National Inmate Survey, 2008-2009 (ICPSR 34510)

Time Period(s) View help for Time Period(s)

Date of Collection View help for Date of Collection

Data Collection Notes View help for Data Collection Notes

Study Purpose View help for Study Purpose

The Prison Rape Elimination Act of 2003 (P.L. 108-79) requires the Bureau of Justice Statistics (BJS) to carry out a comprehensive statistical review and analysis of the incidence and effects of prison rape for each calendar year.

Study Design View help for Study Design

The interviews, which averaged 25 minutes in length, used computer-assisted personal interviewing (CAPI) and audio computer-assisted self-interviewing (ACASI) data collection methods. For approximately the first two minutes, survey interviewers conducted a personal interview using CAPI to obtain background information and date of admission to the facility. For the remainder of the interview, respondents interacted with a computer-administered questionnaire using a touch-screen and synchronized audio instructions delivered via headphones. Respondents completed the ACASI portion of the interview in private, with the interviewer either leaving the room or moving away from the computer.

A shorter paper questionnaire was made available for inmates who were unable to come to the private interviewing room or interact with the computer. The paper form was completed by 496 prison inmates (or 1.5 percent of all prison interviews), 226 jail inmates (0.5 percent), and 4 military inmates (1 percent). Most of these inmates were housed in administrative or disciplinary segregation or were considered too violent to be interviewed. No inmates in Indian country or ICE facilities completed the paper questionnaire.

Before the interview, inmates were informed verbally and in writing that participation was voluntary and that all information provided would be held in confidence. Interviews were conducted in either English (98 percent in prisons, 95 percent in jails, 40 percent in ICE facilities, and 100 percent in military and Indian country facilities) or Spanish (2 percent in prisons, 5 percent in jails, and 60 percent in ICE facilities).

Sample View help for Sample

Part I (Jails and Special Confinement Facilities)

Selection of jail facilities

A sample of 320 jails was drawn to represent approximately 10 percent of the 3,007 jail facilities identified in the Census of Jail Inmates, 2005. The 2005 census was a complete enumeration of all jail jurisdictions, including all publicly operated and privately operated facilities under contract to jail authorities. The NIS-2 was restricted to jails that had five or more inmates on June 30, 2005. Based on estimates from the Annual Survey of Jails, 2008, these jails held an estimated 777,200 inmates age 18 or older on June 30, 2008.

Jail facilities were sequentially sampled with probabilities of selection proportionate to size (as measured by the number of inmates held on June 30, 2005). Eight facilities that were unable to participate in NIS-1 were selected with certainty, while the measures of size of facilities that participated in NIS-1 were reduced to give them a lower probability of selection. The remaining facilities were stratified such that facilities in each of the 10 largest jail jurisdictions were placed into strata; all other facilities were placed in a single stratum. Within the large jurisdiction stratum, three facilities were selected from the five largest jurisdictions with probability proportionate to size, and two facilities were selected from the next five largest jurisdictions with probability proportion to size. Facilities in the second stratum were first sorted by region, state, and public or private operation. Facilities were sampled to ensure that at least one jail facility in every state was selected. The remaining jail facilities were selected from each region with probabilities proportionate to size.

Of the 320 selected jails in NIS-2, 10 facilities refused to participate:

• Baldwin Co. Corrections Center (AL)
• Marengo Co. Detention Center (AL)
• Merced Co. Jail (CA)
• Columbia Co. Detention Center (FL)
• Pike Co. Law Enforcement Center (IN)
• Flathead Co. Detention Center (MT)
• Rutherford Co. Jail (NC)
• Monmouth Co. Correctional Institution (NJ)
• Hildalgo Co. Detention Center (TX)
• Kenosha Co. Jail (WI)

Nine facilities were unable to participate due to lack of space, staffing shortages, or construction, but expect to be included in NIS-3 (to be conducted in 2011). Fifteen facilities were determined to be ineligible: seven had closed, four were community-based facilities, two had fewer than five inmates, and two were prisons. All other selected jail facilities participated fully in the survey.

