How economic theory can help stop sexual assault

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Photo by Flickr user Chase Carter.

Photo by Flickr user Chase Carter.

Editor’s Note: Michael Chwe studies game theory — as he says, “the mathematical analysis of strategic thinking.” In particular, he’s interested in how game theory shapes everyday life, as well as what everyday life can teach us about game theory.

Last year on this page, he presented his book “Jane Austen: Game Theorist,” and followed that up with a post defending Austen’s contributions to economics.

The UCLA political science professor returns to Making Sen$e today to explain how principles from game theory, when applied to reporting technology and efforts to change campus culture, could help communities reduce the incidence of sexual assault.

— Simone Pathe, Making Sen$e Editor


Sexual assault is shockingly common. In a 2005 survey of over 5,000 undergraduate women at two U.S. universities, roughly 20 percent reported experiencing some form of sexual assault during college. In 2012, the U.S. Department of Defense estimated that 14,000 male and 12,000 female service members were sexually assaulted that year. These numbers are intolerable. But how do we move from outrage to action?

Two initiatives have real potential: a web reporting system and social norms marketing. Both draw from ideas in law, psychology, sociology and political science. But aspects of both initiatives also closely relate to ideas from economic theory. Economics these days is not just about prices and markets; you might be surprised at how varied and fruitful economics can be.

Project Callisto

The first initiative, Project Callisto, is a web-based system for sexual assault reporting. According to the National Institute of Justice, “Many experts believe that rape and other forms of sexual assault are among the most underreported crimes.” There are several reasons for this. Survivors of sexual assault are often unsure whether what they experienced is really assault. They often worry about not being believed and retaliation if they report. The reporting process itself can be confusing, difficult and traumatic.

Callisto tries to fix this. A survivor can upload and time-stamp evidence, including images, audio and testimony, without having to decide at the time whether to forward it to authorities. This way, evidence is preserved soon after the assault, even if action is not immediate. Callisto is currently being developed by the non-profit organization Sexual Health Innovations, based on the advice of over 40 survivors of sexual assault, and was recently the subject of a New York Times Upshot story.

Callisto allows a survivor to choose to have his or her evidence forwarded to authorities automatically once another person uploads evidence about the same assailant. This way, a survivor can upload evidence knowing that he or she will not be the only accuser. It also allows a person, even if unsure about reporting his or her own case, to supply information that can help another person’s case and prevent future assault.

An Incentive to Report

As the Upshot piece points out, by combining information, Callisto serves as an “information escrow,” an idea proposed by Ian Ayres and Cait Unkovic in a 2012 Michigan Law Review article. Ayres, a law professor at Yale and a member of Callisto’s advisory board, and Unkovic, a graduate student at Berkeley, find that information escrows have several advantages.

Often, as illustrated by the recent cases of Bill Cosby and Jian Ghomeshi, a survivor speaks up after others have identified the same assailant. Again, it can be very difficult to be the first accuser. Callisto removes this disincentive: you can upload to Callisto knowing that authorities will be contacted only if another person uploads evidence about the same assailant. Also, since Callisto allows each person to store his or her evidence independently, each person’s evidence is more credible if it is later found to share common features (such as the assailant’s specific tactics) with others. You can’t be called a “copycat” accuser if you uploaded evidence years earlier.

Ayres and Unkovic note that an information escrow is a “game-theoretic technique.” Game theory, often used in economics and other social sciences, uses mathematics to model people’s choices when they interact with others. One of game theory’s subtopics is called “mechanism design,” and the idea of an information escrow is an example of “mechanism design” logic. The key idea of mechanism design theory is that to get a person to reveal truthful information, he or she must have the incentive to do so; therefore, a decision-making procedure should be designed to give people an incentive to report.

This is exactly the logic behind information escrows: if people are reluctant to be the only accuser, or are reluctant to report inconclusive information, then we should design a system that ensures that a person will not be the sole accuser and that his or her information will be aggregated with the information of others.

The Theory of Public Goods

The historical origins of mechanism design theory in economics go back, roughly speaking, to the theory of public goods. For private goods like coffee, in which only I care about how much coffee I buy, markets do a pretty good job of allocating resources efficiently. But the situation is different for public goods, such as schools and roads and other public infrastructure.

