in prison population
because they exclude offenders whose offenses are unknown.
Data source:  Federal Bureau of Prisons, SENTRY data file, annual.


But for two of the factors measured, the Federal prison
population would have increased to a greater extent.  The slight
decrease in the prosecution rate -- as measured by the ratio of
prosecutions to investigations -- from 67.3% of suspects
investigated to 65.9%, and the decrease in time served by
supervision violators from 10.4 months to 6.8 months, curtailed
the growth of the prison population by more than 12,000 inmates.

The eight factors affected different offense categories to
varying degrees.  The increase in time to be served was the
primary cause for the increase in the number of drug and
public-order offenders in Federal prison:  about 71% of the
increase in drug offenders and 61% of the increase in
public-order offenders were attributable to the increase in time
to be served.  By contrast, time served was associated to a
lesser extent with the increase in the number of offenders
incarcerated for property and violent offenses: about 20% of the
increase in violent offenders and 4% of the increase in property
offenders were attributable to the increase in time to be served.

The increase in the number of property offenders, though small
in comparison to the increase in the number of offenders
incarcerated for drug and public-order offenses, was
attributable a variety of factors.  Unlike other offense
categories, the increase in the proportion of offenders
sentenced to prison was a dominant factor.  When other factors
are controlled for, 85% of the increase in the number of property
offenders incarcerated was attributable to the increase in the
incarceration rate.


***********
Methodology
***********

Data sources

The source of data for tables presented in this report is the
BJS Federal Justice Statistics Program database.  The database
is constructed from source files provided by the Executive
Office for the U.S. Attorneys, the Administrative Office of the
U.S. Courts, the U.S. Sentencing Commission, and the Federal
Bureau of Prisons.  

Data tabulations, except where otherwise indicated, were
prepared from contractor analyses of the source agency datasets
indicated. 


The data for prison populations include only those inmates
serving a term of imprisonment resulting from a conviction or a
supervision violation.  Arrestees, boarders, and other detainees
are excluded.

Measuring time served 
and time to be served

This report uses several measures of length of stay, and it relies
on two similar decomposition methods to calculate the degree to
changes in length of stay and changes in the yearend prison population
can be attributed to several factors.  In addition, it uses concepts
that sound similar but have different meanings. This appendix addresses
these matters.

*********************
Prison term in effect
*********************

Term in effect or prison term is the operative length of sentence
after adjustments and credits, including jail credits, have been
applied to the sentence imposed by the district court.  For
offenders sentenced to a single sentence, the term in effect is
equal to the length of the single sentence imposed.  For offenders
sentenced to more than one sentence, term in effect is determined
by whether the sentences are to be served concurrently or consecutively. 
If sentences are concurrent, then term in effect equals the
longest sentence imposed.  If sentences are consecutive, term in
effect equals the sum of the sentences imposed minus any portion
of any sentence that is to be served concurrently with another
sentence.  These determinations of term in effect also assume
that all postsentence adjustments to a sentence have been made. 
Most commonly, postsentence adjustments include Rule 35
resentencings, including Rule 35(b) reductions for substantial
assistance.

***********
Time served
***********

The measures of time served are defined for the
cohort of persons entering prison during a year and the cohort
of persons released from prison during a year.  For persons
entering Federal prison, time to be served is measured by
expected time or the number of months that an offender can
expect to serve until first release.  For offenders released
from prison, time served is measured as the number of months
actually served, which is the difference between the release
date and the commitment date plus adjustments for jail credits.   

For each cohort of prisoners entering Federal prison following a
U.S. district court commitment, expected time to be served is
the average number of months of their prison term that members
of the cohort can expect to serve before release from prison. 
This measure includes the jail time credited toward sentences. 
For members of entering cohorts who have been released from
prison, time until first release is measured as actual time
served plus jail credits.  For offenders still in prison, time
until first release is estimated as follows --

* for new law offenders sentenced to terms of less than or equal
to 1 year, time to be served is the prison term imposed

* for new law offenders sentenced to more than 1 year, time to be
served is 87% of the prison term imposed 

* for offenders sentenced under old law, time to be served is the
offense-specific average amount of time actually served by old
law offenders who were released from prison.  Each offender in a
given offense category is given the offense category's average
based on all members of the category who had actually been
released.  This method will underestimate time to be served for
old-law offenders still in prison, as these remaining prisoners
will have served longer than average times before they are
released.

