Twenty years ago, a group of researchers began tracking the personalities of 1,420 low income children in North Carolina. At the time, the goal was simple: to observe the mental conditions of kids living in rural America. But then a serendipitous thing happened.Four years into The Great Smoky Mountains Study of Youth, the families of roughly a quarter of the children saw a dramatic and unexpected increase in annual income. They were members of the Eastern Band of Cherokee Indians, and a casino has just been built on the reservation. From that point on every tribal citizen earned a share of the profits, meaning about an extra $4,000 a year per capita.