United States General Accounting Office

GAO Report to the Subcommittee on Crime,

Committee on the Judiciary, House of

Representatives

November 1996 FEDERAL AND STATE

PRISONS

Inmate Populations,

Costs, and Projection

Models

G O A

years

1921 - 1996

GAO/GGD-97-15

GAO United States

General Accounting Office

Washington, D.C. 20548

General Government Division

B-272244 

November 25, 1996

The Honorable Bill McCollum

Chairman

The Honorable Charles E. Schumer

Ranking Minority Member

Subcommittee on Crime

Committee on the Judiciary

House of Representatives

This report focuses on trends in U.S. prison inmate populations and costs,

and it is intended to assist Congress and the administration in considering

the implications of sentencing policies and law enforcement initiatives.

Our specific objectives in initiating this review were to identify (1) the

trends in federal and state prison inmate populations and operating and

capital costs since 1980, including projections for 2000 and beyond and the

reasons for the trends and (2) the models and methodologies used by

federal and state corrections agencies and nongovernmental forecasting

organizations to make these projections, including whether any validity or

reliability assessments have been conducted. Although you did not request

this review, we addressed this report to you, as agreed, because of your

interest in prison issues, as exemplified by the hearings you held on

June 8, 1995.

To accomplish our objectives, we obtained and reviewed relevant

population, cost, and modeling information from the Federal Bureau of

Prisons (BOP), the National Council on Crime and Delinquency (NCCD), and

corrections agencies in the two states with the largest numbers of inmates

(California and Texas). Also, we relied extensively on data compiled by

the federal Bureau of Justice Statistics (BJS) and the U.S. Bureau of the

Census, and data in private publications, such as the Corrections

Compendium, which is a journal published by CEGA Publishing in Lincoln,

NE. We did not independently verify the accuracy of the prison inmate

population and cost data. Our objectives, scope, and methodology are

discussed in more detail in appendix I.

We performed our work from May 1996 to September 1996 in accordance

with generally accepted government auditing standards.

Results in Brief From 1980 to 1995, the latest year for which complete data were available,

the total federal and state1

 prison population grew at an average annual

1

State data include all 50 states and the District of Columbia.

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B-272244 

rate of 8.5 percent. As figure 1 shows, the total prison population grew

from about 329,800 inmates in 1980 to about 1.1 million inmates in 1995,

which is an increase of about 242 percent. During this period, the federal

inmate population grew about 311 percent, and the inmate populations

under the jurisdiction of state prisons grew about 237 percent. The

corresponding average annual growth rates were 9.9 percent for federal

populations and 8.4 percent for state populations.

Figure 1: Trends in Prison Inmate Populations, 1980 Through 1995

Number of inmates in thousands

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995

Calendar year

Total (federal and state)

All states

Federal

Source: BJS.

Federal and state corrections agencies—as well as nongovernmental

forecasting organizations, such as NCCD—have projected that the prison

population will continue to grow in future years. For example, in

June 1996, BOP projected that the federal prison population could reach

about 125,000 inmates by 2000, an increase of 25 percent over the 1995

Page 2 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

level. In July 1995, NCCD projected that the total federal and state prison

population under sentencing policies in effect in 1994 could reach

1.4 million inmates by 2000, representing an increase of about 24 percent

over the 1995 level.

The size of the prison population is a function of many factors, including

the nation’s crime levels, sentencing laws, and law enforcement policies.

In recent years, inmate population growth can be traced in large part to

major legislative initiatives that are intended to get tough on crime,

particularly on drug offenders. Examples of this new get-tough policy

include mandatory minimum sentences and repeat offender provisions.

Reflecting the growth in inmate populations, U.S. prison (federal and

state) annual operating costs grew from about $3.1 billion in fiscal year

1980 to about $17.7 billion in current dollars in fiscal year 1994. All prison

costs (operating and capital costs) cumulatively totaled about $163 billion2

during the fiscal years 1980 to 1994 period. The corresponding average

annual growth rate for this period was 9.1 percent in inflation-adjusted

terms. In June 1996, BOP projected that its prison operating costs could

total about $3.6 billion in fiscal year 2000, which is an increase of about 88

percent over the fiscal year 1994 level. BOP also projected that its capital

costs for new federal prisons scheduled to begin operations during fiscal

years 1996 to 2006 could total about $4 billion. Regarding the states’ needs,

NCCD has estimated that $10.6 billion to $15.1 billion could be needed to

construct additional prisons to accommodate anticipated inmate

population increases from 1995 to 2000 and that $21.9 billion could be

needed by the end of the decade to operate these prisons.

To forecast prison inmate populations, BOP, NCCD, California, and Texas

each use a form of microsimulation modeling. Microsimulation provides

the flexibility to adjust assumptions and data in response to new

sentencing laws or policies and other criminal justice or law enforcement

initiatives that could affect the size of prison populations.3

 Except for BOP’s

projection model, on the basis of a literature search and discussions with

federal and state agency officials, we did not identify any independent

assessments of the various projection models’ validity or reliability.

Generally, officials commented that projections beyond 5 years, and

perhaps even beyond 2 years, are usually considered rough estimates.

2

See tables III.1, III.2, and III.3 in appendix III.

3

The various agencies or organizations do not use modeling to project operating and capital costs.

Rather, costs generally are projected linearly using historical cost data (e.g., per-inmate operating

costs and per-bed construction costs) adjusted for inflation and projected population data.

Page 3 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

However, BOP and NCCD have tracked the accuracy of their respective

projections. According to BOP, its projections of federal prison inmate

populations for 1991 to 1995 were within 1.4 percent (on average) of the

actual populations. Also, according to NCCD, its projections for 1991

through 1994 were within 2 percent (on average) of the actual populations.

Background In recent years, Gallup opinion polls have indicated that the American

public is concerned about crime and related violence. For example, in a

1995 poll, 27 percent of the respondents listed crime and violence as the

most important problems facing the country. Polls also have suggested

that tougher anticrime legislation is a top priority for the public. For

instance, 80 percent of the respondents to a 1996 Gallup Poll supported

life sentences for drug dealers. Congress has authorized grants to the

states that support tougher sentencing policies for criminals and expanded

prison construction to house the growing number of inmates. For

example, in the Department of Justice’s 1996 appropriations,4

 Congress

authorized about $10.3 billion in grants to states for fiscal years 1996

through 2000 for, among other things, building or expanding correctional

facilities to house persons convicted of violent crimes.

According to BJS’ National Crime Victimization Survey (April 1996),5

 there

were 51 violent victimizations6

 per 1,000 U.S. residents in 1994, which was

the latest year that complete data were available. Since its inception in

1973, the survey has determined that crime rates and levels have

fluctuated over extended periods. Specifically, violent crime rates leveled

off between 1992 and 1994, compared with a 20-percent decline between

1981 and 1986 and a 15-percent rise between 1986 and 1991. Property

crime7

 continued a general 15-year decline. The survey did not provide any

reasons for the fluctuations in crime rates and levels. Even though crime

rates have fluctuated, overall crime rates in the 1990s remain substantially

higher than those in the 1960s. For example, according to Uniform Crime

Reports data compiled by the Federal Bureau of Investigation, the nation’s

4

Public Law 104-134, April 26, 1996.

5

Conducted in 1994, the survey measured personal and household offenses, including crimes not

reported to police, by interviewing all occupants age 12 or older in a nationally representative sample

of U.S. households, including persons living in group quarters, such as dormitories. In total,

approximately 120,000 residents in 56,000 housing units were interviewed about the crimes they had

experienced in the previous 6 months.

6

Violent crimes included rape/sexual assault, robbery, aggravated and simple assault as measured by

the survey, and murder as reported to the Federal Bureau of Investigation.

7

The survey defined property crimes as household burglary, motor vehicle theft, and thefts of other

property.

