The U.S. has multiple studies of the general population that can be used for population-level investigation of sexual assault, including forced intercourse. The National Research Council recently conducted a thorough review of the survey measurement of sexual assault, identifying many important strengths and weaknesses.(24) For example, they concluded that the U.S. National Crime Victimization Survey (NCVS) likely underestimates the prevalence of sexual assault because of the in-person administration of NCVS interviews (which reduces privacy), the use of a screening measure with little context, and the criminal behavior focus of that survey (24). By contrast, surveys conducted in modes that offer more privacy, place questions about sexual assault in a context of other relationship and sex-related questions, and are presented to respondents as measuring a broader range of experiences than crimes are likely to obtain more complete reports of sexual assault. The three survey data sources used accomplish each of these goals: more private modes, sexual assault is asked in the context of all relationship experiences, and the surveys do not focus on crime. As fully nationally representative data sources, the three surveys used represent all Americans independent of their socioeconomic status, race, ethnicity, language, nationality, sex, gender identity, sexual orientation, religion, geography, ability, age, or culture.
The NSFG was specifically designed to serve as the national source of statistics on sexual relationships, reproductive health, childbearing, and other related topics (2). It is an important data source for studying sexual assault because it features lifetime histories of sexual partnerships, pregnancies, sex, and reproductive health issues. It also uses audio-computer assisted self-interviewing (ACASI) to provide privacy and immediate response encryption while asking questions about sensitive reproductive health issues, such as forced intercourse. The NSFG offers a nationally-representative sample of persons aged 15-49, private measurement of experiences with forced intercourse outside of a criminal context, and response rates that generally exceed 70% (reducing potential nonresponse bias (25)). Specific wording used in the NSFG measures and a discussion of issues related to respondent interpretation of the questions were previously published (12).
We used publicly available NSFG data (2011-2017) to update the pre-pandemic trends in experiences of forced intercourse. Professional interviewers conducted face-to-face interviews with ACASI for some sensitive items (including forced intercourse) in a probability-based, nationally-representative, area-clustered sample. The NSFG data collection from 2011-2013 interviewed 10,416 respondents aged 15-44 (72.8% response rate), from 2013-2015 interviewed 10,210 respondents aged 15-44 (69.3% response rate), and from 2015-2017 interviewed 10,094 respondents aged 15-49 (65.3% response rate) (26). NSFG measures of forced intercourse are limited to those aged 18 and over. Weights constructed to account for the complex nature of the NSFG sample design, along with stratum and cluster codes for variance estimation, were used for our analysis. Note that the NCHS chose not to release forced intercourse measures in unrestricted public data for the NSFG 2017-2019, despite having done so previously.
The 2017 PSID-TAS[2] collected data from 2,526 males and females aged 18-28 (87% response rate). The PSID-TAS age restriction necessitated restricting the ages of other samples when comparing to these data. Data were collected by telephone from October 2017 to June 2018. The 2019 PSID-TAS2 introduced a web option for data collection in addition to telephone, which yielded interviews from 2,595 males and females between November 2019 and July 2020 (86% response rate). Both studies replicated the NSFG wording for measures of forced intercourse. Estimates in this analysis incorporated the cross-sectional weight that accounts for the original PSID selection probability, non-response, differential eligibility, and calibration to known features of the population of interest (27,28).
The AFHS[3] was designed to collect data from two national sample replicates, fielded from April 2020 through April 2022. The AFHS uses a mixed-mode web/mail protocol to screen a random address-based probability sample of U.S. households and identify eligible household members aged 18-49. One randomly selected eligible respondent within each household is invited to complete the study, which replicates the content of the NSFG. Both the screening questionnaire and the survey were designed to be completed online, but can also be completed by returning paper questionnaires through the mail; like the use of ACASI to measure forced intercourse in the NSFG, the use of these self-administered modes is expected to increase reporting of this type of sensitive experience (29). Estimates in this analysis focused on 1,914 respondents aged 18-49 who responded to questions on forced intercourse and 596 respondents aged 18-28 to match the PSID-TAS. These estimates incorporated the final survey weights, in addition to bootstrap replicate weights that correctly reflect the stratified sample design and account for all nonresponse adjustments and calibration adjustments applied to the sampling weights. Particularly important, no area cluster sampling was necessary for the AFHS, introducing cost and statistical efficiency relative to face-to-face approaches (23). One consequence of this efficiency is the ability to achieve reliable estimates with fewer interviews. All analyses were performed using appropriate SURVEY procedures in SAS (version 9.4). The code is available upon request.
Outcome Measures
Our binary indicator for ever being forced to have intercourse (1=Yes, 0=No) was derived from two questions. If the respondent indicated that first sex was not voluntary or if they reported ever being forced to have sex, they were coded as ever forced to have intercourse.[4]
Analytic Approach
We first generated descriptive estimates of the percentages of subgroups defined by age and gender ever experiencing forced intercourse in 2011-2017, and 2020-2022 among those aged 18-49 based on the NSFG and AFHS data sources. Next, we focused on younger Americans, adding the PSID-TAS data (2017 and 2019) and restricting the age range to match PSID-TAS (18-28). Finally, we estimated the association between the cumulative experience of college attendance and rates of ever experiencing forced intercourse, focusing on men and women aged 24-28. By these ages, many Americans with college experience have finished attending college. This approach allowed us to compare the cumulative experience of ever being forced to have intercourse across different levels of completed college experience. We used a dichotomous measure of college attendance—less than four years of college attendance vs. four or more years of college attendance—to maintain comparability across data sources.
Though we provide estimates across the full age ranges studied (18-49 and 18-28), we also provide estimates for narrower age-range subgroups (e.g., 20-24). This addition is important because narrower age groups differ substantially in exposure to the risk of ever being forced to have intercourse. Not only do more years of life increase the time of exposure, but different birth cohorts also live through different periods that may alter risks. For example, new risks created by social distancing during the pandemic may differ greatly by birth cohort. Thus, even within the analyses of those aged 18-28, we provide additional documentation of even narrower age groups, 18-23 and 24-28, because these cohorts differ in their exposures to risk.
[2] Data are publicly available.
[3] Data are being processed for public release. All procedures involving human subjects for the AFHS were approved by the University of Michigan Health Sciences and Behavioral Sciences IRB (HUM00167171).
[4] For males from PSID-TAS, only the forced male-female question is asked.