Selection of inmates within jails

The number of inmates sampled in each facility varied based on six criteria:

• an expected prevalence rate of sexual victimization of 3 percent.
• a desired level of precision based on a standard error of 1.4 percent.
• a projected 65 percent response rate among selected inmates.
• a 5 percent chance among participating inmates of not receiving the sexual victimization questionnaire.
• an adjustment factor of 1.75 to account for the complex survey design.
• a pre-arraignment adjustment factor equal to 1 in facilities where the status was known for all inmates and less than 1 in facilities where only the overall proportion of inmates who were pre-arraigned was known.

A roster of inmates was obtained just prior to the start of interviewing at each facility. Inmates under age 18 and inmates who had not been arraigned were removed from the roster. Each eligible inmate was assigned a random number and sorted in ascending order. Inmates were selected from the list up to the expected number of inmates determined by the sampling criteria. Due to the dynamic nature of jail populations, a second roster of inmates was obtained on the first day of data collection. Eligible inmates who appeared on the second roster but who had not appeared on the initial roster were identified. These inmates had been arraigned since the initial roster was created or were newly admitted to the facility and arraigned. A random sample of these new inmates was chosen using the same probability of selection used to sample from the first roster.

A total of 81,306 jail inmates was selected. After selection, an additional 9,490 ineligible inmates were excluded -- 7,844 (9.7 percent) were released or transferred to another facility before interviewing began, 455 (0.6 percent) were mentally or physically unable to be interviewed, 144 (0.2 percent) were under age 18 or their age could not be obtained during the interview process, 308 (0.4 percent) were selected in error (i.e., an inmate was incorrectly listed on the facility roster), and 739 (0.9 percent) were on unsupervised work release or only served time on weekends.

Of all selected inmates, 17 percent refused to participate in the survey, 4 percent were not available to be interviewed (e.g., in court, in medical segregation, determined by the facility to be too violent to be interviewed, or restricted from participation by another legal jurisdiction), and 8 percent were not interviewed due to survey logistics (e.g., language barriers, releases, and transfers to another facility after interviewing began).

Overall, 48,066 jail inmates participated in the survey, yielding a response rate of 68 percent. Approximately 95 percent of the participating inmates (45,126) received the sexual assault survey.

Selection of special confinement facilities

A sample of 11 special facilities was drawn to represent the inmate populations in military, Indian country, and ICE facilities. Three military, three Indian country, and five ICE facilities were included. The selected military facilities were the largest Army, Navy, and Marine facilities, including the United States Disciplinary Barracks (Leavenworth, KS), the Naval Consolidated Brig. (Miramar, CA), and the Marine Corps Base Brig. (Camp Pendleton, CA).

The selected Indian country facilities were the three largest facilities identified in the 2007 Survey of Jails in Indian Country. One facility, Tohono O'odham Detention Center (AZ) was undergoing major renovations to accommodate increased capacity and could not participate in the survey during the data collection period. This facility will be included in the NIS-3 data collection. The Navajo Department of Corrections Window Rock (AZ), participated in the survey but held fewer inmates in 2009 (14) than reported in the 2007 survey (99).

The 5 ICE facilities were sequentially sampled from the 22 facilities run by ICE with probabilities of selection proportionate to size (as measured by the number of persons held at year-end 2008). Facilities were sorted by region and state.

Selection of inmates in special confinement facilities

For purposes of inmate selection, military facilities were treated as prisons, and Indian country and ICE facilities were treated like jails. The assumptions used to determine the sample size within a prison or jail and the corresponding selection procedures were used. However, in ICE facilities, a second sample of newly admitted inmates was not drawn due to an inability to identify new inmates on the ICE rosters. In addition, inmates in ICE facilities who did not speak English or Spanish were defined as ineligible for the study.

