One in four men surveyed for a United Nations study in Asia and the Pacific admitted raping at least one woman.

The UN Multi-country Study on Men and Violence in Asia and the Pacific surveyed over 10,000 men at nine sites in six countries: Bangladesh, China, Cambodia, Indonesia, Papua New Guinea, and Sri Lanka. At the survey site in China, 23 percent of men admitted to at least one rape. In Papua New Guinea, that figure was 61 percent.

To understand what's behind such startling figures, National Geographic spoke with Rachel Jewkes, the lead technical adviser for the study.

You've studied rape extensively in South Africa and now across Asia and the Pacific. How did you get involved in this kind of research?

I moved out to South Africa from England in 1994. I had a job to set up the women's health research unit in the South African Medical Research Council. I was told that the key issues in women's health were things like teenage pregnancy, so I said, "Okay, I'm willing to do research on teenage pregnancy, but as part of this work I want to talk to teenagers about how they got pregnant." We interviewed 24 pregnant teenagers. Twenty-three out of the 24 told us stories about being raped. I had absolutely no idea that sexual violence was a phenomenon that could have this sort of prevalence.

What have you learned about why men rape?

Sexual entitlement is the most common motivation across all of these countries. I think that very, very strongly points to the root of rape in gender relations, and the fact that rape is really legitimized in so many of these countries.

What do you mean by sexual entitlement?

Sexual entitlement means feeling that you ought to be able to have sex with a woman—essentially, if you want it, you can have it. The flip side of that is [the idea] that it's a woman's responsibility to make sure that she doesn't have sex when she doesn't want it. If a woman is raped, she would be blamed for putting herself at risk for being raped.

How did you select the countries that you studied?

It certainly wasn't because we knew that rape or violence against women was more common in those countries. We wanted to get a range of different parts of Asia, so we wanted south Asia, southeast Asia, and east Asia as well as the Pacific. Then we wanted countries where we had a UN partner that would fund the study and was committed to using the results for developing prevention programming.

How did you get the men who were surveyed to participate, let alone answer the questions honestly?

Well, there were two things. The first is that we didn't say, "Look here, we're doing a survey on rape," because that would not have been a winning line. In most countries, this is a survey about family health and relationships, which is true because the questionnaire has a lot of health questions in it, and there were lots of relationship questions.

The second thing is that we used partial self-completion for this survey. Questions were administered by a field worker of the same sex as the person we were interviewing, but there was one schedule of questions for men that was self-completed. We did this because we felt that men would be much more happy about providing information about illegal activities—rape, gang involvement, drugs, homosexuality—if they didn't have to actually verbalize the answer to a fieldworker. We set it up using an app on an iPod touch.

Why is the incidence of rape so high in Papua New Guinea?

I think it's the confluence of a culture that is extremely patriarchal and a culture that is extremely accepting of the use of violence in a whole range of different circumstances. It's not just gender-based violence, but also very severe and frequent use of violence in childrearing, and a lot of fighting in the community between men.

Why is rape comparatively less common in other countries that you studied?

I think that they may be slightly more peaceable countries. The two countries that really spring to mind are Bangladesh and most of Indonesia. Alcohol use is much lower in Bangladesh and in Indonesia, too. They are both Muslim countries, they both have relatively strict social mores around sex, and one way or another child abuse is less common in those countries. Child abuse really is strongly associated with rape and violence later on.

Nearly 4 percent of the men surveyed said they had participated in gang rape. Are there differences between perpetrators of single rapes and gang rapes?

Gang rape is associated more with poverty. There's been quite interesting research to argue that men come together in gangs and then get involved in a whole range of violence and antisocial activities as a way of trying to assert their masculinity, to make themselves feel like strong and powerful men. The conditions of poverty that they live in prevent them from having access to more traditional manifestations of manhood, such as being a provider. Their energies get directed rather into demonstrating sexual success with women, demonstrating dominance and control over women, and fighting with other men.

What issues do public health officials immediately worry about when they see a high prevalence of rape?

A very high proportion of women who are raped develop mental health consequences. Some research suggests that nearly all of them develop some symptoms of post-traumatic stress disorder (PTSD) at some stage. PTSD is very debilitating because it severely interferes with social relationships. Mothers with PTSD are much less able to look after their children, and they're much less able to keep a job.

In circumstances where you see lots of non-partner sexual violence, you are also likely to see a lot of child abuse that needs to be addressed and lots of other violence used in other ways in the society. It really is a big job trying to program ways to reduce exposure to violence overall in society.

Do you think the process of answering the survey questions made the men who had raped reconsider their actions?

If you ask men if they made their wife have sex even if she didn't want it and they say yes, at the end of the interview you ask, "What was the most severe consequence? Did you get arrested? Did you get jailed?" At [that] point ... they sit up and say, "You mean, I've just told you I've done something I could get arrested or jailed for?" It certainly made them sit up and think. We actually know that that's the case from work in South Africa, because we've gone back and interviewed people after they've been asked questions.

What do you hope happens now as a result of this study?

I've got two hopes. The first is that there is a political commitment in the countries where we worked to develop a proper program of action for violence prevention and to actually implement it.

The second hope is that at a global level people sit up and think about violence perpetration in a different way. I would like to see us in a place where we say: Our goal is going to be to end violence against women. That would be an incredibly powerful development agenda. We know that violence against women is not only incredibly harmful to the individual women, but it [also] has an impact on women's involvement in the economy and education.

In order to end violence against women, we have to end violence against children. If we end violence against children, we have a huge impact on violence of all kinds perpetuated across the globe.