Page 4 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

overall crime rate was about 2,000 crimes per 100,000 residents in the early

1960s compared with 5,374 crimes per 100,000 residents in 1994.

Against the backdrop of these higher crime rates, there is a continuing

debate over the use of incarceration as a means of addressing increasing

crime. Both proponents and opponents of increasing the use of

incarceration as a solution to the crime problem can cite research to

support their positions. For example, proponents of increased

incarceration assert that investing in new prisons will have long-term

benefits of crime reduction.8

 On the other hand, critics of increased

incarceration argue that continued prison-building is wasteful and

unaffordable and is unlikely to affect crime rates.9

In 1994, RAND issued a study of California’s “three strikes” law, which

mandates sentences ranging from 25 years to life for certain three-time

felony offenders.10 The study, which weighed crime reduction and cost,

concluded that the California law, if fully implemented, will reduce serious

felonies committed by adults in the state by between 22 and 34 percent

below what may have occurred. The study also concluded that the

reduction in crime would be achieved at an additional cost of between

$4.5 billion and $6.5 billion in current dollars annually. According to the

study, most of the cost increase would result from the need to build and

operate additional prisons to house the inmate population, which could be

expected to double as a result of sentencing under the law. A more recent

RAND study11 indicates that some preventative measures, such as parent

training and graduation incentives, could potentially reduce crime rates

more cost effectively than incarceration.

8

John J. DiIulio, Jr., “Prisons Are A Bargain, by Any Measure,” The Wall Street Journal, January 16,

1996. Mr. DiIulio, a professor of politics and public affairs at Princeton University, also is one of the

authors of The State of Violent Crime in America (Council on Crime in America: Washington, D.C.),

January 1996.

9

For example, see the testimony of Todd R. Clear presented in hearings on the “Federal Prison

Population: Present and Future Trends” before the House Subcommittee on Intellectual Property and

Judicial Administration, Committee on the Judiciary, 103d Cong., 1st Sess. 80-98 (1993).

10Peter W. Greenwood, et al, RAND, Three Strikes and You’re Out: Estimated Benefits and Costs of

California’s New Mandatory Sentencing Law (RAND/MR-509-RC), 1994.

11Peter W. Greenwood, et al, RAND, Diverting Children from a Life of Crime: What Are the Costs and

Benefits? (RAND/MR-699-UCB/RC/IF), 1996.

Page 5 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

Trends in Federal and

State Prison Inmate

Populations and Costs

Federal and state prison inmate populations have been growing since

1980, reaching about 1.1 million inmates in 1995. Federal and state

corrections agencies and nongovernmental forecasting organizations

project that these populations will continue to grow, potentially reaching

1.4 million inmates in 2000. Prison operating and capital costs12 have also

been growing and are projected to continue doing so in the future. For

federal and state prisons, operating and capital costs cumulatively totaled

about $163 billion13 for fiscal years 1980 through 1994.

Prison Inmate Populations

(1980 Through 1995)

From 1980 to 1995, which was the latest year that complete data were

available, the total U.S. prison inmate population under federal and state

jurisdiction14 grew by about 242 percent, from 329,821 to 1,127,132,15

respectively. The corresponding average annual prison population growth

rate during this period was 8.5 percent (9.9 percent for the federal

population and 8.4 percent for the state populations). The prison

population increased at a slower rate—6.8 percent—between 1994 and

1995 than the average growth rate. Although an August 1996 BJS report16 on

prison and jail inmates—the source for our prison inmate population

data—did not provide specific reasons for the decrease in the rate of

growth, a BJS official commented that the smaller growth rate may be the

result of the growing population base, currently over 1 million inmates.

Nevertheless, we do not know whether this marks the start of a trend

toward smaller rates of growth.

As previously shown in figure 1, the federal prison inmate population grew

from 24,363 in 1980 to 100,250 in 1995, which is an increase of about

312 percent. The state prison population grew from 305,458 inmates in

1980 to 1,026,882 inmates in 1995, which is an increase of about

12As defined by the Census Bureau—our source for cost data—“costs,” or “direct expenditures,” are

payments to employees, suppliers, contractors, beneficiaries, and other final recipients of government

payments. Expenditures are net of recoveries and other correcting transactions and exclude

retirement of debt, investment in securities, extensions of credit, and agency transactions.

13See table III.3 in appendix III.

14According to BJS, this population includes inmates serving sentences of more than 1 year

(“sentenced prisoners”); those with sentences of a year or less; and those with no sentences (e.g.,

those awaiting trial in states with combined jail/prison systems). These inmates are under the

jurisdiction of correctional authorities in the 50 states, the District of Columbia, and the federal

government. Inmates under jurisdiction include persons under the legal authority of a prison system

held elsewhere or outside its facilities.

15According to BJS, this is an advance count of prisoners under federal and state jurisdiction for 1995,

and it may be revised.

16BJS, Prison and Jail Inmates, 1995 (NCJ-161132), August 1996.

Page 6 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

236 percent. In California, the state prison inmate population grew from

24,569 in 1980 to 135,646 in 1995, which is an increase of about

452 percent. In Texas, the inmate population grew from 29,892 in 1980 to

127,766 in 1995, which is an increase of about 327 percent. Not all states

exhibited inmate population increases to such an extent. For example, in

Maine, the inmate population grew from 814 in 1980 to 1,447 in 1995,

which is an increase of about 78 percent. In North Carolina, the inmate

population grew from 15,513 in 1980 to 29,374 in 1995, which is an increase

of about 89 percent.

Inmate Incarceration Rates

(1980 Through 1995)

Corresponding to the growth in prison populations, the incarceration

rates17 for federal and state prison inmates have also shown steady growth

during the 16-year period of 1980 through 1995. As figure 2 shows, the total

incarceration rate grew from 145 inmates in 1980 to 428 inmates in 1995

for every 100,000 U.S. residents, which is an increase of about 195 percent.

Reflecting an even larger percentage increase (about 245 percent), the

incarceration rate for federal inmates grew from 11 inmates for every

100,000 residents in 1980 to 38 inmates for every 100,000 residents in 1995.

Because most prisoners are under state jurisdiction, the incarceration rate

for state inmates closely follows (and, indeed, is largely determinative of)

the nation’s total incarceration rate. Specifically, the incarceration rate for

states grew from 134 inmates for every 100,000 residents in 1980 to 390

inmates for every 100,000 residents in 1995, which is an increase of about

191 percent. During this period, the incarceration rate in California

increased 312 percent, growing from 104 inmates for every 100,000

residents in 1980 to 428 inmates for every 100,000 residents in 1995. The

incarceration rate in Texas increased 222 percent, growing from 210

inmates to 677 inmates for every 100,000 residents in 1980 and 1995,

respectively.

17The rate of incarceration is the total number of prisoners in correctional facilities per 100,000 U.S.

resident population.

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Figure 2: Trends in Incarceration Rates, 1980 Through 1995

Inmates per 100,000 U.S. residents

0

50

100

150

200

250

300

350

400

450

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995

Calendar year

Total (federal and state)

All states

Federal

Source: BJS.

Reasons for Prison

Population Growth

According to various sources, including BJS and the U.S. Sentencing

Commission, the significant growth in federal and state inmate

populations since the 1980s is largely the result of changes in criminal

behavior, law enforcement practices, sentencing law and policy, and

release practices. For example, according to BJS, during the 1980s, an

increasing number of probation and parole violators returned to prison,

while in the 1990s, declining rates of release have sustained the growth in

inmate populations.

More specifically, regarding federal offenders, under the Sentencing

Reform Act of 1984,18 parole was abolished, and good-time credits (time

off sentence for good behavior) were limited to 54 days per year. In 1986,

18Public Law 98-473, October 12, 1993.

