Violence spreads like a virus | Science News for Students

Violence spreads like a virus

Friends of violent teens are more likely to become violent themselves
Jan 23, 2017 — 7:10 am EST
teen violence

Teens who have violent friends are much more likely to become violent themselves, new data show.


Choose your friends wisely. Teens who don’t can wind up in violent situations. Having friends who get into fights nearly doubles a teen's chances of doing the same. And the spread of violence doesn't stop there. It moves through an individual’s social networks, spreading like a virus. That’s the finding of a new study by researchers at Ohio State University in Columbus.

“People learn aggression and violence the same way they learn other behaviors,” says Brad Bushman — “through direct experience and by observing others.”

Bushman is a psychologist. He studies the human mind. He worked on the new study with Ohio State political scientist Robert Bond. The pair used data from a long-term project called the National Longitudinal Study of Adolescent Health. This project is also known as Add Health. Three times over several years, researchers with Add Health interviewed 90,118 students from across the United States in grades 7 through 12. The interviews occurred at least one year apart.

Bond and Bushman focused on the first two sets of interviews, from the 1990s. At that time, the kids had still been in school. The researchers specifically looked at students who had at least one friend or sibling who had also been interviewed. They did that so they could probe any links between violence in social groups.

The scientists homed in on the answers to three questions. How often back then had the student been in a serious physical fight? Had the teen hurt someone badly enough that their victim had needed bandages or other medical care? And had the teen pulled a knife or gun on someone? The questions asked how often such events had happened during the year leading up to the interview. In the end, Bond and Bushman used 5,913 interviews that mentioned friends who were also in the study and 4,904 interviews that mentioned siblings.

Teens with friends who said during their own interviews that they had been in a serious fight were 48 percent more likely to get into one themselves. Having a sibling who had been in a fight similarly increased a teen's chances of getting into a fight — here, by 38 percent. Teens with friends who had hurt someone badly enough to need medical attention were almost twice as likely to hurt someone badly themselves. And those whose friends had pulled a knife or gun were 40 percent more likely to do the same.

Those findings are staggering enough. But they're just the start.

Not only were a violent teen's close friends at high risk of showing violence. To understand how violence spreads within social groups, the researchers used a type of statistical method called network analysis. It allowed them to probe whether incidents of violence cluster together. That network analysis showed that when teens got into fights, violence increased among their friends’ friends, and in the friends of those people too — up to four people away from the original teen.

Bond and Bushman's results were published in the February American Journal of Public Health.

Violence almost appears contagious

The researchers liken the spread of violence to infections. “Like other contagious diseases, one can prevent and treat violence,” Bushman notes. “Prevention comes in the form of avoiding exposure to violence.” The best way to treat the disease is to teach teens to use non-violent methods to resolve conflict. He suggests that teens who struggle with violence should learn how to negotiate and try to compromise.

Violence is typically not dealt with as a health issue. But this study takes a different approach to people and their problems, says Gary Slutkin, who was not involved with new study. Slutkin works at the University of Illinois in Chicago. There, he’s an epidemiologist, someone who typically studies the spread of disease. Slutkin’s work focuses on violence as a public health problem.

Slutkin agrees that “violence is a contagious disease.” It's a health problem that has been misdiagnosed, he says. “It is important to understand problems,” he says and to “not judge people.”

Violence isn't the only type of behavior that spreads through social networks, adds Bushman. Positive behaviors, such as cooperation, sharing and helping others can be contagious, too. So the next time a friend asks you to pitch in and help out, jump at the opportunity to spread a healthy contagion.

Power Words

(more about Power Words)

behavior    The way a person or other organism acts towards others, or conducts itself.

bullying    (v. to bully) A group of repeated behaviors that are mean-spirited. They can include teasing, spreading rumors about someone, saying hurtful things to someone and intentionally leaving someone out of groups or activities. Sometimes bullying can include attacks using violence (such as hitting), threats of violence, yelling at someone or abusing someone with violent language. Much bullying takes place in person. But it also may occur online, through emails or via text messages. Newer examples including making fake profiles of people on websites or posting embarrassing photos or videos on social media.

contagion     (adj. contagious) A disease that can be spread by direct contact with an infected individual or the germs they spread into the air, their clothes or their environment. Such diseases are referred to as contagious.

epidemiologist   Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

infectious     An adjective that describes a type of germ that can be transmitted to people, animals or other living things.

National Longitudinal Study of Adolescent Health     Also known as Add Health. This long-term project that tracks the health of a nationally representative sample of U.S. adolescents who were in one of the grades 7 through 12 during the 1994-95 school year. This group of former students has been followed into young adulthood with four in-home interviews, the most recent in 2008. At that time, participants were aged 24 to 32. Another round of interviews were started in 2016 (and due to finish in 2018).

psychology    (adj. psychological) The study of the human mind, especially in relation to actions and behavior. To do this, some perform research using animals. Scientists and mental-health professionals who work in this field are known as psychologists.

sibling     An offspring that shares the same parents (with its brother or sister).

social   (adj.) Relating to gatherings of people; a term for animals (or people) that prefer to exist in groups. (noun) A gathering of people, for instance those who belong to a club or other organization, for the purpose of enjoying each other’s company.

social network    Communities of people (or animals) that are interrelated owing to the way they relate to each other. In humans, this can involve sharing details of their life and interests on Twitter or Facebook, or perhaps belonging to the same sports team, religious group or school.

virus   Tiny infectious particle consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.


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Journal: R.M. Bond & B. J. Bushman. The contagious spread of violence among US adolescents through social networks. American Journal of Public Health. Vol. 107, February 2017, p. 288. doi: 10.2105/AJPH.2016.303550.