Sourcebook of Criminal Justice Statistics
National Jail Census, Annual Survey of
Jails, and Survey of Inmates in Local Jails
Methodology and survey sampling procedures
Note: The following information was excerpted from the U.S. Department of Justice,
Bureau of Justice Statistics, Jails and Jail Inmates 1993-94, Bulletin
NCJ-151651 (Washington, DC: U.S. Department of Justice, April 1995), pp. 14-16; Prison
and Jail Inmates at Midyear 1997, Bulletin NCJ-167247 (Washington, DC: U.S.
Department of Justice, January 1998), pp. 9, 10; Profile of Jail Inmates, 1996,
Special Report NCJ-164620 (Washington, DC: U.S. Department of Justice, April 1998), pp.
13, 14; and information provided by the U.S. Department of Justice, Bureau of Justice
Statistics. Non-substantive editorial adaptations have been made.
National Jail Census
The National Jail Census is taken every 5 years and is conducted for the U.S.
Department of Justice, Bureau of Justice Statistics (BJS) by the U.S. Bureau of the
Census. Data are presented for censuses conducted in 1983, 1988, and 1993. For 1983,
questionnaires were mailed to all (3,358) locally administered jails in the Nation. For
1988, questionnaires were mailed to 3,448 locally administered jails. Forty-four jails
were added to the initial mailing and 176 were deleted, yielding a final count of 3,316
facilities for 1988. Through the use of various followup procedures, a response rate of
99% was achieved for 1983, and 100% for 1988.
The most recent census, conducted in 1993, included all locally administered
confinement facilities (3,287) that hold inmates beyond arraignment and are staffed by
municipal or county employees. The census also included 17 jails that were privately
operated under contract for local governments and 7 facilities maintained by the Federal
Bureau of Prisons and functioning as jails.
Excluded from the census were temporary holding facilities, such as drunk tanks and
police lockups, that do not hold persons after being formally charged in court (usually
within 72 hours of arrest). Also excluded were State-operated facilities in Alaska,
Connecticut, Delaware, Hawaii, Rhode Island, and Vermont, which have combined jail-prison
systems. Five locally operated jails in Alaska were included.
The mailing list used for the census was derived from the National Justice Agency List
maintained by the U.S. Bureau of the Census for BJS. The census forms were mailed to 3,506
facilities on June 22, 1993. Twenty-eight jails were added to the initial mailing and 230
were deleted, resulting in a total of 3,304 facilities.
After extensive followup, including additional mail requests and repeated telephone
contacts, all jails (except those in one jurisdiction) provided data for four critical
data items--number of inmates, average daily population, rated capacity, and sex of
inmates housed. Data on these four items for the nonresponding jails were imputed based on
data reported in the 1994 Annual Survey of Jails.
Completed forms with data for all or most items were received for 2,981 jails,
resulting in a 90% response rate. These reporting jails housed 93% of all local jail
inmates on June 30, 1993. Because there was nonresponse and incomplete data on all census
items except the four critical items, national totals had to be estimated. Readers
interested in the estimation procedures employed should consult the original Source
(Source, Jails and Jail Inmates 1993-94).
Annual Survey of Jails
In each of the 4 years between the full censuses, a survey of jails is conducted to
estimate baseline characteristics of the Nation's jails and inmates housed in the jails.
Data from the Annual Survey of Jails are presented for 1984-87, 1989-92, and 1994-97. The
reference date for each of these surveys was June 30, except 1990 when the reference date
was June 29, and 1991 and 1996 when it was June 28. All surveys prior to the 1994 survey
were based on all jails in jurisdictions with 100 or more jail inmates and a stratified
random sample of jurisdictions with an average daily population of less than 100 inmates.
For 1984, 1,164 jails in 893 jurisdictions were included; in 1985, 1,142 jails in 874
jurisdictions were included; in 1986, 1,137 jails in 868 jurisdictions were included; in
1987, 1,135 jails in 866 jurisdictions were included; in 1989, 1,128 jails in 809
jurisdictions were included; in 1990, 1,135 jails in 804 jurisdictions were included; in
1991, 1,124 jails in 799 jurisdictions were included; and in 1992, 1,113 jails in 795
jurisdictions were included.
A new sample of jail jurisdictions was selected for the 1994-97 surveys using
information from the 1993 census. A jurisdiction is a county (parish in Louisiana) or
municipal government that administers one or more local jails. The 1997 sample included
all jails in 795 selected jail jurisdictions and 25 multijurisdiction jails. A
multijurisdiction jail is one in which two or more jurisdictions have a formal agreement
to operate the facility.
In drawing the samples for 1994-97, jail jurisdictions were first stratified into two
groups: single jurisdiction jails and multijurisdiction jails. All of the
multijurisdiction jails were included in the survey. The remaining jurisdictions were then
further stratified into two groups: jurisdictions with jails authorized to hold juveniles
and jurisdictions with jails holding only adults. Jurisdictions were then selected based
on the average daily population in the 1993 census. In 1997, all jails in 204
jurisdictions were automatically included if the jurisdiction held juveniles and had an
average daily population of 250 or more inmates in 1993 or if they held only adults and
had an average population of 500 or more. The other jurisdictions (591) were then selected
based on stratified probability sampling.
Data were obtained by mailed questionnaires. After followup phone calls to
nonrespondents, the response rate for the 1997 survey was 100%.