Page 8 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

the Anti-Drug Abuse Act19 established mandatory minimum sentences for

certain drug offenses. In 1988 and 1990, Congress passed additional

sentencing legislation, which increased mandatory minimum sentences for

drug and weapons offenses. As a result of these statutory changes, the use

of probation has been reduced and the length of prison stays has

increased. According to BJS data, after 1986, the average time served in

federal prisons increased from 15 months to 24 months. For violent

offenses, the time served increased from 50 months to 56 months, and the

time served for drug offenses increased from 22 months to 33 months.20

Particularly noteworthy has been the trend regarding drug offenders as a

percentage of the total inmate population. According to a 1991 study by

the U.S. Sentencing Commission, drug offenders constituted about

91 percent of all federal defendants sentenced under mandatory minimum

provisions.21 According to BJS, in 1993, which was the latest year that

complete data were available, drug offenders constituted 26 percent of all

federal and state inmates,22 whereas these offenders constituted 8 percent

of all inmates in 1980. Also, BJS has reported that the increase in drug

offenders accounts for nearly three-fourths of the total growth in federal

prison inmates since 1980.

The state prison inmate populations have grown as a result of, among

other things, the increased number of arrests, higher probabilities of

incarceration, and more severe sanctions. Specifically, according to BJS,

the number of arrests increased by 41 percent between 1980 and 1993, the

latest year that complete data were available. The rate of sending

offenders to prison also increased. For example, the likelihood of

incarceration increased 5-fold for drug violations and 4-fold for weapons

offenses. According to the California Department of Corrections,23 the

prison population in that state has grown because of court decisions, voter

initiatives, and legislation, all of which have resulted in stronger law

enforcement and more severe criminal sanctions. For example, a

California law prohibits the use of good-time allowances to reduce the

sentences of repeat offenders convicted of certain violent felonies. State

19Public Law 99-570, October 27, 1986.

20BJS, Prisoners in 1994 (NCJ-151654), August 1995.

21U.S. Sentencing Commission, Special Report to Congress: Mandatory Minimum Penalties in the

Federal Criminal Justice System, August 1991.

22In 1993, drug offenders constituted 60 percent of all federal inmates and 22 percent of all state

inmates.

23The California Department of Corrections is responsible for, among other things, the incarceration of

adult felons and nonfelon narcotics addicts. The Department also supervises and treats parolees

released to the community.

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B-272244 

corrections officials expected that the law may result in inmates’ serving

additional time, which could lead to an increase in the state’s prison

population in future years.

Prison Population

Projections for 2000

While sources differed somewhat in their projected growth for federal and

state prison inmate populations, they all showed substantial anticipated

increases for these populations in 2000 and beyond. In June 1996, BOP

projected that the federal prison population could reach about 125,000

inmates by 2000, which is a 25-percent increase over the 1995 level (see

table 1). In July 1995, NCCD projected that, under sentencing policies in

effect in 1994, the total inmate population for federal and state prisons

could reach 1.4 million by 2000, which is an increase of 24 percent over the

1995 level. NCCD also projected that, if all states were to adopt

truth-in-sentencing statutes, which would require inmates to serve at least

85 percent of their sentences, the states’ prison population could grow by

an additional 190,000 inmates and total about 1.6 million inmates by 2000,

which would be an increase of about 42 percent over the 1995 level.

Table 1: Projected Prison Populations

in 2000

Prison system Source of projection

Total projected

population in

2000

Percentage

increase from

1995 to 2000

Federal BOP 125,144 25

Federal and states NCCD 1,400,000 24

Federal and states Corrections

Compendium (April 1996) 1,341,832 19

California California Department of

Corrections 203,593 50

Texas Texas Criminal

Justice Policy Council 143,748 13

Sources: As indicated in table.

The April 1996 issue of the Corrections Compendium presented a

compilation of inmate population projections that were based on a survey

of federal and state corrections agencies. The combined self-reported

projections showed that the federal and state prison population could

reach over 1.3 million in 2000, representing an increase of 19 percent over

the 1995 level. However, the survey summary in the Compendium

indicated that this total may be understated. According to the summary, if

the historical growth rate (8.7 percent per year from 1980 through

1994) continues in future years, the prison population could actually

Page 10 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

increase by 95 percent over the 1994 level, essentially doubling to about

2 million inmates by 2002.

In July 1995, NCCD projected that the inmate population in California could

reach about 210,000 by 2000, which would be an increase of 55 percent

over the 1995 level. Separately, in spring 1996, the California Department

of Corrections projected that the state’s prison population could reach

203,593 inmates in 2000, which would be an increase of about 50 percent

over the 1995 level. For Texas, in July 1995, NCCD projected that the inmate

population could reach about 149,000 by 2000, which would be an increase

of about 17 percent over the 1995 level. In September 1996, the Texas

Criminal Justice Policy Council projected that the state’s prison

population could reach 143,748 in 2000, which would be an increase of

about 13 percent over the 1995 level.24

Appendix II presents additional information about actual and projected

federal and state prison inmate populations and incarceration rates.

Prison Operating Costs

(Fiscal Years 1980 Through

1994)

Prison operating costs25 grew steadily during fiscal years 1980 to 1994,

reflecting in part the growth in prison populations. As figure 3 shows, total

U.S. prison operating costs grew from about $3.1 billion in fiscal year 1980

to about $17.7 billion in current dollars in fiscal year 1994. This is an

increase of 224 percent based on constant or inflation-adjusted dollars.26

Of this total, federal prison operating costs grew from about $319 million

in fiscal year 1980 to about $1.9 billion in fiscal year 1994, which is an

increase of about 242 percent based on constant dollars. The

corresponding average annual growth rate during this period was 9.9

percent. State prison operating costs grew from about $2.8 billion in fiscal

year 1980 to $15.8 billion in fiscal year 1994, which is an increase of 222

percent based on constant dollars. The corresponding average annual

24According to the Council’s September 1996 correctional population projection report, this projection

was revised downward from earlier versions to account for the reduced growth in Texas’ correctional

population. According to the report, the reduced growth has resulted from a decline in reported crime,

a stabilization in the number of new convictions, a decline in parole revocations, and a decline in the

number of offenders sentenced to prison.

25As defined by the Census Bureau, prison operating costs include compensation of officers and

employees, supplies, materials, operating leases, and contractual services. Operating costs also include

repairs to existing works and structures.

26In this report, except for projections or future trends, percentage increases involving costs are based

upon the conversion of current dollars to constant or inflation-adjusted dollars. Specifically, in

calculating percentage increases for operating and capital costs during past years, we used annual

implicit price deflators (as published in the U.S. Department of Commerce’s Survey of Current

Business) to adjust all dollars to 1994 purchasing power.

Page 11 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
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growth rate during this period was 8.7 percent. In California, operating

costs grew from about $320 million in fiscal year 1980 to $2.6 billion in

fiscal year 1994, which is an increase of 357 percent based on constant

dollars. In Texas, operating costs grew from about $105 million in fiscal

year 1980 to $1.2 billion in fiscal year 1994, which is an increase of

529 percent based on constant dollars.

Figure 3: Trends in Prison Operating Costs, Fiscal Years 1980 Through 1994

Current dollars in billions

0

2

4

6

8

10

12

14

16

18

20

22

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

Federal

All states

Note: Dollar figures represent actual dollars (no adjustment for inflation).

Source: Table III.1 in appendix III.

Prison Capital Costs

(Fiscal Years 1980 Through

1994)

Prison capital costs,27 while growing overall, have actually fluctuated on

almost a year-to-year basis during fiscal years 1980 to 1994. As figure 4

shows, total U.S. prison capital costs grew from about $538 million in

27As defined by the Census Bureau, prison capital costs are the direct expenditures for contract or

forced account construction of buildings, roads, and other improvements, purchase of equipment,

land, and existing structures, and payment of capital leases. Capital costs also include expenditures for

additions, replacements, and major alterations to fixed works and structures, but exclude repairs to

such works and structures. Repairs are treated as operating expenditures.