How do we figure out whether a public good should be built? If you ask people if they want to contribute to building a new highway, none of them has the incentive to report his or her true demand. For example, even if I really want the new highway, the best thing for me personally would be to say that I won’t contribute because I don’t really want one, and let everyone else build the highway, which I can then drive on afterward.

One way to solve this problem is to make the highway a toll road, more like a private good. But many public goods, like unpolluted air, are not “excludable,” and you cannot prevent people from benefiting from them. Because it is difficult to find out whether people really want a public good, public goods are likely to not be allocated efficiently: everyone might really want a new highway but no one wants to say how much he or she wants it out of fear they’ll have to pay for it.

Economists have considered this question for decades: how do you give people an incentive to truthfully report their demand for a public good? John Ledyard and Ted Groves made notable contributions in the 1970s. But people soon began to realize that the same issues arise in many social situations, not just in public goods, and out of this came mechanism design theory. In 2007, Leo Hurwicz, Eric Maskin and Roger Myerson won the Nobel Prize in economics for their contributions to that theory.

Economists working on public goods probably did not think about stopping sexual assault, but the power of a good idea is in how people make it unexpectedly useful. So it is not unreasonable to trace the theory of public goods to mechanism design theory to information escrows to Project Callisto. This is an example of how economic theory, in the form of either mathematics or just commonsense reasoning, can have unexpected implications that potentially benefit many people.

Social Norms Marketing

The second initiative that I believe has real potential is social norms marketing. To explain social norms marketing and how it relates to economic theory, I will start with the economics. A basic concept in economics is “externality,” which is how one person’s action affects the welfare of others. Practicing my electric guitar at midnight has negative externalities if my neighbors are trying to sleep but positive externalities if they are also guitar fans who stay up late. Goods like fax machines are said to have “network externalities” because my fax machine becomes a lot more useful if lots of other people buy fax machines and thus form a network.

Or How Macs Became Popular

How should one advertise a good with positive externalities? One example is the introduction of the Apple Macintosh in 1984. When the Apple Macintosh was introduced, it was incompatible with existing personal computers, and hence a person was more likely to want a Macintosh if others bought them also. The more people bought Macs, the greater the positive externality to me as a Mac owner. Thus the Macintosh was introduced with a now-legendary commercial during the 1984 Super Bowl. That ad did not simply let people know about the Macintosh; it also let people know that many other people knew about the Macintosh because it ran on the most popular television program of the year.

To advertise a good with positive externalities, you need to create not only knowledge of the good, but what game theorists call “common knowledge.” An event or fact is common knowledge if everyone knows it, everyone knows that everyone knows it, everyone knows that everyone knows that everyone knows it, and so forth. In the United States, the Super Bowl broadcast is the best common knowledge generator, so one would expect goods with positive externalities to be advertised there. Indeed, the great majority of the commercials airing on the Super Bowl are goods consumed in groups, such as beer, soft drinks, snack food, and movies (you are more likely to want to see a movie if you think other people are going to see it), as well as “network” goods such as cellular telephone plans.

Changing Our Beliefs about What Other People Believe

What does this have to do with sexual assault? It turns out that a great deal of social behavior, even violent behavior, is socially regulated in the sense that whether a person does it depends on whether other people do it and condone it.

In a 1996 paper, political scientist Gerry Mackie, of the University of California San Diego, talks about binding the feet of young girls in China, which lasted for roughly 1,000 years. Footbinding was undeniably a violent act: it was painful and horrific, and it is estimated that 10 percent of girls died from the experience. It persisted because if other families believed that a woman marrying into their family should have bound feet, you would have to bind your daughter’s feet if you wanted her to get married and have a future.

“Social change occurred not by convincing individual families that footbinding was wrong, but by informing each family about other families.”

But footbinding in China ended very quickly. In Tingshien, the percentage of girls with bound feet went from 99 percent in 1889 to zero percent in 1919. A crucial tactic of anti-footbinding societies was to have its members publicly pledge to not bind their daughters’ feet and not allow their sons to marry women with bound feet. Taking this pledge was similar to buying a Mac in 1984. Just as each Mac owner provided positive externalities to every other Macintosh owner, each family who did not bind their daughter’s feet and took the pledge provided positive externalities (namely, marriage opportunities) to every other family who did not bind their daughter’s feet. Social change occurred not by convincing individual families that footbinding was wrong, but by informing each family about other families.

