Sociology, which is sometimes defined as the painful and tedious explication of the obvious, occasionally comes up with useful insights, or at least proof that some useful insights are true. That seems to be the case with a study by Yale sociologist Andrew Papachristos, published in the academic journal Social Science & Medicine, and featured in the Chicago Sun-Times.

It turns out that being arrested with someone else is the best predictor of who will get shot in Chicago. No, not by the police, as the Al Sharptons of the world would like to claim. Shot by another civilian, in the epidemic of shootings that have made Chicago at some times more dangerous than Baghdad.

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 logic is pretty simple: if you are the type of person who goes out and commits crimes with others, you are probably connected to people who commit crimes with some frequency.  And that puts you at risk of getting shot, because people who commit crimes sometimes shoot others who become inconvenient, or who just get in the way.

The study is done with social network analysis, studying who knows who and how they interact, and drawing up networks that reveal the clustering that results from various commonalities.

 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.

These statistics demonstrate the wisdom of the old adage, “Lie down with dogs, wake up with fleas.” They also show that it is not per se that is related to the higher incidence of violence in some black communities…

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 rather the existence of networks of people who engage in violence and reinforce each other in patters of violent behavior.

There are some useful implications for policing in Chicago IF the race demagogues don’t start calling it profiling:

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.

Many other studies of crime have discovered that a relatively small group of people account for a very large share of the crime. Unfortunately, there are those who specialize in making it difficult for police to concentrate their resources where they are most needed. We’ll see what happens to Professor Papachristos and those who attempt to apply his insights.