Page 12 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

fiscal year 1980 to about $2.3 billion in current dollars in fiscal year 1994.

This is an increase of 141 percent based on constant or inflation-adjusted

dollars. Federal prison capital costs grew from about $22 million in fiscal

year 1980 to about $312 million in fiscal year 1994, representing an

increase of about 715 percent (based on constant dollars). The

corresponding average annual growth rate during this period was 87.9

percent.28 State prison capital costs grew from about $516 million in fiscal

year 1980 to about $2 billion in fiscal year 1994, representing an increase

of about 116 percent based on constant dollars. The corresponding

average annual growth rate during this period was 7.4 percent. In

California, capital costs grew from $16 million in fiscal year 1980 to

$413 million in fiscal year 1994, which is an increase of 1,327 percent

based on constant dollars. In Texas, capital costs grew from $20 million in

fiscal year 1980 to about $577 million in fiscal year 1994, which is an

increase of 1,531 percent based on constant dollars.

28The average annual growth rate is distorted by large increases in certain fiscal years. For example, in

fiscal year 1983, federal capital costs increased by almost 700 percent over the level in fiscal year 1982.

Also, in fiscal year 1990, capital costs increased by about 440 percent over the level in fiscal year 1989.

Page 13 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
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Figure 4: Trends in Prison Capital Costs, Fiscal Years 1980 Through 1994

Current dollars in billions

0

1

2

3

4

5

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

Federal

All states

Note: Dollar figures represent actual dollars (no adjustment for inflation).

Source: Table III.2 in appendix III.

Projections of Prison

Operating and Capital

Costs

BOP estimates federal prison operating costs to grow through fiscal 2000,

while capital costs are expected to fluctuate on a year-by-year basis.

Specifically, in June 1996, BOP projected that its operating costs could

grow to about $3.6 billion by fiscal year 2000, almost double the level in

fiscal year 1994. BOP also projected that its capital costs for new federal

prisons scheduled to begin operations during fiscal years 1996 to 2006

could total about $4 billion. According to Justice officials, these cost

increases were projected on the basis of historically high rates of prison

population increases. According to these officials, since recent BJS

statistics show that the rate of increase in prison populations from 1994 to

1995 was below the average for the preceding 5 years, the BOP cost

projections for 2000 and beyond may be overestimated.

NCCD has estimated that state prison population increases from 1995 to

2000 could result in total additional capital and operating costs of

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B-272244 

$32.5 billion to $37 billion for this period. Specifically, NCCD estimated that

$10.6 billion to $15.1 billion could be needed to construct additional state

prisons, and that $21.9 billion could be needed by the end of the decade to

operate these prisons.

Appendix III presents additional information about actual and projected

federal and state operating and capital costs.

Models and

Methodologies Used

to Project Prison

Populations

BOP, NCCD, California, and Texas each use microsimulation models to

project prison inmate populations.29 The models are similar in providing

flexibility to adjust assumptions and data in response to new sentencing

laws or policies and other criminal justice or law enforcement initiatives

that could affect the size of prison populations in the respective

jurisdiction. Appendix IV provides more detailed information about

microsimulation and other models and methodologies used to project

inmate populations.

On the basis of a literature search and discussions with federal and state

agency officials, we did not identify any independent assessments of the

various projection models’ validity or reliability, except for BOP’s model.

This model, according to BOP officials, has been subjected to various

reviews. For example, the officials made the following comments:

• In 1993, BOP staff published a paper (which was peer reviewed) on the

projection methodology.30

• Justice’s budget staff annually reviews BOP’s inmate population projections

and often reports to the Attorney General on the accuracy of the

projections.

Some of the forecasting organizations and state corrections agencies have

tracked and self-reported on the accuracy of their respective projections.

For example, according to BOP, its projections of federal prison inmate

populations for 1991 to 1995 were within 1.4 percent (on average) of the

actual populations. Also, according to NCCD, its projections for 1991

through 1994 were within 2 percent (on average) of the actual populations.

29As previously noted, the various agencies or organizations do not use modeling to project operating

and capital costs. Rather, costs generally are projected linearly using historical cost data adjusted for

inflation and projected population data. For example, to project its operating costs, BOP adjusts actual

per-inmate costs by an annual inflation factor of 3.1 percent.

30Gaes, G.G., Simon, E.S., and Rhodes, W.M., “20/20 Hindsight: Effectiveness of Simulating the Impact

of Federal Sentencing Legislation on the Future Prison Population,” The Prison Journal, 1993, pp. 5-29.

Page 15 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

However, BOP officials and a modeling expert said that assessing a model’s

reliability by comparing projections with actual populations is not

necessarily the only approach. For instance, the officials noted that after

projections showing potential impacts are presented or published,

legislators or administrators are more likely to modify or change certain

policies or practices, taking the projections into consideration. Thus,

according to these officials, another benefit of a population simulation is

to inform the public policy debate.

The April 1996 issue of the Corrections Compendium presented the results

of a survey that asked respondents to report on the accuracy of their

models’ population projections. The survey was originally sent to federal

and state corrections agencies in October 1995, and the responses with the

applicable data were collected through February 1996. Of the 39

respondents31 to this question, 54 percent reported that their past

projections were “accurate,”32 23 percent reported that their past

projections were “too low,” and 8 percent said their past projections were

“too high.”33 The other respondents to the overall survey reported that they

either did not project populations or did not assess the accuracy of their

projections.

Agency Comments

and Our Evaluation

We obtained comments on the draft of this report from Justice officials,

including the Director of Justice’s Audit Liaison Office, BOP’s Chiefs of

Research and Evaluation and Budget Development, and BJS’ Chief of

Corrections Statistics. These officials generally agreed with the contents of

the draft report. However, BOP and BJS officials provided technical

comments and clarifications related to certain numerical data in the

report. Also, the BOP officials provided revised federal prison inmate data.

We have incorporated these technical comments, clarifications, and

revisions where appropriate in this report.

Regarding prison costs, BJS officials expressed the view that actual

expenditure data compiled and published by the Census Bureau (e.g.,

Census of Government Finances) would be more accurate and complete

than data from The Corrections Yearbook, the source we used for the draft

of this report. Accordingly, from the Census Bureau, we obtained state

prison expenditure data for fiscal years 1980 through 1994 (the latest year

31The respondents were BOP, 37 states, and the District of Columbia.

32For example, BOP, California, and Texas reported that their projections were accurate.

33The survey did not define or specify a given time period for “past” projections.

Page 16 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
B-272244 

that complete data were available), and we incorporated this information

and revised the related analyses in this report where appropriate.

In our draft report, we noted that we did not identify any independent

assessments regarding the validity or reliability of the various models used

to project federal and state prison inmate populations. However, in

commenting on the draft report, BOP officials called to our attention

examples of various reviews or evaluations that could be considered

assessments of the Bureau’s microsimulation model. We incorporated

BOP’s comments and examples in this report.

We also obtained comments on the draft of this report from NCCD’s

Executive Vice President and a NCCD Senior Researcher. These officials

agreed with the contents of this report and stated that it factually

represented information and statistical data developed by and previously

published by NCCD. The officials also offered one technical clarification,

which we have incorporated in this report.

We are providing copies of this report to the Attorney General; the

Assistant Attorney General, the Office of Justice Programs; the Director,

BOP; and other interested parties. Copies also will be made available to

others upon request. The major contributors to this report are listed in

appendix V. Please contact me on (202) 512-8777 if you or your staff have

any questions.