Survey estimates have an associated sampling error because jurisdictions with smaller
average daily populations were sampled for the survey. Estimates based on the sample
survey may differ somewhat from the results of conducting a complete census. Different
samples could yield somewhat different results. Standard error is a measure of the
variation among the estimates from all possible samples, stating the precision with which
an estimate from a particular sample approximates the average of all possible samples. The
estimated relative sampling error for the total number of persons under the jurisdiction
of jail authorities of 637,319 on June 30, 1997, was 0.86%; for persons held in the custody
of jail authorities of 567,079, was 0.64%. Readers interested in standard error estimates
should consult the original Source (Source, Prison and Jail Inmates at Midyear 1997).
Measures of population
Two measures of inmate population are used: the average daily population for the year
ending June 30 and the inmate count on June 30 of each year. The average daily population
balances out any extraordinary events that may render atypical the inmate count on June
30. The June 30 count provides data on characteristics of inmates, such as race, Hispanic
origin, and age, that may not be available on an annual basis.
For the first time, in 1995 the Annual Survey of Jails obtained separate counts of the
total number of offenders under jail jurisdiction, those held in jail facilities, and
those supervised outside of jail facilities. Previous surveys and censuses included a
small but unknown number of offenders under community supervision. To estimate the percent
change from 1994 to 1995 in the jail population, the 1995 survey included a count of
inmates held at midyear 1994.
In the 1996 survey the number of persons supervised outside a jail facility included
for the first time persons under drug, alcohol, mental health, or other medical treatment.
Comparison with 1995 estimates should exclude these persons.
State statutes and judicial practices allow juveniles to be incarcerated in adult jails
under a variety of circumstances. Because of differing statutes and practices, however,
accurate and comparable data on juveniles are difficult to collect. Beginning in 1994, the
Annual Survey of Jails provided estimates of the total number of jail inmates under age
18, the number held as adults, and the number held as juveniles. New sampling procedures
also were introduced in 1994 to minimize the standard errors of these estimates. By
stratifying jurisdictions based on the authority to house juveniles, the precision of the
juvenile counts was improved.
Survey of Inmates in Local Jails
The 1996 Survey of Inmates in Local Jails was conducted for BJS by the U.S. Bureau of
the Census. Similar surveys of jail inmates were conducted in 1972, 1978, 1983, and 1989.
Interviews for the 1996 survey were conducted from October 1995 through March 1996.
Interviews were about an hour long and used computer-assisted personal interviewing
(CAPI). With CAPI, computers provide the interviewer questions, including followup
questions tailored to preceding answers. Before the interview inmates were told verbally
and in writing that participation was voluntary and that all information provided would be
held in confidence. Participants were assured that the survey was solely for statistical
purposes and that no individual could be identified through use of survey results.
The sample for the 1996 survey was selected from a universe of 3,328 jails that were
enumerated in the 1993 Census of Jails or opened after the Census but before the spring of
1996. The sample design was stratified two-stage selection. In the first stage six
separate strata were formed based on the size of the male and female populations. In two
strata all jails were selected--those jails housing only females and those with more than
1,000 males or more than 50 females or both. In the remaining four strata a systematic
sample of jails was selected. Each jail within a stratum had an equal probability of
selection. Equal probabilities were used instead of probability proportional to size
because jail populations were likely to change between 1993 and 1995. Overall, 462 jails
were selected. Interviews were conducted in 431; 19 refused, 8 were closed, and 4 were on
the universe list in error.
In the second sampling stage, interviewers visited each selected facility and
systematically selected a sample of male and female inmates using predetermined
procedures. As a result, approximately 1 in every 100 males were selected in 4 strata and
1 in 83 in the male stratum. Depending on the stratum, 1 in 50, 25, 24, or 21 females were
selected. A total of 6,133 inmates were interviewed, and 738 refused to participate, for a
second stage nonresponse of 10.8%. The total nonresponse from both stages was 13.7%.
Based on the completed interviews, estimates for the entire population were developed
using weighting factors derived from the original probability of selection in the sample.
These factors were adjusted for variable rates of nonresponse across strata and inmate
characteristics. Further adjustments were made to control the survey estimates to counts
of jail inmates obtained from the 1993 Census of Jails and the 1995 Annual Survey of
Accuracy of the survey estimates
The accuracy of the estimates from the 1996 Survey of Inmates in Local Jails depends on
two types of error: sampling and measurement. Sampling error is variation that may occur
by chance because a sample rather than a complete enumeration of the population was
conducted. Measurement error can be attributed to many sources, such as nonresponse,
differences in the interpretation of questions among inmates, recall difficulties, and
processing errors. In any survey the full extent of the measurement error is never known.
Conviction status--In the 1996 survey, inmates still serving sentence for an
offense--that is, on probation, parole, or other conditional release--when most recently
admitted to jail were classified as sentenced. In prior surveys, status was based on the
offense for which they were most recently admitted to jail. For the 1996 survey 55.2% were
classified as sentenced, but that percentage would have been 45.9% under the
classification of previous surveys.
Educational attainment--Starting with the 1996 survey, inmates who had not
finished high school were asked if they had earned a GED or high school equivalency
certificate, which was classified as a high school diploma. This change raised the
percentage of high school graduates from 25.9% to 30.0%. GED responses were volunteered by
respondents in prior surveys.