Introduction

Non-volitional sex (NVS) is increasingly recognized as a major public health problem affecting young people and having long-term negative health outcomes [1,2]. Male and female adolescents and young adults with a history of sexual violence are at higher risk of developing a broad spectrum of psychological problems like depression [3–6], post-traumatic stress disorder or pain-related symptoms [7,8]. Further, NVS during childhood and adolescence has been associated with later high-risk sexual behavior, drinking and drug use [9–11]. Victims of NVS are also vulnerable to acquiring sexually transmitted infections (STIs) and experiencing unwanted pregnancies [12–18].

Since NVS occurs without mutual consent and against one’s will, it is a violation of fundamental human rights [19]. High prevalences of NVS are reported in the general population across the full lifespan including the young [20–22]. In 2011, 243,800 US residents age 12 or older (rate of 0.9 per 1.000) were victims of rape or sexual assault in that year [21]. A large national probability survey in the UK (NATSAL-3) reported that among sexually experienced women and men between the ages of 16 and 29 years, 16.4% experienced that someone attempted NVS and 3.7% experienced actual (completed) NVS [23]. The proportions of young people who experience NVS vary worldwide and across studies [19]. However, the direct comparison of proportions and associated factors is seriously hampered by the lack of a uniformly used measurement or definition of NVS. The UK’s Sexual Offences Act 2003 divides NVS into (1) rape, which involves penetration of the vagina, anus or mouth by a penis, (2) assault by penetration, which involves penetration of the vagina or anus by a body part (other than penis) or another object, and (3) sexual assault, which involves sexual touching of any part of the body without consent [20].

NVS is generally more often reported by young women than by young men [23–26]. Yet, men and women who had same-sex sexual experiences report the highest rates of NVS [23,27]. Next to age and same-sex activities, a wide range of factors related to socio-demographics, behavior, and social network have been associated with NVS [1–27]. Nevertheless, there is limited comparative data on the NVS experiences and associated factors in young men who have sex with women (yMSW) or men (yMSM), and women who have sex with men (yWSM) or women (yWSW).

This study uses a large Dutch population sample to examine the frequency of NVS and its associated factors among young people with and without same-sex experiences aged 12 to 25 years. Previous studies focused on forced sexual intercourse and not included other types of NVS, or included one general question about sex against one’s will. This study assesses total NVS, NVS by six different practices and NVS by two well-defined categories (i.e., by penetration and assault) [20]. We further examine their association with a wide range of factors to reveal essential new information about the prevalence of NVS by different characteristics of participants. We hope this information will signal care providers, caregivers, and educators to the occurrence of NVS, thereby targeting their attention to this multi-faceted problem in young people.

Patients and Methods

Results

In total, 10,401 young people filled in the questionnaire. We excluded 691 (6.6%) of them because they had missing data on any of the six NVS questions. Those who were excluded were similar to those included in terms of sex, age, region of residence and experience with anal sex. However, they were more likely (p<0.01) to have a lower educational level (60.8% versus 46.7%), non-Western ethnicity (17.2% versus 12.1%), and to have reported having intercourse (68.6% versus 61.1%). Finally, we included 3,884 young men and 5,826 young women in further analyses (S1 Table). The majority of these participants were of Western nationality and nearly half of them had a lower educational level. About two thirds of them were sexually experienced of whom about one in 10 young men or women ever had had a same sex experience.

Perpetrators of NVS

Of all the sexually experienced participants who reported experiencing NVS, 93.9% filled in the question about the most recent NVS perpetrator. In most instances of NVS by penetration (88.5%) or NVS by assault (72.5%), the perpetrator was known to the victim as an intimate partner, family member, good friend, or another acquaintance; no notable differences by sex or sexual orientation were observed (Fig 1). NVS by penetration was sometimes also reported to be violent, i.e. in 32.4% for yWSM, 22.2% for yMSW, 20.0% for yMSM and 54.4% for yWSW (p<0.01 compared to all other groups).

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Fig 1. Perpetrator of NVS by assault and NVS by penetration in most recent occurrence.

https://doi.org/10.1371/journal.pone.0132847.g001

Discussion

This study is the first population-based sample to assess the prevalence and associated factors of different types of NVS practices and to compare them between young people who do and do not report same-sex activities. NVS is common among adolescents and young adults in the Netherlands: 1 in 2 women and 1 in 4 men who are sexually experienced and between 12 and 25 years of age reported having experienced some form of NVS. Various types of NVS were observed; the prevalences ranged from 1% to 61%. NVS by penetration was reported by 1 in 5 young women and by 1 in 20 young men. Nearly all NVS types occurred more frequently among women and men with same-sex experiences.

