From January through October 2016, data were collected through face-to-face interviews with prisoners using computer-assisted personal interviewing (CAPI). In a CAPI interview, interviewers read questions aloud and enter responses directly into a laptop computer, allowing skip patterns and other routing criteria to be implemented automatically. SPI interviews averaged approximately 50 minutes, including about 2 minutes for the consent process and 48 minutes to complete the survey. Interviews were conducted in English (94 percent) and Spanish (6 percent).
The 2016 SPI was a stratified two-stage sample design in which prisons were selected in the first stage and prisoners within sampled facilities were selected in the second stage. A total of 364 prisons (306 state and 58 federal) participated in the 2016 SPI out of 385 selected (324 state and 61 federal), which included 15 sampled prisons that were deemed ineligible. A total of 24,848 prisoners participated (20,064 state and 4,784 federal) in the 2016 SPI, based on a sample of 37,058 prisoners (30,348 state and 6,710 federal), which included 1,549 sampled prisoners who were deemed ineligible for the survey.
The SPI sample was selected from a universe of 2,001 unique prisons (1,808 state and 193 federal) that were either enumerated in the 2012 Census of State and Federal Correctional Facilities or had opened between the completion of the census and July 2014. The target population for the 2016 SPI was male and female prisoners age 18 or older who were held in a state prison or were serving a sentence to federal prison in the U.S. during 2016.
A total of 364 prisons (306 state and 58 federal) participated in the 2016 survey out of the 385 selected (32 state and 61 federal). The other 21 prisons were not included, either due to non-response or ineligibility. The first-stage participation rate (i.e., the response rate among selected prisons) was 98.4 percent: 98.1 percent for state prisons (all but 6 out of 312) and 100 percent for federal prisons.
A total of 24,848 prisoners participated (20,064 state and 4,784 federal) in the 2016 SPI based on a sample of 37,058 prisoners (30,348 state and 6,710 federal). The second-stage response (i.e., the response rate among selected prisoners) was 70.0 percent: 69.3 percent among state prisoners and 72.8 percent among federal prisoners.