Mackie, drawing upon the work of economics Nobel laureate Thomas Schelling, calls footbinding a “coordination problem.” That means that each person’s decision is heavily influenced by the decisions of others. If every other family believes in the practice of footbinding, then your daughter would be disadvantaged if you did not bind her feet. But if enough other families reject footbinding, then you would want to reject it also.

Mackie finds that the practice of female genital cutting, which affects 3 million girls in Africa each year, is similar; if everyone else believes in the practice, then your daughter’s marriageability would be hurt if you did not believe in it, too. But if everyone else abandons it, then you would abandon it. Mackie observes that previous attempts to convince individual families to stop female genital cutting were not effective; what has worked is getting entire collections of villages (basically, all the communities among which young people intermarry) to coordinate and publicly abandon the practice.

These kinds of efforts, which have already done much to reduce violence against girls and women, are examples of social norms marketing. Social norms marketing tries to change a person’s behavior not by changing his personal beliefs or values but by changing his beliefs about other people’s beliefs. It works, social psychologist Elizabeth Levy Paluck, of Princeton, and Laurie Ball Cooper, of American University, explain, by sending the message not only that “women are worthy of respect” but also that “men in this community believe in treating women with respect.”

The Power of Fraternities

Still, one might object that sexual assault is different from footbinding or female genital cutting: presumably no one who engages in sexual assault does so because he or she thinks that other people are doing so. But a person committing a violent act often does think about the overall social environment, which includes whether people who find out about his or her act will understand it as a crime and report it.

Lundy Bancroft makes this point in his 2003 book on domestic violence, “Why Does He Do That?”:

While a man is on an abusive rampage, verbally or physically, his mind maintains awareness of a number of questions: ‘Am I doing something that other people could find out about, so it could make me look bad? Am I doing anything that could get me in legal trouble?’

For example, regardless of how individual members of a college fraternity feel about sexual assault, a fraternity, as a collective, can be a physical and social environment in which a perpetrator has greater confidence, because of fraternal loyalties, that surrounding people will not report him.

But the collectivity of a group such as a fraternity can work in a positive sense too, encouraging reporting and intervention. In a 2003 paper, Patricia Fabiano at Western Washington University (WWU) and her co-authors surveyed 618 WWU undergraduate students and found that a male student was significantly more likely to say that he would intervene in situations that could lead to sexual assault if he believed that other male students would intervene.

Again, it’s about who knows what and, more importantly, who knows who knows what. In partnership with the UNESCO office in Mexico, Eric Arias, a graduate student in political science at NYU, tested the effects of an audio soap opera in San Bartolome Quialana, a rural community in Oaxaca with a population of 2,470. The soap opera was written as part of a UN Joint Program to stop violence against women, and based on the research of Paluck and others, included lines like “the citizens of Quialana believe that beating women is wrong,” instead of just saying, “beating women is wrong.”

After the soap opera, residents were asked questions about violence against women. Arias found that when residents heard the soap opera via the community’s public loudspeaker or in a community meeting, their answers to questions about violence against women changed significantly. However, if a resident listened to the soap opera via a CD in his or her own home, it had no significant effect. In other words, if you heard the soap opera but did not know that anyone else heard it too, you were unaffected. The soap opera seemed to “work” not by changing individual minds, but by changing what each individual knew about others in the community.

This kind of social norms marketing has been applied to the problem of sexual assault on college campuses since the 1990s (see this 2011 paper by Christine Gidycz at Ohio University and co-authors), but it’s exciting to see how scholars from multiple disciplines have all come to similar ideas starting from different fields.

Who knew that economic ideas about public goods could end up helping survivors report sexual assault, via Project Callisto? Or that positive externality theory could help change campus culture? At a time when sexual assault on college campuses, the military, and society in general, has emerged as a pressing problem, it’s heartening to know that ideas from the social sciences, even economics, can help.

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