In the 1990s, Vincent Felitti and Robert Anda conducted a study on adverse childhood experiences. They asked 17,000 mostly white, mostly upscale patients enrolled in a Kaiser HMO to describe whether they had experienced any of 10 categories of childhood trauma. They asked them if they had been abused, if their parents had divorced, if family members had been incarcerated or declared mentally ill. Then they gave them what came to be known as ACE scores, depending on how many of the 10 experiences they had endured.

The link between childhood trauma and adult outcomes was striking. People with an ACE score of 4 were seven times more likely to be alcoholics as adults than people with an ACE score of 0. They were six times more likely to have had sex before age 15, twice as likely to be diagnosed with cancer, four times as likely to suffer emphysema. People with an ACE score above 6 were 30 times more likely to have attempted suicide.