Laurie E. Ekstrand

Associate Director, Administration

 of Justice Issues

Page 17 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Contents

Letter 1

Appendix I 

Objectives, Scope,

and Methodology

20

Appendix II 

Trends in Federal and

State Prison Inmate

Populations and

Incarceration Rates

23

Prison Inmate Populations and Incarceration Rates (1980

Through 1994)

23

Projected Prison Inmate Populations 25

Growth in Other Adult Correctional Populations 27

Appendix III 

Trends in Federal and

State Prison

Operating and Capital

Costs

30

Prison Operating Costs (Fiscal Years 1980 Through 1994) 30

Prison Capital Costs (Fiscal Years 1980 Through 1994) 30

Projected Federal Prison Operating and Capital Costs 32

Appendix IV 

Models and

Methodologies Used

for Projecting Prison

Inmate Populations

33

Microsimulation Modeling Is Most Widely Used 33

Reliability of Microsimulation Models 36

Other Models and Methods 36

Appendix V 

Major Contributors to

This Report

38

General Government Division, Washington, D.C. 38

Office of the General Counsel, Washington, D.C. 38

Dallas Field Office 38

Tables Table 1: Projected Prison Populations in 2000 10

Table II.1: Federal Prison Inmate Populations and Incarceration

Rates at Year-End, 1980 Through 1995

23

Table II.2: Federal Prison Inmate Populations at Fiscal Year-End,

1980 Through 1995

24

Page 18 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Contents

Table II.3: State Prison Inmate Populations and Incarceration

Rates at Year-End, 1980 Through 1995

25

Table II.4: Projected Federal Prison Inmate Populations, 1996

Through 2006

26

Table II.5: Projected Prison Inmate Populations for 23 States,

1996 Through 2000

27

Table II.6: Adult Correctional Populations by Category, 1980 and

1995

28

Table III.1: Federal and State Prison Operating Costs in Current

Dollars, Fiscal Years 1980 Through 1994

30

Table III.2: Federal and State Prison Capital Costs in Current

Dollars, Fiscal Years 1980 Through 1994

31

Table III.3: Federal and State Prison Total Cumulative Costs in

Current Dollars, Fiscal Years 1980 Through 1994

31

Table III.4: Projected Federal Prison Operating and Capital Costs,

Fiscal Years 1996 Through 2006

32

Table IV.1: Types of Models Used by BOP and States to Project

Prison Populations

34

Figures Figure 1: Trends in Prison Inmate Populations, 1980 Through

1995

2

Figure 2: Trends in Incarceration Rates, 1980 Through 1995 8

Figure 3: Trends in Prison Operating Costs, Fiscal Years 1980

Through 1994

12

Figure 4: Trends in Prison Capital Costs, Fiscal Years 1980

Through 1994

14

Figure II.1: Distribution of Adult Correctional Populations, 1980

and 1995

29

Abbreviations

BJS Bureau of Justice Statistics

BOP Bureau of Prisons

FEDSIM Federal Sentencing Simulation model

NCCD National Council on Crime and Delinquency

Page 19 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix I 

Objectives, Scope, and Methodology

We initiated this review to identify (1) the trends in federal and state

prison inmate populations and operating and capital costs since 1980,

including projections for 2000 and beyond and the reasons for these trends1

and (2) the models and methodologies used by federal and state2

corrections agencies and nongovernmental forecasting organizations to

make these projections, including whether any validity or reliability

assessments had been done.

To address these objectives, we initially conducted a literature search to

identify available data sources and to determine to what extent these

issues had received congressional attention. In the latter regard, we noted

that a Subcommittee of the House Committee on the Judiciary held

hearings in 19933

 that were useful in our analyses.

More specifically, to identify the trends in prison populations and costs,

we contacted relevant federal agencies, such as the Bureau of Justice

Statistics (BJS), the Federal Bureau of Prisons (BOP), and the U.S. Bureau of

the Census, and corrections agencies in the two states with the largest

prison populations (California and Texas). BJS compiles and publishes

considerable statistical information covering both federal and state

correctional systems. For example, two relevant series of BJS publications

are the Sourcebook of Criminal Justice Statistics and Correctional

Populations in the United States. The Census Bureau compiles and

publishes, among other things, statistical information about federal and

state government expenditures. For example, relevant series of Census

Bureau publications are the Census of Government Finances and State

Government Finances.

From BOP, we obtained historical as well as projected data covering both

populations and costs for federal prisons. From the state agencies, we

obtained and reviewed historical and projected prison inmate population

data. State agency officials told us that prison operating and capital costs

generally are not projected beyond the next fiscal year.

1

We have previously reported on issues related to prison expansion and crowding. See Federal Prison

Expansion: Overcrowding Reduced but Inmate Population Growth May Raise Issue Again

(GAO/GGD-94-48, Dec. 14, 1993) and Prison Crowding: Issues Facing the Nation’s Prison Systems

(GAO/GGD-90-1BR, Nov. 2, 1989).

2

State data include all 50 states and the District of Columbia.

3

“Federal Prison Population: Present and Future Trends,” hearings before the House Subcommittee on

Intellectual Property and Judicial Administration, Committee on the Judiciary, 103d Cong., 1st Sess.

80-98 (1993).

Page 20 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix I 

Objectives, Scope, and Methodology

Furthermore, in identifying prison population and cost trends, we also

contacted nongovernmental sources, such as the National Council on

Crime and Delinquency (NCCD). As a private organization engaged in

research, training, and advocacy programs to reduce crime and

delinquency, NCCD has published several studies of prison-related topics,

including projections of inmate populations.4

 Also, another useful

nongovernmental source was the Corrections Compendium, which is a

journal from CEGA Publishing.

We discussed the population and cost data we obtained with cognizant

officials at the federal and state agencies and the nongovernmental

organizations. We did not independently verify the accuracy and quality of

the data we obtained.

To identify the models and methodologies used by federal and state

corrections agencies and nongovernmental organizations to make

projections, we obtained and reviewed modeling and methodology

information from BOP, NCCD, the Corrections Compendium, the California

Department of Corrections, and the Texas Criminal Justice Policy Council.5

We focused our review on BOP’s Federal Sentencing Simulation model,

NCCD’s Prophet model (used by 23 states in addition to NCCD), and Texas’

JUSTICE model (Texas has the second largest prison inmate population).

To identify the extent, if any, to which the forecasting models and

methodologies had been assessed for validity and reliability, we conducted

a literature search.6

 Also, we interviewed officials in BOP’s Office of

Research and Evaluation, which is responsible for, among other things,

forecasting federal inmate populations. Similarly, we interviewed state

corrections agency officials in California and Texas. We discussed issues

related to the models and methodologies and their validity and reliability

with cognizant officials from BOP and NCCD and the author of a 1990

4

For example, see Michael A. Jones and James Austin, “The NCCD National Prison Population

Forecast: The Cost of Truth-in-Sentencing Laws,” NCCD Focus (San Francisco, CA: National Council

on Crime and Delinquency), July 1995.

5

The Council was created as an independent state agency in 1983 by the Texas legislature. As

mandated by state law, the Council’s basic operational activity includes making projections and impact

simulations regarding criminal justice policy alternatives.

6

For example, the April 1996 issue of Corrections Compendium presents the results of a survey on

inmate population projections. The survey asked respondents whether past projections had been

accurate.

Page 21 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix I 

Objectives, Scope, and Methodology

BJS-sponsored study that reviewed (but did not evaluate) some of the

projection models used by federal and state criminal justice systems.7

7

BJS, Models of the Criminal Justice System: A Review of Existing Impact Models (NCJ-124011),

prepared by William Rhodes, Abt Associates, Inc. (Cambridge, MA), June 1990.

Page 22 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

Federal and state prison inmate populations—and corresponding

incarceration rates—have been growing since 1980. Federal and state

corrections agencies and nongovernmental forecasting organizations

project that these populations will continue to grow through 2000 and

beyond. Populations in the other three correctional categories—probation,

parole, and jail—have also grown since 1980.1

 However, in terms of the

percentages of the overall adult correctional population, the relative

distribution of adult offenders among the four categories were similar in

1994 and 1980.

