If you and another person get arrested together in Chicago, you’re both part of a loose network of people with a high risk of getting shot in the future, Yale University researchers say in a newly published study.

Only 6 percent of the people in Chicago between 2006 and 2012 were listed on arrest reports as co-offenders in crimes, the study says. But those people became the victims of 70 percent of the nonfatal shootings in the city over the same period.

The study, called “Tragic, but not random: The social contagion of nonfatal gunshot injuries,” was published in the January 2015 issue of Social Science & Medicine. It shows the risk of becoming a gunshot victim in Chicago is “more concentrated than previously thought,” according to Andrew Papachristos, one of the authors.

More than ever, the Chicago Police Department is borrowing ideas from academics like Papachristos to fashion anti-violence strategies. For instance, the department used his social-network theories to generate its own list of at-risk people.

Police Supt. Garry McCarthy believes that list is helping his beat officers concentrate on those people most likely to become shooting victims — or to shoot someone else.

According to the department, many became gun victims anyway: Since it was created in 2013, dozens of people on the list have been shot. But what can’t be measured is the violence the list might have prevented, department officials say. They say the list is part of the reason murders and nonfatal shootings were down in 2014 compared to 2012, the year before the list was created.

Papachristos — an associate professor of sociology at Yale and a former Chicagoan with an expertise in gangs — said his study found that exposure to gunshot victims also increases one’s odds of becoming a shooting victim.

And as was previously known, race was a key risk factor in getting shot, the study noted. For every 100,000 people, an average of one white person, 28 Hispanics and 113 blacks became victims of nonfatal shootings every year in Chicago over the six-year study period.

But Papachristos and his team sought to go beyond a racial explanation for nonfatal shootings. They were trying to explain why a specific young African-American male in a high-crime neighborhood becomes a shooting victim, while another young black man in the same neighborhood doesn’t, the study said.

Such social network analysis allows the manpower-strapped Chicago Police Department to “discern who’s at risk rather than casting the net really wide,” he said.

The latest Yale University study was built on Papachristos’ previous social-network research into murders on the West Side. He had studied killings between 2005 and 2010 in West Garfield Park and North Lawndale. About 70 percent of the killings occurred in what Papachristos found was a social network of only about 1,600 people — out of a population of about 80,000 in those neighborhoods. Inside that social network, the risk of being killed was 30 out of 1,000. For the others in those neighborhoods, the risk of getting murdered was less than one in 1,000.

Papachristos said his team has been doing similar social network research in Boston; Cincinnati; Newark; New Haven, Conn.; East Palo Alto, Calif.; Stockton, Calif.; and other cities.

“You are also seeing a clustering of victims in small networks there,” he said. “We’re seeing a pattern.”

The Chicago Police Department is employing social network strategy in several ways.

Since 2010, Chicago Police officials, prosecutors and community leaders have organized meetings with members of opposing gang factions after murders are committed in their neighborhoods. Many of those gang members called to the meetings are on parole or probation and are required to show up. According to the police department’s guidelines for such “call-ins”: “The general message conveyed is, ‘We will help you if you will let us, but we will stop you if you make us.’ There will be a clear message that the group will be dismantled if they do not comply.”

Papachristos said he’s getting ready to release a study on the effectiveness of call-ins in Chicago. He would not provide details, but said: “We are seeing a reduction in shootings that these groups [gang factions] are involved in. It seems to be working.”

In March 2013, meanwhile, the department devised its so-called “two degrees of separation” list modeled on Papachristos’ work. The department started with people who were killed between 2010 and 2012. People who were once arrested with those victims were placed on the list, along with people who were once arrested with those associates of the victims. About 100,000 people were on the original citywide list.

Then the department whittled the list to several hundred people at the highest risk of being killed. They included 73 people in the Grand Crossing District and 30 people in the South Chicago District. Every other district had no more than 20 people on the list.

Since March 2013, 40 of the 504 people on the list have been shot, three fatally. Another person was murdered in an incident that didn’t involve a gun, according to the department.

Beat officers have been urged to pay special attention to people on the list because they pose the greatest danger to the public and themselves, said Robert Tracy, chief of crime control strategy for the department. Whenever officers nab someone on the list, they are required to note “two degrees of separation” on the arrest report, he said.

“We’re keeping track of them,” Tracy said. “Arming our officers with more intelligence has helped us drive down crime.”

District commanders have even met personally with some on the list to give them “custom notifications” that they’re being watched and will get arrested if they step out of line. They’re also offered social services to get out of a life of crime.

“This is tough love,” Tracy said.