Overall, 2,494 inmates were selected, including 546 in military facilities, 161 in Indian country facilities, and 1,787 in ICE facilities. After selection, 409 ineligible inmates were excluded -- 225 (9 percent) were released or transferred to another facility before interviewing began, 10 (0.4 percent) were mentally or physically unable to be interviewed, 4 (0.2 percent) were on unsupervised work release, and 170 (7 percent) in ICE facilities did not speak English or Spanish. A total of 16 inmates were excluded in military facilities, 15 in Indian country facilities, and 378 in ICE facilities.

Of all selected inmates in special facilities, 16 percent refused to participate in the survey, 0.2 percent were not available to be interviewed (e.g., in court, in medical segregation, determined by the facility to be too violent to be interviewed, or restricted from participation by another legal jurisdiction), and 7 percent were not interviewed due to survey logistics (e.g., language barriers, releases, and transfers to another facility after interviewing began).

Overall, 1,471 inmates participated in the survey (399 30 August 2010 in military, 115 in Indian country, and 957 in ICE facilities), yielding a response rate of 71 percent (75 percent in military, 79 percent in Indian country, and 68 percent in ICE facilities). Approximately 95 percent of the participating inmates (1,379) received the sexual assault survey (379 in military, 107 in Indian country, and 893 in ICE facilities).

Part II (State and Federal Prisons)

Selection of state and federal prisons

A sample of 171 state and federal prisons was drawn to produce a sample representing approximately 10 percent of the 1,260 state and 192 federal adult confinement facilities identified in the 2005 Census of State and Federal Adult Correctional Facilities. The 2005 census was a complete enumeration of state prisons, including all publicly operated and privately operated facilities under contract to state correctional authorities. The NIS-2 was restricted to confinement facilities -- institutions in which fewer than 50 percent of the inmates were regularly permitted to leave, unaccompanied by staff, for work, study, or treatment. Such facilities included prisons, penitentiaries, prison hospitals, prison farms, boot camps, and centers for reception, classification, or alcohol and drug treatment. The NIS-2 excluded community-based facilities, such as halfway houses, group homes, and work release centers. Based on estimates from 2008 National Prisoner Statistics, the prisons in the study universe held an estimated 1,267,400 state and 190,300 federal inmates age 18 or older on June 30, 2008.

State and federal confinement facilities were sequentially sampled with probabilities of selection proportionate to size (as measured by the number of inmates held in state prisons on December 30, 2005, and in federal prisons on September 28, 2006). Facilities on the sampling frame were stratified by gender of inmates housed. The measures of size for facilities that participated in NIS-1 in 2007 were reduced to lower their probability of selection in NIS-2. Within each stratum, facilities on the sampling frame were first sorted by region, state, and public or private operation. The sample size for facilities housing only female inmates was set to 36 facilities to ensure a sufficient number of women and allow for meaningful analyses of sexual victimization by gender. Facilities were sampled ensuring that at least one facility in every state was selected. Federal facilities were grouped together and treated like a state for sampling purposes. The remaining facilities were selected from each region with probabilities proportionate to size.

Of the 171 selected prison facilities, 4 were deemed ineligible and excluded from the survey for the following reasons:

• Albion Correctional Facility (NY) -- Ongoing litigation.
• Robert Scott Correctional Facility (MI) -- Ongoing litigation.
• Dinwiddie Correctional Unit (VA) -- Closed prior to the start of data collection.
• Waseca FCI (BOP) -- Transitioned from holding males to females during the data collection period (treated as a closed facility).

All other selected prison facilities participated fully in the survey.

Selection of inmates within prisons

The number of inmates sampled in each facility varied based on six criteria:

• an expected sexual victimization prevalence rate of 4 percent;
• a desired level of precision based on a standard error of 1.75 percent;
• a projected 70 percent response rate among selected inmates;
• a 5 percent chance among participating inmates of not receiving the sexual victimization questionnaire.
• an adjustment factor of 1.75 to account for the complex survey design;
• the size of the facility.