Excluded from analyses of time to be served are (1) offenders
sentenced to a term of life imprisonment or death and (2)
offenders who were released by extraordinary methods such as
commutation or death.

*************************
Proportion of term served
*************************

Proportion of term served is a measure of truth in sentencing;
it measures the degree to which prison sentences served
correspond to the sentence imposed. Proportion of term served
is measured relative to the prison term in effect.

Proportion of term served is calculated on and reported only
for terms of imprisonment greater than 1 year.  New law
offenders sentenced to terms of less than 1 year are not
eligible for good-time reductions.  As the percent of term
reported is the average of each individual's percent of term
served, the relatively large number of prison terms of less
than or equal to 1 year would raise the average percent of
term served and provide a biased measure of truth in sentencing.
For example, in 1995, the average percent of term served for
all prisoners released from a U.S. district court commitment
was about 90%.  However, for those offenders released from
terms of greater than 1 year, it was 85%.  About 30% of the
prisoners released during 1995 were released from terms of 1
year or less; the average percent of term served for these
short sentenced prisoners was 100%. 

For entering cohorts of prisoners, percent of term served is the
ratio of time until first release to prison term in effect.  The
term in effect is the operating prison term or sentence, and it
may differ from the imposed sentence as it reflects postsentence
adjustments or changes.  For exiting cohorts of prisoners,
percent of term served is the ratio of actual time served to the
prison term in effect.

For exiting cohorts, percent of term excludes offenders released
by extraordinary methods, such as treaty transfer, termination
order or commutation, death, or early release for completion of
drug treatment. 

Decomposition methods

Changes in time served and the yearend prison population are
analyzed using methods that apportion the change in each
quantity into several components or factors that are responsible
for the changes.  Each decomposition begins with an identity
that defines the relationship under investigation.  As this
identity holds for each period, it can be written for each
period that is compared.  To evaluate the changes between
periods, the identity in the first period is subtracted from the
identity in the second period.  The differences are applied to
the levels of each factor in the identity. 

***************************************
Decomposing changes in time until first
release for the entering cohorts
***************************************

The change or difference in time until first release
between the 1986 and 1997 entry cohorts is decomposed
into the offense-specific portions due to changes in
terms imposed, changes in the proportion of term served,
and changes in the number of commitments.  By definition,
the offense-specific group average time until first 
release equals the average term imposed for the group
times the group average percent of term served.  Then,
the average number of months until first release for an
entry cohort comprised of several offense groups is equal
to the sum of each offense group's weighted average time
until release; the weight equals an offense-group's share
of total commitments, or 

     TUFR =  T(I)*P(I)*c(I)          (1)

where

     TUFR equals time until first release;


     T(I) equals the average term imposed on the ith offense
group;


     P(I) equals the average percent of term served by the ith
offense group; and


     c(I) is the ith offense group's share of total commitments. 



The identity in equation (1) holds for all time periods. 
Therefore, the change in time until first release equals:



     TUFR(t) - TUFT(t-1)                     (2)



or,



      (Sigma symbol)T (i,t)*P(i,t)*c(i,t) -  

      (Sigma symbol)T(i,t-1)*P(i,t-1)*c(i,t-1)                (3)



This can be rewritten as:



      (Sigma symbol)T(i,t)*P(i,t)*[c(i,t) - c(i,t-1)] +      (4)



      (Sigma symbol)T(i,t)*[P(i,t) - P(i,t-1)]*c(i,t-1) +  (5)



     (Sigma symbol)[T(i,t) - T(i,t-1)]*P(i,t-1)*c(i,t-1)  (6)



where equation (4) represents the amount of the difference in
length of stay due to changes in the offense composition of
prison admissions; equation (5) represents the amount of the
difference due to changes in the percent of term served; and
equation (6) represents the amount of the difference due to
changes in the terms imposed.