Prison Inmate

Populations and

Incarceration Rates

(1980 Through 1994)

Table II.1 shows that the federal prison inmate population and the

corresponding incarceration rate have grown consistently from 1980 to

1995. By 1995, the prison population had grown 4-fold from the 1980 level,

reaching over 100,000 inmates. The incarceration rate had grown more

than 3-fold, reaching 38 inmates for every 100,000 U.S. residents in 1995.

Table II.1: Federal Prison Inmate

Populations and Incarceration Rates at

Year-End, 1980 Through 1995 Calendar year Population

Inmates per 100,000

U.S. residents

1980 24,363 11

1981 28,133 12

1982 29,673 13

1983 31,926 14

1984 34,263 14

1985 40,223 17

1986 44,408 18

1987 48,300 20

1988 49,928 20

1989 59,171 24

1990 65,526 27

1991 71,608 28

1992 80,259 31

1993 89,587 34

1994 95,034 36

1995 100,250 38

Percentage change,

1980-1995 311.5% 245.4%

Source: BJS.

1

The adult correctional population is the total number of adult offenders under some form of

supervision—prison, probation, parole, or jail—by the criminal justice system.

Page 23 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

Table II.2 shows the federal prison inmate population at fiscal year-end.

According to BOP, the population data presented are different than BJS’ data

(presented in table II.1) in that, in addition to being compiled by fiscal year

rather than calendar year, they represent inmates both in BOP facilities and

alternative confinements, such as contract facilities.

Table II.2: Federal Prison Inmate

Populations at Fiscal Year-End, 1980

Through 1995

Fiscal year Population

1980 24,640

1981 26,313

1982 30,531

1983 33,216

1984 35,795

1985 40,330

1986 46,055

1987 49,378

1988 50,513

1989 57,762

1990 64,936

1991 71,508

1992 79,678

1993 88,565

1994 95,162

1995 100,958

Percentage

change, 

1980-1995 309.7%

Source: BOP.

As table II.3 shows, from 1980 to 1995, the state prison inmate population

and the corresponding incarceration rate grew by about 236 and about 191

percent, respectively. In 1995, the state prison inmate population reached

just over 1 million, compared with just over 300,000 in 1980. The

incarceration rate reached 390 inmates for every 100,000 U.S. residents in

1995, compared with 134 in 1980. From 1980 to 1995, the prison

populations in California and Texas grew by well over 400 percent and

300 percent, respectively.

Page 24 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

Table II.3: State Prison Inmate

Populations and Incarceration Rates at

Year-End, 1980 Through 1995

Calendar year All states California Texas

Inmates per 100,000

U.S. residents, all

states

1980 305,458 24,569 29,892 134

1981 341,797 29,202 31,502 148

1982 384,133 34,640 36,149 165

1983 404,929 39,373 35,259 172

1984 427,739 43,197 36,682 180

1985 462,284 50,158 37,532 193

1986 500,584 59,484 38,534 207

1987 536,784 66,975 38,821 218

1988 577,672 76,171 40,437 234

1989 653,193 87,297 44,022 260

1990 708,393 97,309 50,042 280

1991 753,951 101,808 51,677 295

1992 802,241 109,496 60,487 313

1993 879,714 119,951 92,013 331

1994 960,039 125,605 118,195 367

1995 1,026,882 135,646 127,766 390

Percentage change,

1980-1995 236.2% 452.1% 327.4% 191.0%

Source: BJS.

Projected Prison

Inmate Populations

Table II.4 shows that the federal prison inmate population is projected by

BOP to continue growing, reaching over 125,000 inmates in 2000 and over

138,000 inmates in 2006. These projected populations represent increases

of about 25 and about 38 percent, respectively, over the 1995 level.

Page 25 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

Table II.4: Projected Federal Prison

Inmate Populations, 1996 Through

2006 Year

Projected

populationa

1996 105,128

1997 111,347

1998 116,762

1999 120,974

2000 125,144

2001 128,451

2002 130,908

2003 133,140

2004 135,006

2005 136,678

2006 138,120

aThese are point estimates generated by BOP’s model. The model does not generate confidence

intervals.

Source: BOP.

Table II.5 shows NCCD’s prison population projections through 2000 for the

21 states that use its Prophet population projection model, California

(which uses a similar model), and Texas, which provided its own

projections to NCCD. Using data for these 23 states, and assuming that the

sentencing policies in effect in 1994 would continue, NCCD estimated that

the federal and state prison inmate population could reach 1.4 million in

2000.

Page 26 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

Table II.5: Projected Prison Inmate

Populations for 23 States, 1996

Through 2000

Projected population, by yeara

State 1996 1997 1998 1999 2000

Arkansas 9,079 9,106 9,185 9,264 9,337

California 142,551 159,992 176,013 192,814 210,442

Colorado 12,261 13,308 14,326 15,455 15,455

Connecticut 12,989 13,301 13,458 13,684 13,999

Florida 72,357 73,999 75,493 76,512 77,896

Hawaii 2,102 2,290 2,415 2,540 2,261

Idaho 2,759 2,836 2,941 2,979 2,989

Illinois 41,726 43,586 46,105 48,561 51,216

Indiana 15,100 15,300 15,500 15,800 16,100

Kansas 7,045 6,997 6,839 6,637 6,637

Kentucky 12,320 13,072 14,518 15,227 15,987

Louisiana 28,000 29,500 31,000 32,500 34,000

Massachusetts 10,632 11,250 11,580 11,911 12,356

Michigan 44,073 45,796 47,580 49,440 51,365

Mississippi 12,194 12,684 13,184 13,664 14,170

Nevada 7,670 8,101 8,530 9,032 9,516

Ohio 43,059 43,915 44,850 46,080 47,215

Oklahoma 18,466 18,918 19,327 19,825 20,112

Oregon 7,472 8,600 9,764 11,440 13,116

Rhode Island 3,181 3,215 3,248 3,248 3,293

Tennessee 18,372 18,758 19,227 19,671 19,886

Texas 140,882 148,866 153,654 151,842 149,444

Virginia 31,700 34,659 38,050 39,005 40,984

Total 695,990 738,049 776,787 807,176 837,800

aThese are point estimates generated by NCCD’s model. The model does not generate

confidence intervals.

Source: NCCD.

Growth in Other Adult

Correctional

Populations

As table II.6 shows, the populations in all four adult correctional

categories—prison, probation, parole, and jail—have increased between

1980 and 1995. The total federal and state prison inmate population in

custody2

 grew by about 237 percent from 1980 to 1995. In comparison,

during the same period, the probation population grew by 176 percent, the

2

Populations in custody are those actually held in a state’s correctional facility. According to BJS, for

comparison purposes across correctional populations, custody figures are used for prison and jail

populations to avoid the double-counting of inmates.

Page 27 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

parole population grew by 218 percent, and the jail population grew by 178

percent.3

 Overall, the total adult correctional population grew by 192

percent, from 1.8 million in 1980 to about 5.4 million in 1995.4

 During this

time, the U.S. adult population grew by about 19 percent, from

163.5 million to about 194.0 million. Accordingly, the adult correctional

population represented 2.8 percent of the total adult population in 1995,

well over double the 1.1-percent level in 1980.

Table II.6: Adult Correctional

Populations by Category, 1980 and

1995

Population category 1980 1995

Percentage

population

increase from

1980 to 1995

Prison 319,598 1,078,545 237

Probation 1,118,097 3,090,626 176

Parole 220,436 700,174 218

Jail 182,288 507,234 178

Total adult correctional population 1,840,419 5,376,579 192

U.S. adult population 163,541,000 194,015,000 19

Source: GAO analysis of BJS data.

Figure II.1 shows that the populations in the four adult correctional

categories as a percentage of the total adult correctional population were

essentially unchanged between 1995 and 1980. Specifically, in 1995, the

prison inmate population represented 20 percent of the total adult

correctional population, compared with 17 percent in 1980. Also, in 1995,

the probation population represented 57 percent (61 percent in 1980), the

parole population 13 percent (12 percent in 1980), and the jail population

9 percent (10 percent in 1980) of the total adult correctional population.