A roster of inmates was obtained just prior to the start of interviewing at each facility. Inmates under age 18 and inmates expected to be released prior to data collection were deleted from the roster. Each eligible inmate was assigned a random number and sorted in ascending order. Inmates were selected from the list up to the expected number of inmates determined by the sampling criteria.

A total of 46,189 prison inmates were selected. After selection, 1,302 ineligible inmates were excluded -- 936 (2 percent) were released or transferred to another facility before interviewing began, 246 (0.5 percent) were mentally or physically unable to be interviewed, 13 (0.02 percent) were under age 18 or their age could not be obtained during the interview process, 11 (0.02 percent) were selected in error (i.e., an inmate was incorrectly listed on the facility roster), and 96 (0.2 percent) were on unsupervised work release or only served time on weekends.

Of all selected eligible prison inmates, 23 percent refused to participate in the survey, 2 percent were not available to be interviewed (e.g., in court, in medical segregation, determined by the facility to be too violent to be interviewed, or restricted from participation by another legal jurisdiction), and 2 percent were not interviewed due to survey logistics (e.g., language barriers, releases, or transfers to another facility after interviewing began).

Overall, 32,029 prison inmates participated in the survey, yielding a response rate of 71 percent. Approximately 95 percent of the participating inmates (29,954) received the sexual assault survey.

Universe View help for Universe

Part I: Inmates in local jails and in special confinement facilities (Indian country, and Immigration and Customs Enforcement facilities) in the United States. Part II: Inmates in state and federal adult confinement facilities (including military facilities).

Unit(s) of Observation View help for Unit(s) of Observation

Data Source View help for Data Source

Data Type(s) View help for Data Type(s)

Mode of Data Collection View help for Mode of Data Collection

Original Release Date View help for Original Release Date

2014-01-15

Version History View help for Version History

Weight View help for Weight

Responses from interviewed inmates were weighted to provide national-level and facility-level estimates. Each interviewed inmate was assigned an initial weight corresponding to the inverse of the probability of selection within each sampled facility. A series of adjustment factors was applied to the initial weight to minimize potential bias due to non-response and to provide national estimates.

Bias occurs when the estimated prevalence is different from the actual prevalence for a given facility. In each facility, bias could result if the random sample of inmates did not accurately represent the facility population. Bias could also result if the non-respondents were different from the respondents. Post-stratification and non-response adjustments were made to the data to compensate for these two possibilities. These adjustments included:

1. Calibration of the weights of the responding inmates within each facility so that the estimates accurately reflected the facility's entire population in terms of known demographic characteristics. These characteristics included distributions by inmate age, sex, race, time since admission, and sentence length. This adjustment ensures that the estimates better reflect the entire population of the facility and not just the inmates who were randomly sampled.

2. Calibration of the weights so that the weight from a non-responding inmate is assigned to a responding inmate with similar demographic characteristics. This adjustment ensures that the estimates accurately reflect the full sample, rather than only the inmates who responded.

For each inmate, these adjustments were based on a generalized exponential model, developed by Folsom and Singh, and applied to the sexual assault survey respondents.

A final ratio adjustment to each inmate weight was made to provide national-level estimates for the total number of inmates ages 18 or older who were held at mid-year 2008. These ratios represented the estimated number of inmates by sex (from BJS's 2008 Annual Survey of Jails and 2008 National Prisoner Statistics, Midyear) divided by the number of inmates by sex in the NIS-2 after calibration for sampling and non-response. The national estimates for state prisons were 1,178,916 males and 88,518 females; for federal prisons, 178,153 males and 12,120 females; and for jails (with an average daily population of 6 or more inmates), 678,136 males and 99,096 females.

Final ratio adjustments were not applied to inmate weights in military, Indian country, and ICE facilities. Estimates for special confinement facilities were made at the facility level only.