Teens are 48% more likely to get involved in a serious fight and 183% more likely to hurt someone badly enough to require medical attention if a friend had done so, say researchers from Ohio State University.
"Other studies have shown we are influenced by our friends, but no other study has looked at whether, or how far the behavior spreads," said co-author Brad J. Bushman, a professor of communication and psychology and researcher on aggression and violence.
Bushman explained that his co-author, Robert Bond, an expert on social networks, had a "dataset that included measures of serious aggressive behavior."
"He didn't know much about aggression and violence, and I didn't really know much about social networks," said Bushman, so they decided to work together to test the hypothesis that violence spreads like a contagious disease.
Testing a theory
They began with a nationally representative sample of 90,118 students from 142 schools, with an average age of nearly 16 years. They had all participated in the National Longitudinal Study of Adolescent Health.
From this large sample, Bushman and Bond focused on two sub-samples. One sample included 5,913 students who were connected to at least one other student through a friendship and another included 4,904 students who were connected to at least one sibling. The researchers looked more closely at these participants because they'd been selected for at-home interviews along with filling out the survey questions.
The interviewers assessed violent behavior by asking participants to report the number of times in the preceding 12 months they had been involved in a serious physical fight, they had hurt someone badly enough to need bandages or medical care, and they had pulled either a knife or gun on someone.
All the students were also asked to name five male and five female friends at their schools.
Waves of data were reported every 12 months, Bushman said, and he and Bond looked at the first two waves: the first occurring between 1994 and 1995, the second occurring in 1996.
Data from the first wave showed that 32% of participants had been involved in at least one serious fight, 14% had hurt someone badly, and more than 2% had pulled a knife or gun on someone. In the second wave, 20% of participants had been in at least one serious fight, 6% had hurt someone badly, and approximately 3% had pulled a knife or gun on someone.
Because the numbers were so different, the researchers analyzed each of the three items separately instead of combining them into one measure of violence.
Degrees of separation
"We found that for serious fights, a participant was 48% more likely to engage in a serious fight if their friend had, and it spread four degrees to their friend's friend's friend's friend," explained Bushman. "And they were 140% more likely to pull a weapon on someone if their friend had -- and that spread three degrees to their friend's friend's friend. And they were 183% more likely to hurt someone badly enough to need medical attention, and that spread two degrees to their friend's friend."
When the researchers looked only at teen boys, they found that for each additional friend who had seriously hurt someone, the likelihood of a participant doing the same increased by 82%. Similarly, they discovered participants' likelihood of seriously hurting someone increased by 78% when their siblings had done so.
The study provides valuable information, said Dr. Cathryn Galanter, child and adolescent psychiatrist based in Brooklyn, New York, and a member of American Academy of Child and Adolescent Psychiatry.
"I think it's evidence for something that we see clinically and we also see in our daily life -- that often times there is a contagion effect to violence in that for adolescents, having an association with somebody violent or being in a community where there's a lot of violence puts you at risk" for committing violence, said Galanter.
She noted that the researchers also analyzed the data by controlling for demographic factors and the association remained for hurting people badly -- but it didn't remain for fighting or using a weapon. Because the researchers did not specify which demographic factors they controlled for, Galanter wondered how much of teen violence "is the impact of having a peer who is violent or being in a community where there's a lot of violence."
The assessment of violence is based on interviews with the teens -- and this is a problem, said Frank Farley, a psychologist and professor at Temple University and a former president of the American Psychological Association. He said he wonders "how honestly people would answer a question" about whether they pulled a gun on another person or hurt someone badly.
The one issue the authors "admit they could not resolve is selection versus contagion -- that is, if you have a violent friend, does that cause violence in you? Or on the other hand, do you select friends who are violent?" said Farley. "This study doesn't sort that question out."
Regardless of flaws, Galanter said she found the study rich in public health implications.
An ounce of prevention is worth a pound of cure
"Those kids with friends who are violent, communities that are violent -- those are places where we might want to think about prevention programs, and programs that can really help educate and protect kids and prevent future violence," said Galanter.
According to Farley, the study, though flawed, still produces some very interesting data on first, second, third and fourth degree connections related to violence.
"That's worth knowing," said Farley. Even though the researchers did not prove violence is contagious, they gave evidence of an association and constructed "a social and psychological map" for violence.
Farley convened a November summit on violence in Washington DC, where 20 experts talked about theories of violence and possible solutions. Emotional contagion is a related concept, noted Farley.
"We've seen emotional contagion in flash mobs," he said, explaining that "a random group of people who converge on the spot, with no particular goal in mind" may become violent if one person sparks it by, say, pushing over a lamppost. "Social facilitation" is another term psychologists use when discussing the contagion of violence, he said.
Bushman believes his results will prove useful to many people.
"I think it's really important for parents and policy makers and politicians and others to know that these networks matter a lot in terms of transmitting violent behavior," said Bushman.
In the introduction, he and Bond wrote, "To understand how violence spreads, one must understand the underlying psychological mechanisms. One key mechanism is imitation... Peer pressure has been linked to a wide variety of adolescent behaviors, including delinquency and aggression. There is also a growing literature on the biological changes associated with exposure to violence."
"There are two ways to treat any contagious disease ... you can prevent it or you can treat it," said Bushman. He believes it might be possible to reduce exposure to violence in the first place.
Farley agreed, noting: "We need all the thinking we can come up with as to the causes and preventions of violence."