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 had 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.

For these families, the extra padding was a blessing, enough to boost household incomes by almost 20 percent on average. But for the fields of psychology, sociology and economics, it has been a gold mine, too. The sudden change in fortunes has offered a rare glimpse into the subtle but important ways in which money can alter a child’s life. The dataset is so rich that researchers continue to study it to this day.

Not only did the extra income appear to lower the instance of behavioral and emotional disorders among the children, but, perhaps even more important, it also boosted two key personality traits that tend to go hand in hand with long-term positive life outcomes.