National Inmate Survey, 2011-2012 (ICPSR 35009)

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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.

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The interviews, which averaged 35 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 touchscreen 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 751 prison inmates (or 1.9 percent of all prison interviews)--733 were completed by adult prison inmates (1.9 percent of adult prison inmate interviews) and 18 were completed by prisoners ages 16 to 17 (3.4 percent of all prison inmate interviews of inmates ages 16 to 17). The paper questionnaire was also completed by 264 jail inmates (0.5 percent of all jail inmate interviews)--255 were completed by adults (0.5 percent of adult jail inmate interviews) and 9 were completed by jail inmates ages 16 to 17 (0.7 percent of jail inmate interviews of inmates ages 16 to 17). In addition, five paper questionnaires were completed by military inmates (0.9 percent of all military inmate interviews). Most of these inmates were housed in administrative or disciplinary segregation or were considered too violent to be interviewed

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 (96 percent in prisons, 95 percent in jails, 35 percent in ICE facilities, and 100 percent in military and Indian country facilities) or Spanish (4 percent in prisons, 5 percent in jails, and 65 percent in ICE facilities).

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Part I (Jails and Special Confinement Facilities - Adults)

Selection of jail facilities

A sample of 393 jails was drawn to represent the 2,957 jail facilities identified in the Census of Jail Inmates, 2005, and the sample was supplemented with information obtained during the NIS-1 and NIS-2. 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-3 was restricted to jails that had six or more inmates on June 30, 2005. Jails identified as closed or ineligible during the NIS-1 and NIS-2 were removed from the NIS-3 frame. Based on estimates from the Annual Survey of Jails, 2011, the jails in the NIS-3 held an estimated 720,171 inmates age 18 or older and 5,700 inmates ages 16 to 17 on June 30, 2011.

Jail facilities were sequentially sampled with probabilities of selection proportionate to size (as measured by the number of inmates held on June 30, 2005). Two facilities that were unable to participate in NIS-2 were selected with certainty, while the measures of size of facilities that participated in NIS-1 or NIS-2 were reduced to give them a lower probability of selection. Facilities with juveniles had their measures of size adjusted to increase their probability of selection. 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 probabilities proportionate to size, and two facilities were selected from the next five largest jurisdictions with probabilities proportionate 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 393 selected jails in NIS-3, 20 facilities refused to participate:

• Covington Co. Jail (AL)
• Mobile Co. Metro Jail (AL)
• Delaware Co. George W. Hill Corr. Fac. (PA)
• Montcalm Co. Jail (MI)
• Will Co. Adult Det. Fac. (IL)
• Northumberland Co. Prison (PA)
• Kenosha Co. Pre-Trial Det. Fac. (WI)
• Carroll Co. Jail (TN)
• Brevard Co. Jail (FL)
• Pinellas Co. North Division (FL)
• Hillsborough Co. Falkenburg Road Jail (FL)
• Paulding Co. Det. Ctr. (GA)
• Whitfield Co. Jail (GA)
• Marion Co. Jail (TN)
• Sandoval Co. Det. Ctr. (NM)
• Williamson Co. Jail (TX)
• Montgomery Co. Jail (NC)
• Catahoula Parish Corr. Ctr. (LA)
• Escambia Co. Det. Ctr. (AL)
• Orleans Parish House of Det. (LA).

Williamsburgh Co. Jail (SC) was excused due to construction at the facility. In Nassau Co. Corr. Ctr. (NY), data were collected only among inmates ages 16 to 17 due to lack of space to interview both adults and juveniles ages 16 to 17. Fourteen facilities were determined to be ineligible: six had closed, two were considered part of another inmate on the sampling frame, three had fewer than six eligible inmates, two were facilities containing only unsupervised work release inmates, and one had active litigation related to sexual victimization. All other selected jail facilities participated fully in the survey.

Selection of adult inmates within jails

A roster of inmates was obtained just prior to the start of interviewing at each facility. Inmates age 15 or younger and inmates who had not been arraigned were removed from the roster. Eligible inmates within a facility were placed into one of two stratum based on their age. Inmates who were 16 to 17 (juveniles) were placed in one stratum and inmates age 18 or older (adults) were placed in the other. Inmates age 15 or younger were considered ineligible for the NIS-3.

The number of adult 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 10 percent chance among participating inmates of not receiving the sexual victimization questionnaire.
• an adjustment factor of 1.9 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.

Each eligible adult 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 adult 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 112,594 adult and juvenile jail inmates were selected. After selection, an additional 11,342 ineligible inmates were excluded -- 9,479 (8.4 percent) were released or transferred to another facility before interviewing began, 1,036 (0.8 percent) were mentally or physically unable to be interviewed, 25 (0.02 percent) were age 15 or younger or their age could not be obtained during the interview process, 296 (0.3 percent) were selected in error (i.e., an inmate was incorrectly listed on the facility roster), and 484 (0.4 percent) were on unsupervised work release or only served time on weekends.

