The study looked at whether giving legal status to some undocumented immigrants makes more people come illegally. They focused on the 1986 Immigration Reform and Control Act, which gave amnesty to over three million undocumented immigrants. They found that the number of people caught trying to cross the U.S.-Mexico border illegally went down right after the law passed, but went back up when undocumented immigrants could apply for amnesty and in the years after. This means that the amnesty program didn't change the usual amount of illegal immigration from Mexico.