*****************************************
Decomposing changes in prison populations 
*****************************************

The change in the prison population between 1986 and 1997 is due
to changes in several factors that affect prison population
growth.  As offenders may arrive in Federal prison by U.S.
district court commitments or by violating conditions of
supervision, the yearend stock prison population consists of two
groups:  those who were committed from U.S. district courts and
those who returned to prison for violating conditions of
supervision.  Similarly, there are two sets of factors affecting
prison population growth:  those related to how district court
committed prisoners arrive, and those related to how supervised
release violators arrive in prison.

Therefore, the number of persons in prison at yearend equals the
number who were committed by district courts and the number who
were committed for reasons of violations, or:

     PP = PP(USDC) + PP(Violators)  (7)

where PP equals the yearend prison population; PP(USDC) equals
the number in prison as a result of a U.S. district court
commitment; and PP(Violators) equals the number in prison
as a result of a violation of conditions of supervision.
Each term on the right-hand side of equation (7)can be 
analyzed separately.

The number of persons in prison at yearend as a result of
district court commitments is defined by the following identity:

     PP(USDC) = M*p*c*s*los(dc)       (8)


where


     PP(USDC) = the number of
          persons in prison at yearend
          who are there by virtue of a 
          U.S. district court commitment;


     M = the number of suspects 
         investigated in criminal matters,
         as measured by the number of
         suspects in criminal matters
         concluded;


     p = P/M or the prosecution rate.
         This is the ratio of the number
         of defendants prosecuted (P) to
         the number of criminal suspects    
         in matters investigated (M).  
         The number of defendants
         prosecuted is measured by the
         number of defendants in cases
         terminated in U.S. district
         court.  The number of suspects
         in matters is as above.



     c = C/P or the conviction rate.  This
         is the ratio of the number of
         defendants convicted in U.S.
         district court (C) to the number
         of defendants prosecuted (P).
         The number prosecuted is
         as above.


     s = S/C or the imprisonment rate.
         This is the ratio of the number 
         of offenders sentenced to prison
         (S) to the number convicted (C). 


     los(dc) = the length of stay for U.S.
         district court committed offend-
         ers.  This is the ratio of the
         number of offenders in prison --
         PP(USDC) -- to the number of
         U.S. district court commitments
         (S) into prison.


Equation (7) is an accounting identity.  For it to hold,
the length of stay is measured as the turnover rate, or the
stock-to-flow ratio.  The turnover rate underestimates the time
until release for entering cohorts when either sentences are
increasing or if the number committed is increasing.  During the
1986-1997 period, both of these occurred; consequently, the
impact of changes in length of stay on prison population growth
will be underestimated.

The number of persons in prison as a result of supervision
violations equals:


     PP(Violators) = R*v*los(v)            (9)


where,


     PP(Violators) = the number in
        prison for violations of

        supervision;


     R = the number under supervision;


     v = V/R or the violation rate.  This is
         the ratio of the number of
         offenders returned to prison for
         reasons of violating conditions
         of supervision (V) to the
         number under supervision (R).


     los(v) = the length of stay for viola-
         tors of supervision.  This also 
         is measured as the ratio of the
         number of supervision violators
         in the prison stock to the
         number of supervision violators
         entering prison during a given
         year.  In the case of supervision
         violators, lengths of stay
         are comparatively short, less
         than 1 year; therefore, the
         magnitude of the bias from this
         turnover rate is negligible.


As was done with the decomposition of changes in length
of stay, the difference in the prison population between
two periods can be related to offense-specific changes in
each individual component in equations (8) and (9). Thus,
the difference in the prison population between two periods
is a weighted sum of the differences in each component,
where the weights equal the offense-specific contribution
to prison commitments.  