Of all selected inmates, 22 percent refused to participate in the survey, 1.1 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, 61,351 adult and juvenile jail inmates participated in the survey, yielding a response rate of 61 percent. Approximately 90 percent of the participating inmates (54,137) received the sexual assault survey. Among adult jail inmates, 52,926 responded to the sexual assault survey.

Selection of special confinement facilities

A sample of 16 special facilities was drawn to represent the inmate populations in military, Indian country, and ICE facilities. Five military, six Indian country, and five ICE facilities were included.

The military frame came from the military correctional facilities population report on April 1, 2011. The Indian country frame came from the BJS report, Jails in Indian Country, 2009, NCJ 232223, BJS Web, February 2011. The ICE frame came from the ICE integrated decision support system on March 21, 2011.

Military, Indian country, and ICE facilities were sequentially selected with probability proportionate to the adjusted number of inmates in the facility. The measures of size (population) were adjusted to reduce the probability of selection among facilities included in the NIS-2.

Tohono O'odham Adult Detention Facility (AZ) refused to participate in the NIS-3. All other selected special confinement facilities participated fully in the survey.

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, 2,874 inmates were selected, including 910 in military facilities, 300 in Indian country facilities, and 1,664 in ICE facilities. After selection, 163 ineligible inmates were excluded--28 (1.0 percent) were released or transferred to another facility before interviewing began, 46 (1.1 percent) were mentally or physically unable to be interviewed, 3 (0.1 percent) were sampled in error, 2 (0.1 percent) were inmates in custody only on the weekend, and 84 (3.0 percent) in ICE facilities did not speak English or Spanish.

Overall, 1,272 inmates participated in the survey (605 in military, 192 in Indian country, and 663 in ICE facilities), yielding a response rate of 68 percent in military, 68 percent in Indian country, and 43 percent in ICE facilities. Approximately 90 percent of the participating inmates (1,379) received the sexual victimization survey (539 in military, 160 in Indian country, and 573 in ICE facilities).

Part II (State and Federal Prisons - Adults)

Selection of state and federal prisons

A sample of 241 state and federal prisons was drawn to produce a sample representing the 1,158 state and 194 federal adult confinement facilities identified in the 2005 Census of State and Federal Adult Correctional [Facilities, supplemented with updated information from websites maintained by each state's department of corrections (DOC) and the Federal Bureau of Prisons (BOP). The 2005 census was a complete enumeration of adult state prisons, including all publicly operated and privately operated facilities under contract to state correctional authorities.

The NIS-3 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-3 excluded community-based facilities, such as halfway houses, group homes, and work release centers.

Based on BJS's 2011 National Prisoner Statistics and 2005 Census of State and Federal Adult Correctional Facilities, the prisons in the study universe held an estimated 1,238,000 state and 203,800 federal inmates age 18 or older and 1,700 state inmates ages 16 to 17 at yearend 2011. Facilities that had been closed and new facilities that had opened since the 2005 census were identified via review of DOC and BOP websites. Facilities determined to be closed were removed from the NIS-3 frame and new facilities were added.

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 9, 2010). Facilities on the sampling frame were stratified by sex of inmates housed, whether the facility had a mental health function, and whether the facility held five or more juveniles:

• Among facilities that housed males, the measure of size for facilities that held male inmates and participated in the NIS-1 in 2007 or NIS-2 in 2008-09 were adjusted to lower their probability of selection in the NIS-3.
• Among facilities with an inmate population that was at least 50 percent female, the measure of size for facilities that participated in the NIS-2 was reduced to lower their probability of selection in the NIS-3.
• The measures of size were further adjusted to increase the probability of selection of facilities with large juvenile populations.

Within each stratum, facilities on the sampling frame were first sorted by region, state, and public or private operation.

• The sample measures of size for facilities housing only female inmates were increased by a factor of 5 to ensure a sufficient number of women and allow for meaningful analyses of sexual victimization by sex. This led to an allocation of 51 female facilities (out of 233) in the sample.
• An additional 25 facilities were allocated to the stratum with facilities that have a mental health function, and another 20 facilities were allocated to the strata that housed juveniles.
• This led to the allocation of 66 facilities known to have a mental health function--49 male facilities and 17 female facilities--and 38 facilities that housed juveniles (36 facilities that housed males and 2 facilities that housed females).

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 241 selected prison facilities, 7 had closed prior to the start of data collection: Metro State Prison (GA), Hillsborough Corr. Inst. (FL), Gates Corr. Inst. (CT), Brush Corr. Fac. (CO), Burnet Co. Intermediate Sanction Fac. (TX), and Diamondback Corr. Fac. (OK). One facility--Chittenden Regional Corr. Fac. (VT)--had transitioned from holding males to females during the data collection period and was considered a closed facility. All other selected prison facilities participated fully in NIS-3.

