Outcomes of interest

We estimated the incidence of self-reported exposure to various forms of violence in the last 12 months across two-year age bands for males and females in each country. We included violence types available in all five countries: physical violence perpetrated by a parent or adult caregiver, physical violence perpetrated by an adult in the community, physical or sexual intimate partner violence (IPV), and sexual violence (by any perpetrator). Questions on IPV are not included in Haiti’s questionnaire, so no estimates for IPV are presented for that country. Exposure to each type of violence is operationalized as a dichotomous variable signifying whether the respondent experienced each type of violence within the last 12 months. Specific questions used to construct these dichotomous variables vary slightly by country and can be found in each country’s VACS questionnaire (available upon request).

Analysis

Analyses were conducted separately for each country in the sample. We first estimated the incidence of each type of violence for males and females, separately. Differences between sexes were assessed using adjusted Wald tests. We then estimated the incidence of each type of violence for males and females, separately, across six two-year age bands: 13–14, 15–16, 17–18, 19–20, 21–22, and 23–24 years old. Two-year age bands were used to ensure age effects were as specific as possible and sample sizes were large enough to be sufficiently powered.

We assessed whether there are age effects for each type of violence exposure for males and females. A variable containing information on each individual’s two-year age-band was included as a continuous effect in a logistic regression estimating violence exposure in the last year. After testing for age effects for males and females, separately, we added sex to the model as an interaction term. Sex differences in age effects were assessed using adjusted Wald tests. All observations were weighted to be reflective of the larger population for each country and standard errors are adjusted for clustering and stratification in the sampling design. All analyses were conducted using Stata14.

Physical violence by an adult caregiver

Regression analysis revealed that males and females were less likely to experience physical violence by caregivers as they aged in all five countries (see Table 2). While this pattern was consistent across all contexts studied, the relative decline in risk by age differed by sex in Haiti. In Haiti, while results indicated that risk of physical violence by a parent or other caregiver declined for both males and females as they aged, this decline in risk was stronger for males (F = 5·21, p<0·05).

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Table 2. Sex and age effects for past-year exposure to violence.

https://doi.org/10.1371/journal.pone.0219073.t002

Physical violence by an adult community member

Similar age effects were observed for exposure to physical violence by a community member. For both males and females, the risk of experiencing this form of violence decreased with age in all countries in the sample. However, in Kenya, the odds of experiencing physical violence by an adult in the community decreased with age significantly more for males than for females (F-statistic = 10·99, p<0·01).

Intimate partner violence

In contrast to findings pertaining to physical violence, analysis revealed that risk of IPV increased with age for both males and females in all contexts reviewed (Cambodia, Kenya, Malawi, Tanzania). The levels of risk experienced were significantly higher for females in almost every context. This pattern was particularly pronounced in some countries. Additionally, in Malawi, females experienced a significantly greater increase in risk of IPV with age than did males (F = 4.21, p<0.05). For some countries, the highest prevalence of IPV appears to be at ages 17–18 or 18–19, followed by slight decreases.

Sexual violence

As stated above, females were victimized at higher rates than males in every country in the sample (Table 1). Further, risk of sexual violence also increased with age in many countries in our sample, with different patterns across countries and for females and males. In Kenya and Tanzania, analyses revealed an increasing risk of sexual violence with age for males (Kenya OR = 1.332, p<0.01; Tanzania OR = 1.181, p<0.05), but not for females. The same was true in Cambodia (OR = 1.475, p<0.001), although sexual violence in this context was relatively low for all age bands. In Haiti, however, the odds of experiencing sexual violence increased with age to similar degrees for males and females (F-statistic = 0.79). The prevalence of sexual violence appears to be highest in some countries at ages 17–18 or 18–19, followed by slight decreases.

Tailoring strategies for prevention and starting early

In order to mitigate the negative effects of violence and prevent early exposure, country-, age-, and sex- specific data can offer an important starting point. Identification of groups vulnerable to violence in early adolescence allows stakeholders to effectively target upstream solutions, such as primary–and even secondary and tertiary—prevention programs for younger populations of children. Given the fact that previous research shows that more than 50% of children as young as 2–14 years old have experienced any form of violence in the past year, there is a clear need to target such programs as early in the lifespan as is feasible [30]. A Canadian school-based violence prevention program focused on healthy relationship skills in early adolescence, for example, demonstrated a positive effect on reduction of physical IPV at a 2·5-year follow-up [31]. Similarly, school-based programs focused on improving social and emotional learning faculties amongst elementary school students have demonstrated longitudinal effects on reduction of aggressive attitudes and behavior [32].