     PP(t) - PP(t-1) =


(Sigma symbol)M(i,t)*p(i,t)*c(i,t)*los(dc)(i,t) + 

 

(Sigma symbol)R(i,t)*v(i,t)*l(v)(i,t) -

(Sigma symbol)M(i,t-1)*p(i,t-1)*c(i,t-1)*los(dc)(i,t-1) + 



(Sigma symbol)R(i,t-1)*v(i,t-1)*l(v)(i,t-1)                (10)



where "I" measures the specific offense under consideration. 
Equation (10) can be rewritten as was done with equations (4),
(5), and (6) to yield eight separate equations that measure the
change in the prison population due to changes in:

(a) the number of suspects investigated
(b) the number of defendants prosecuted
(c) the number of defendants convicted
(d) the number of offenders sentenced to prison
(e) the length of stay for U.S. district court committed
prisoners
(f) the number of offenders under supervision
(g) the number of supervised release violators returned to
prison
(h) the length of stay for supervised release violators.


The product of each of these equations is the number of persons
contributed to the prison population by the factor under
consideration.


Estimated number of suspects 
in criminal matters in 1986

The number of suspects in criminal matters concluded during 1986
is used in determining changes in the prison population.  Data
were not directly available on the number of suspects 
in criminal matters concluded during 1986.  The offense-specific
counts of suspects in matters concluded were estimated from data
in two published reports.  The 1986 Compendium of Federal
Justice Statistics gave the offense-specific aggregate counts of
suspects in criminal matters plus appellants in appeals filed
during 1986. The Administrative Office of U.S. Courts (Federal
judiciary) Judicial Business of the U.S. Courts reported counts
of the number of appeals.  



To estimate the number of suspects in criminal matters
concluded, we estimated the number of appellants
subtracted from the aggregate counts of suspects plus
appellants as reported in the compendium. Specifically,
the objective is to estimate the number of appellants included in
the compendium's number of suspects in criminal matters.  Using
compendium aggregate data on defendants in cases filed, plus
appellants, and using Federal judiciary data, an estimator was
developed under the assumption that the ratio of appellants to
defendants plus appellants in the compendium was equal to the
observed ratio of appellants to appellants plus defendants in
the Federal judiciary data.  The number of appellants was
estimated and subtracted from the compendium's number of
suspects plus appellants to yield the number of suspects in
criminal matters concluded. 


Appendix.  Entries to and releases from Federal prison, 1986-97

                       Entries      Proportion
Year      Entries     released*     released*

Total     383108        275950        72.0%
1986       25820         25446        98.6
1987       26684         26152        98.0
1988       24591         23870        97.1
1989       28249         26388        93.4
1990       33124         29664        89.6
1991       32812         28172        85.9
1992       34161         27496        80.5
1993       37065         26698        72.0
1994       34407         22182        64.5
1995       32566         17454        53.6
1996       35254         11038        31.3
1997       38375         11390        29.7


*Represents defendants committed to Federal prison by
U.S. district courts as of December 31, 1997.
Data source:  Federal Bureau of Prisons,  SENTRY data file, annual.


The Bureau of Justice Statistics
is the statistical agency of the
U.S. Department of Justice.
Jan M. Chaiken, Ph.D., is director.

BJS Special Reports address a specific topic
in depth from one or more data sets that cover 
many topics.

William J. Sabol, Senior Research Associate at the Urban
Institute and Project Director of the Federal Justice Statistics
Resource Center, and John McGready, Research Associate at the
Urban Institute, wrote and verified this report.  Gerald Gaes,
Director of Research for the Federal Bureau of Prisons, provided
methodological assistance. John Scalia, Jr., BJS Statistician,
supervised preparation of the report. Tom Hester edited it.
Yvonne Boston and Jayne Robinson prepared the report for final
publication.

June 1999, NCJ 171682



This report, as well as other reports and statistics, can be
found at the Bureau of Justice Statistics World Wide Web site:

http://www.ojp.usdoj.gov/bjs/

Data used in this report and other data that are a part of the
Federal Justice Statistics Resource Center, maintained by the
Urban Institute, can be obtained through the BJS website or at
the following address:

http://fjsrc.urban.org


8/6/99 RCK