According to Levitt and Dubner, authors of the notable bestseller "Freakonomics", students have always had the reason to cheat - to get higher grades, which eventually prove to be a way to a better social standing. However, teachers also began to cheat, because now they also have an incentive to do it, because their jobs often depend on their students' success. A whole school in Chicago was on the verge of shutting down because of low grades, and teachers were caught cheating, so as to preserve their jobs. They cheated because they had an incentive. However, according to Levitt and Dubner's research, it's still the minority of teachers that will cheat (about 5%), whereas the majority of them is honest. The same goes for sumo wrestlers, who will often cheat because they aren't satisfied with the low wages most of them get.