Selection of adult inmates within prisons

A roster of inmates was obtained just prior to the start of data collection at each facility. Inmates age 15 or younger and inmates who were released prior to data collection were deleted from the roster. Eligible inmates within a facility were placed into one of two strata based on their ages. Inmates who were ages 16 to 17 (juveniles) were placed in one stratum and inmates age 18 or older (adults) were placed in the other. Inmates age 15 or younger were considered ineligible for the NIS-3.

The number of adult 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 10 percent chance among participating inmates of not receiving the sexual victimization questionnaire.
• an adjustment factor of 1.9 to account for the complex survey design;
• the size of the facility.

Each eligible adult 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 74,655 adult and juvenile prison inmates were selected. After selection, 2,233 ineligible inmates were excluded--1,441 (1.9 percent) were released or transferred to another facility before interviewing began, 657 (0.9 percent) were mentally or physically unable to be interviewed, 10 (0.01 percent) were age 15 or younger or their age could not be obtained during the interview process, 56 (0.5 percent) were selected in error (i.e., an inmate was incorrectly listed on the facility roster), 21 (0.03 percent) were only in the facility on weekends, and 47 (0.06 percent) were on unsupervised work release or only served time on weekends.

Of all selected eligible adult and juvenile prison inmates, 32 percent refused to participate in the survey, 0.5 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 0.5 percent were not interviewed due to survey logistics (e.g., language barriers, releases, or transfers to another facility after interviewing began).

Overall, 43,721 adult and juvenile prison inmates participated in the survey, yielding a response rate of 60 percent. Approximately 90 percent of the participating inmates (38,778) received the sexual assault survey. Among adult prison inmates, 38,251 inmates responded to the sexual assault survey.

Part III (Local Jails and State Prisons - Juveniles)

Selection of facilities

The NIS-3 was designed to oversample for facilities that house juveniles and to oversample juveniles within selected facilities. The resulting sample was structured to provide separate nationwide estimates for juveniles in prisons and jails, while providing national-level and facility-level estimates for adult inmates that were comparable to estimates in the NIS-1 and NIS-2.

Selection of juvenile inmates within jails

The number of inmates ages 16 to 17 sampled in each facility varied based on the number who appeared on the roster:

• If fewer than 50 were on the roster, all inmates ages 16 to 17 were selected
• If between 50 and 149 were on the roster, 75 percent were sampled (with a minimum of 50)
• If 150 or more were on the roster, 75 percent were sampled (with a minimum of 150)

In facilities in which not all inmates ages 16 to 17 were selected, each eligible inmate ages 16 to 17 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. As with adult jail inmates, a second roster obtained on the first day of data collection was used to identify inmates that had been arraigned since the initial roster was created or newly admitted. 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 1,211 juveniles in local jails completed the sexual assault survey.

Selection of juvenile inmates within prisons

The number of inmates ages 16 to 17 sampled in each facility varied based on the number who appeared on the roster:

• If fewer than 50 were on the roster, all inmates ages 16 to 17 were selected
• If between 50 and 149 were on the roster, 75 percent were sampled (with a minimum of 50)
• If 150 or more were on the roster, 75 percent were sampled (with a minimum of 150)

In cases in which not all inmates ages 16 to 17 were selected, each eligible inmate ages 16 to 17 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 527 juveniles in state prisons completed the sexual assault survey.

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Part I: Inmates age 18 or older in local jails and in special confinement facilities (Indian country, and Immigration and Customs Enforcement facilities) in the United States.Part II: Inmates age 18 or older in state and federal adult confinement facilities (including military facilities). Part III: Inmates ages 16 to 17 held in state and federal adult confinement facilities (including military facilities and in local jails and special confinement facilities (Indian country, and Immigration and Customs Enforcement facilities) in the United States.

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2015-04-03

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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 age 18 or older and the total number of inmates ages 16 to 17 who were held in jails at midyear 2011 or in prison at yearend 2011. These ratios represented the estimated number of inmates by sex (from BJS's 2011 Annual Survey of Jails and 2011 National Prisoner Statistics) divided by the number of inmates by sex for adults and overall for juvenile inmates ages 16 to 17 in the NIS-3, after calibration for sampling and nonresponse. The national estimates for state prisons were 1,154,600 adult males, 83,400 adult females, and 1,700 juveniles ages 16 to 17; for federal prisons, 190,600 adult males and 13,200 adult females (there were no juveniles ages 16 to 17 in federal custody); and for jails (with an average daily population of six or more inmates), 628,620 adult males, 91,551 adult females, and 5,700 juveniles ages 16 to 17.

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.

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