3

Jail population data are as of June 30, 1996.

4

According to BJS, because some persons may have multiple statuses, the sum of persons incarcerated

(prison or jail) and under community supervision (probation or parole) overestimates the total

correctional population.

Page 28 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix II 

Trends in Federal and State Prison Inmate

Populations and Incarceration Rates

Figure II.1: Distribution of Adult

Correctional Populations, 1980 and

1995

Percent

0

10

20

30

40

50

60

70

80

90

100

Prison Probation Parole Jail

Correctional population categories

17 20

61

57

12 13 10 9

1980

1995

Source: GAO analysis of BJS data.

Page 29 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix III 

Trends in Federal and State Prison

Operating and Capital Costs

Prison Operating

Costs (Fiscal Years

1980 Through 1994)

Table III.1 shows that federal and state prison annual operating costs have

grown significantly (a combined 224 percent increase in inflation-adjusted

terms) since fiscal year 1980. These costs cumulatively totaled about

$137.7 billion in current dollars for fiscal years 1980 through 1994.

Table III.1: Federal and State Prison

Operating Costs in Current Dollars,

Fiscal Years 1980 Through 1994

Costs in thousands of current dollars

Fiscal year Federal State Totala

1980 $319,274 $2,787,369 $3,106,643

1981 346,517 3,229,234 3,575,751

1982 368,000 3,794,178 4,162,178

1983 435,000 4,346,273 4,781,273

1984 529,245 5,066,666 5,595,911

1985 500,941 5,934,160 6,435,101

1986 555,097 6,619,534 7,174,631

1987 580,120 7,601,594 8,181,714

1988 878,502 8,586,498 9,465,000

1989 900,334 9,611,020 10,511,354

1990 1,148,678 11,194,236 12,342,914

1991 1,318,741 12,514,171 13,832,912

1992 1,585,498 13,290,202 14,875,700

1993 1,767,019 14,239,710 16,006,729

1994 1,918,067 15,776,174 17,694,241

Totala $13,151,033 $124,591,019 $137,742,052

Note 1: Dollar figures represent actual dollars (no adjustment for inflation).

Note 2: According to BOP, the federal cost data presented are actual obligations, adjusted for

equipment and other capital item costs.

aDetails may not add to total due to rounding.

Source: BOP and U.S. Bureau of the Census.

Prison Capital Costs

(Fiscal Years 1980

Through 1994)

As table III.2 shows, federal and state prison capital costs have also grown

significantly from fiscal year 1980 to 1994. Total capital costs reached

about $2.3 billion in fiscal year 1994, an inflation-adjusted increase of

about 141 percent over the level in fiscal year 1980. Federal and state

capital costs cumulatively totaled about $25.4 billion for fiscal years 1980

through 1994.

Page 30 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix III 

Trends in Federal and State Prison

Operating and Capital Costs

Table III.2: Federal and State Prison

Capital Costs in Current Dollars, Fiscal

Years 1980 Through 1994

Costs in thousands of current dollars

Fiscal year Federal State Totala

1980 $21,766 $515,854 $537,620

1981 20,807 541,939 562,746

1982 6,500 604,715 612,215

1983 54,000 589,325 643,325

1984 42,072 792,963 835,035

1985 111,787 992,071 1,103,858

1986 145,382 1,473,544 1,618,926

1987 249,279 1,226,049 1,475,328

1988 544,392 1,715,463 2,259,855

1989 266,994 1,984,518 2,251,512

1990 1,505,953 2,175,823 3,681,776

1991 419,262 2,497,997 2,917,259

1992 475,733 2,057,383 2,533,116

1993 366,144 1,726,171 2,092,315

1994 311,687 1,965,763 2,277,450

Totala $4,541,758 $20,859,578 $25,401,336

Note 1: Dollar figures represent actual dollars (no adjustment for inflation).

Note 2: According to BOP, the federal cost data presented are actual obligations, adjusted for

equipment and other capital item costs.

aDetails may not add to total due to rounding.

Source: BOP and U.S. Bureau of the Census.

Table III.3 shows that federal and state prison operating and capital costs

cumulatively totaled about $163.1 billion in current dollars for fiscal years

1980 through 1994. Federal costs totaled about $17.7 billion, while state

costs totaled about $145.5 billion during this period. Operating costs

totaled about $137.7 billion, while capital costs totaled about $25.4 billion.

Table III.3: Federal and State Prison

Total Cumulative Costs in Current

Dollars, Fiscal Years 1980 Through

1994

Operating cost Capital cost Total

Federal $13,151,033 $4,541,758 $17,692,791

State 124,591,019 20,859,578 145,450,597

Total $137,742,052 $25,401,336 $163,143,388

Source: Summary of tables III.1 and III.2.

Page 31 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix III 

Trends in Federal and State Prison

Operating and Capital Costs

Projected Federal

Prison Operating and

Capital Costs

Table III.4 shows BOP’s projections for federal prison operating and capital

costs through fiscal year 2006. As shown, BOP projects that operating costs

in fiscal year 2006 could be almost double the 1996 level. The projections

also show that capital costs are expected to fluctuate on a year-by-year

basis.

Table III.4: Projected Federal Prison

Operating and Capital Costs, Fiscal

Years 1996 Through 2006

Costs in thousands of current dollars

Fiscal year Operating Capital Total

1996 $2,440,394 $445,903 $2,886,297

1997 2,843,292 506,552 3,349,844

1998 3,054,347 553,493 3,607,840

1999 3,365,142 424,136 3,789,278

2000 3,604,601 341,741 3,946,342

2001 3,805,956 303,576 4,110,532

2002 3,958,572 287,608 4,246,180

2003 4,163,304 282,823 4,446,127

2004 4,343,282 283,718 4,627,000

2005 4,528,328 287,555 4,815,883

2006 4,721,072 293,005 5,014,077

Note: According to BOP, projections of operating and capital budgets are based on estimated

obligations—as presented in the Office of Management and Budget’s fiscal year 1998 budget for

the federal government—adjusted for equipment and other capital item costs.

Source: BOP.

Page 32 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix IV 

Models and Methodologies Used for

Projecting Prison Inmate Populations

Various types of models and methodologies are used to project prison

inmate populations, but microsimulation is the model type most widely

used by federal and state corrections agencies.1

 As used by BOP and 27

states, including California and Texas, microsimulation modeling can

project prison populations by simulating a wide range of legislative, policy,

or administrative changes that affect the criminal justice system. Other

states use flow models or statistical methods to project populations.

Except for BOP’s projection model, we did not identify any independent

assessments of the validity or reliability of the various projection models.

However, self-reported data indicated that the models have been accurate.

Microsimulation

Modeling Is Most

Widely Used

Microsimulation models replicate the flow of persons through the criminal

justice system, incorporating considerable detail from the actual records

of convicted offenders. As table IV.1 shows, microsimulation modeling is

used by BOP and 27 states. In 1987, BOP and the U.S. Sentencing

Commission jointly developed the Federal Sentencing Simulation Model

(FEDSIM) to comply with a series of congressional initiatives that required

an impact analysis of federal sentencing guidelines. In January 1995, BOP

began using a revised model (FEDSIM-2), which incorporates different data

sets based upon experience under federal sentencing guidelines. The NCCD

Prophet model is based on a model that the California Department of

Corrections has used since 1976. The Texas Criminal Justice Policy

Council developed the JUSTICE microsimulation model in 1987. Each of

these three models is discussed separately in the following sections.

1

NCCD, which is a nongovernmental forecasting organization, also uses a microsimulation

model—NCCD Prophet.