This study provides a comprehensive overview of NVS in young people, revealing its different practices for the first time. It shows that NVS goes beyond the strict definition of rape or coercion. While violence was involved in about 1 in 2 to 5 cases of NVS by penetration, all types of NVS represent a violation of sexual autonomy and are therefore a more subtle form of sexual violence [28]. Corroborating earlier findings, the perpetrator is usually known to the victim [5, 23, 24]. Prevalence of any NVS in our study was higher than reported in a UK population sample, which asked single questions about “attempted and completed sex against your will” [23]. This disparity is likely due to differences in the questions asked. The prevalence found in the UK study was more in line with our findings about NVS by penetration.

Corroborating earlier findings [23–27], yWSW and yMSM experienced the highest proportions of NVS, followed by yWSM. Young people with same-sex experiences were found to be more vulnerable to NVS, but also to interpersonal violence and victimization in teen dating experiences [29]. Overall, risky behaviors that are associated with adverse health outcomes were associated with experiencing NVS. For example, young people reporting NVS were more likely to report a range of risky sexual and drug use behaviors [1–18,23–26] or to engage in internet-related sexual activities [29–31]. Other associated factors were also observed: these included a lower educational level, having sexual problems, a low self-efficacy for refusing sex [2], discussing issues with friends [32], and (for young men) reporting that among their friends it was the norm to have sex. Young women and men, who had experienced NVS themselves were the most likely to have forced someone else into NVS [33,34]. The associated factors for women and men appeared to be quite similar. We also observed only few to no differences in associated factors for NVS between yMSW and yMSM, and between yWSM and yWSW. Overall, more factors were associated, and often more strongly, with NVS by penetration than with NVS by assault. Thereby, for all four groups, a multifaceted range of associated factors has been revealed that can serve as signals to target sexual health care and NVS prevention.

We recognize several limitations of this study. Due to its cross-sectional design, the study precludes drawing any causal inferences about the associations observed. Moreover, the power to detect differences between young people with and without same-sex activities may have been reduced since there were fewer yMSM and yWSW in our sample. The prevalence of NVS may have been underreported due to possible recall bias or when young people not fully disclose such information as it may be too sensitive or not fully captured in the framing of the questions [35]. There may be some age related bias in the answers to the questions due to possible age-related interpretation of the questions. Still, we do not consider it very likely that such bias would be substantial as all the questions included the terminologies used by Dutch youth and were explained in detail in the questionnaire. Although the study included a large, relatively representative sample, we do acknowledge the possibility of a partly selected sample e.g. among the young people who did obtain consent from their caregivers (versus those who did not) to participate in the study. Finally, since some of the data was collected from participants who completed the questionnaire during classes at their schools, we cannot completely rule out the possibility of group pressure to give socially desirable answers. However, most students had their own computer work spaces.

Conclusion

This study reports on young people who have a high lifetime prevalence of NVS and for whom early intervention is essential and possible. NVS, whether by assault or penetration, was associated with a wide range of factors, corroborating previous reports and highlighting the highly clustered nature of factors associated with NVS and adverse sexual health outcomes in general [36]. NVS thus should be dealt with by interventions that address the multifaceted risk profile and that integrate existing care and prevention services.

The multifaceted risk profile, as revealed here, includes a lower educational level and a range of risky behaviours, i.e. related to sexual activity, drug use, and internet, STI test history, feeling unattractive, unsatisfied with own sexual life (women only), having sexual problems, having feelings of low self-efficacy to refuse sex (yMSM only), stating that the norm among friends to have sex (men only), and talking with friends about NVS. When these factors are encountered (either single or in combination) by educators, caregivers, and medical professionals dealing with young people, it should alert them to screen for NVS. In screening for NVS, we need to acknowledge the importance of asking about the different types of NVS experiences. Yet, in practice it may not be easy to address NVS either directly or indirectly, by its associated factors, due to the sensitive nature of these topics. Youth who have NVS experiences may not typically disclose them [23]. There is a growing understanding of NVS intervention strategies that may be useful in various settings (e.g., in communities and schools [37], using the internet or in clinical settings [36]). However, much remains to be understood about the specific social context that links NVS to the interventions and about the interventions that are most effective [36,37]. For example, the mainly heteronormative clinical and school environments may exacerbate health inequities for young people who engage in same-sex sexual activities [36,38]. To address NVS effectively and with integrated services, we urgently need carefully designed evidenced based interventions. The associated factors revealed in our current study can be an important starting point for systematic development of such interventions (e.g. by using intervention mapping [39]) including their successful implementation in educational, prevention and clinical contexts.

Supporting Information

Acknowledgments

We thank Ms. Anne-Marie Niekamp (Public Health Service South Limburg) for involvement in the data collection and Ms. Jeanne Heil for assistance with data weighting procedures. The authors would like to thank the team that facilitated the Dutch national survey ‘Sex under the age of 25 II’ from Rutgers WPF and STI AIDS Netherlands. We are grateful to all participants in this study.

Preliminary results of data presented in this paper has been presented as a poster at ISSTDR, Vienna, Austria, July 15, 2013. Sex Transm Infect 2013;89:Suppl 1 A308-A309 doi:10.1136/sextrans-2013-051184.0963 P4.065