The age-, sex- and country-level differences observed in the present analysis highlight why prevention efforts should be altered to more effectively address the specific risks faced by adolescents and young adults. For example, our findings suggest that corporal punishment may be disproportionately affecting boys in some countries, particularly in the early years of adolescence. This finding has been echoed in other recent studies that have found that, where gender differences are observed in experiences of corporal punishment, boys are more likely to report experiencing physical abuse from a parent than are girls [33]. Some parenting programs that target a reduction in physical violence against children and adolescents have been shown to be successful, but strategies may need to be adapted to different phases of child development to maximize impact. For example, the ACT Raising Safe Kids and Parents/Families Matter! programs, which have been implemented in several LMICs and have been shown to be effective in reducing harsh parenting practices for parents of younger children and adolescents, might need to be tailored to demonstrate the same impact for adolescents over 12 years of age [34, 35]. The REAL Fathers program, by incorporating a gender lens and targeting young fathers ages 16–25, has achieved success in preventing both participants’ use of IPV against female partners and physical violence against their 1–3 year-old children. However, the REAL Fathers program has yet to be tested with fathers of older children, where a different type of gender lens may need to be applied to account for gender differences in corporal punishment victimization [36]. Programs should usefully look across phases of child development and gender to understand and address how parenting practices differ for boys and girls across the child life span.

In addition to considering programming that is responsive to age and sex differences, it is important to acknowledge local context in such interventions [37]. The West African NGO Tostan recognizes the value of such local adaptation and has successfully leveraged this approach to reduce harmful practices against girls in the region. Specifically, an evaluation of their Community Education Program, which tailors program discussions around local constructions of human rights and harmful practices, found that 77% of graduated communities had permanently eradicated the practice of female genital mutilation a decade after program participation [38]. SASA!, a community mobilization intervention aimed at reducing gender-based inequality and violence in Uganda, also draws heavily on local conceptions of power and inequality; rather than implementing predetermined intervention activities, the program utilizes a bottom-up approach to respond to the specific needs and realities of each community [39]. As a result, evaluations of SASA! suggest that the program not only led to a decline in violence against women, but also reduced children’s exposure to corporal punishment and even led some community members to intervene in potential cases of child abuse [40]. In 2016, key global partners released INSPIRE, a technical package of evidence-based interventions to prevent and respond to violence against children. While INSPIRE has huge potential for policy and advocacy efforts, there is some risk that such a top down approach may privilege interventions shown to be effective in one context, possibly overshadowing effective community-based approaches that are yet unevaluated by large-scale RCTs.

Deepening our understanding: A need for data on norms alongside information on incidence

Collecting data on descriptive and injunctive norms surrounding violence, alongside data on experiences of violence, may be critical for the development of effective programming. Research on injunctive norms in other contexts has helped to illuminate how harmful norms exacerbate females’ experiences of violence [41]. In particular, data on injunctive norms can help shed light on instances where certain types of violence are especially elevated, normalized, and even accepted for a certain age group or sex. Research on dating violence perpetration in other contexts has found that injunctive norms surrounding acceptability of dating violence and gender role attitudes work synergistically to increase the likelihood of IPV perpetration amongst males [42]. Information on norms surrounding specific types of violence can help to clarify whether and why individuals consider use of that type of violence against a specific age group or sex to be acceptable. Together, data on norms and experiences can contribute to the design of more effective programs, particularly those engaging the broader community.

Recognizing the multiple roles boys and men hold

Data on violence exposure for 18–24 year olds in the VACS has been largely unexplored. Most analyses of VACS data have focused on childhood violence (before age 18), with data from ages 18–24 used to assess later impacts of childhood violence on health, wellbeing and behavior, and currently-held gender attitudes and norms [15, 43–44]. The analyses in this paper represent the first detailed examination of reports of past-year violence among older adolescents and young adults, and reveal important trends. This analysis may be particularly important in the work to engage men and boys in ending violence, recognizing that they hold multiple identities: survivors of violence themselves, potential champions of change, and the most likely perpetrators of violence against women and girls [15]. Despite growing evidence that violence in childhood (both witnessing and experiencing) is linked to males’ increased risk of perpetration of IPV and non-partner sexual violence later in life, the experiences of young males, particularly young adult males, with violence are often unknown [45–47]. This population may be left out of data on violence against children (which stops at age 18) and gender-based violence data (which primarily focuses on the victimization experiences of women). As research, programs, and policies are developed to better address the interlinkages of violence against children and violence against women, it is increasingly vital to create and use sex- and age-disaggregated lenses.

Limitations

Findings from this analysis should be considered alongside a few limitations. First, due to the self-reported nature of the outcomes of interest, it is possible that some participants were reluctant to disclose their violence experiences, thereby resulting in underestimations of exposures to different violence types. In order to minimize the likelihood of reporting bias for sensitive information, great care was taken to recruit, select, and train interviewers to build rapport and gain trust with participants. Second, the analysis presented here comprises multiple comparisons of violence risks. Given the ambiguous guidelines relating to which types of adjustments or Bonferroni corrections should be used for such complex comparisons, such adjustments were not made. Finally, due to small sample sizes the age effects may reflect spurious relationships; future research should explore these analyses with larger samples to confirm results.