Page 33 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix IV 

Models and Methodologies Used for

Projecting Prison Inmate Populations

Table IV.1: Types of Models Used by

BOP and States to Project Prison

Populations Model type User (BOP or state)a

Number of

users

Microsimulation

FEDSIM-2 Bureau of Prisons 1

NCCD Prophet Arizona, California, Colorado,

Connecticut, Florida, Hawaii, Idaho,

Illinois, Indiana, Kansas, Kentucky,

Louisiana, Maine, Massachusetts,

Michigan, Mississippi, Nevada, New

Jersey, Ohio, Oklahoma, Rhode

Island, Tennessee, Virginia 23

Otherb Georgia, Minnesota, North Carolina,

Texas 4

Flowc

IMPACT District of Columbia, Montana,

Nebraska, New Mexico, Vermont,

Wyoming 6

Other Pennsylvania, Oregon, Utah 3

Statistical methods (various)d Alabama, Alaska, Arkansas,

Delaware, Iowa, Maryland, Missouri,

New York, South Dakota, Wisconsin 10

Other (proprietary)e New Hampshire, South Carolina,

Washington 3

Total users N/A 50

Legend: N/A equals not applicable.

aState data exclude North Dakota and West Virginia because these states do not project inmate

populations.

bIncludes the JUSTICE model used in Texas.

cFlow models track the movement or “flow” of persons throughout each stage of the criminal

justice system, from arrest to parole. One flow model used by several states is the Interactive

Model for Projecting Arrest and Corrections Trends (IMPACT).

dVarious regression and time series analyses and techniques.

eProprietary models not classifiable as microsimulation, flow models, or statistical methods.

Source: Developed by GAO from data presented in Corrections Compendium (April 1996) and

NCCD FOCUS (July 1995), and discussions with BOP, NCCD, and state corrections agency

officials.

BOP’s Model (FEDSIM-2) Using convicted offenders’ cases, two data sets are used when FEDSIM-2 is

updated annually: (1) the total prison population at the end of the prior

fiscal year and (2) all inmates admitted into federal prisons during the

prior fiscal year. In this model, prospective release dates for individuals in

Page 34 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix IV 

Models and Methodologies Used for

Projecting Prison Inmate Populations

both groups are recorded, and sentencing time is distributed into monthly

groupings or “trace elements” to track the total time served for each

prisoner. FEDSIM-2 tracks convicted drug offenders,2

 along with 20 other

types of offenders, to determine the overall trend in the federal prison

population.

NCCD’s Model (Prophet) The Prophet model, which NCCD has customized to accommodate states’

correctional information systems, can predict future population levels,

isolate the effects of specific practices, and predict the effects of proposed

policy changes. This model is conceptually designed around the movement

of offenders into, through, and out of the prison and parole systems. As

shown in table IV.1, 23 states (including California) use a form of this

model. The Prophet model simulates offender subgroup compositions and

lengths of stays within each stage of the correctional system. Individual

cases are then processed through a series of probability distribution arrays

or matrices, which allows the model to compute prison populations.

Using the model, the total correctional population can be separated into

subgroups, and forecasts for each subgroup can be made on the basis of

the proposed policy changes, without altering the status of the other

subgroups. Prophet requires five data sets to operate—prison admissions,

prison exits, current prison population, current parole population, and

parole exits.

Texas’ Model (JUSTICE) Texas’ JUSTICE microsimulation model uses convicted felony offenders’

records from the state’s jail, prison, and parole populations. On a monthly

basis, these data are loaded into or updated in the model, which has two

parts. One part covers prisoners coming into the correctional system, and

the second part covers the policies that determine movement within the

system. Projections are made from the first part, and impact analyses of

proposed policy changes are made from the second part.

JUSTICE creates future offenders’ records by duplicating key characteristics

(e.g., offense and sentence) of the current admissions and parolees and

assessing the probability of these characteristics being present in future

admissions. The model accounts for the specific months that offenders

enter the different stages of the system and projects a total number of

adult felony arrests on the basis of the at-risk population—i.e., that portion

2

Since drug offenders constitute over one-half of the total federal prison population (60 percent in

1993), this category has been called the “tail that wags the dog.”

Page 35 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix IV 

Models and Methodologies Used for

Projecting Prison Inmate Populations

of the Texas population (aged 18 to 44 years old) considered most likely to

engage in criminal activity. Each offender’s key characteristics determine

the flow of the offender through the system by triggering certain criteria

(e.g., parole eligibility) that affect the time and direction of the offender’s

movement through the system.

The first part of the JUSTICE model is used to make projections of those

most likely to be sent to prison or placed on probation. The second part of

the model permits simulating the impact of proposed changes affecting the

size of the probation, prison, and parole populations. Texas’ JUSTICE model

has considerable flexibility in simulating changes in the major “rules of

movement” through the state’s correctional system. For example, 29

parameters can be interactively altered to assess the impact of proposed

policy changes.

Reliability of

Microsimulation

Models

According to experts in the prison modeling field, there are no standard

criteria for assessing or validating the reliability of microsimulation

models used to project prison populations. The NCCD and state agency

officials we contacted said that microsimulation models are generally

considered reliable if the projections come within 2 percent of the actual

populations. These officials also commented that projections beyond 5

years, and perhaps even beyond 2 years, are usually considered rough

estimates.

Notwithstanding that comparing projections with actual prison

populations may be an insufficient gauge of a model’s reliability, on the

basis of self-reported assessments, the three major models we identified

(FEDSIM-2, NCCD Prophet, and JUSTICE) are reported to produce accurate

projections. For instance, the April 1996 issue of the Corrections

Compendium presented the results of a survey about prison population

projections. In responding to a question in the survey related to projection

accuracy, BOP, California, and Texas reported that their respective

projections were accurate.

Other Models and

Methods

As shown in table IV.1, in contrast to the microsimulation models used by

BOP and most states, other states use flow models and statistical methods

to project prison populations. Flow models separate the characteristics of

the various groups or cohorts of prisoners moving through the system

from the aggregate population for analysis. These models track the

offenders through the criminal justice system by calculating percentages

Page 36 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix IV 

Models and Methodologies Used for

Projecting Prison Inmate Populations

(or branching ratios) of the offender population that continue through

each stage of the system. For example, of every 100 arrests, perhaps only

30 percent of the individuals will be indicted; and, of the indictments,

perhaps only 50 percent will be convicted; etc. In other words, flow

models represent continuation into the next stage, with branching ratios

used to “prune” out those offenders who will not become part of the

prison inmate population.

Also shown in table IV.1, 10 states use statistical methods, such as

regression analysis and time series analysis, to project prison populations.

Statistical methods all use data from past patterns to project future inmate

populations. Regression analysis, for example, is a statistical technique

based on equations that functionally relate one or more independent

variables, with coefficients determined from previous analysis, to a

dependent variable. Statistical methods tend to be nonpolicy sensitive and,

therefore, are not particularly useful for impact analyses. However,

reasons for changes can be deduced retrospectively from these statistical

methods.

Finally, as shown in table IV.1, three states use models or methodologies

that are not classifiable either as microsimulation, flow models, or

statistical methods. For example, one state projects its future population

by extrapolating the previous 5-year growth trend in the existing

population.

Page 37 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
Appendix V 

Major Contributors to This Report

General Government

Division, Washington,

D.C.

Seto J. Bagdoyan, Evaluator-in-Charge

David Thomas, Intern

David Alexander, Senior Social Science Analyst

Pamela V. Williams, Communications Analyst

Katherine M. Wheeler, Publishing Advisor

Office of the General

Counsel, Washington,

D.C.

Geoffrey R. Hamilton, Senior Attorney

Dallas Field Office Danny R. Burton, Assistant Director, Administration

 of Justice Issues

Mary K. Muse, Senior Evaluator

(182831) Page 38 GAO/GGD-97-15 Inmate Populations, Costs, Projection Models
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