“A few years ago, a pair of sociologists named Andrew Papachristos and Christopher Wildeman decided to study gun violence in Chicago. They focused on a specific community on the west side: overwhelmingly black and disproportionately poor, with a murder rate that was five times higher than the rest of the city.
“Their approach was to look at gun violence the way epidemiologists study disease — examining the way it spread by social connections. And like a virus, they found that there were certain people who were especially at risk of being touched by it.”