Professors at Yale University have roiled the immigration debate with a new study calculating there are between 16 million and 30 million illegal immigrants in the U.S. — as much as three times more than most demographers figure.

The professors’ model looked at estimates of how many people came illegally, and how many people likely left, and concluded there are a lot more people who arrived than the 11 million suggested by traditional estimates. The model says the most likely figure is double that, at about 22 million.