Congressional Research Services reports that over the past 25 years, college fees rose almost 2 percent faster than inflation every year. This suggests that college has become expensive relative to the cost of living. At the same time, a college education is increasingly valuable. College graduates earn more money and have better career prospects than those who only have a high school degree. In the U.S., three main sources of money give revenue to colleges. They are government appropriations, gift and endowment revenue, and payments for tuitions and fees. If one source of revenue decreases, colleges often look to raise revenue in another place. When students talk about the price of college, they are usually referring to payments for tuition and fees. Both public and private schools engage in price discrimination, which means charging different prices to different students. Adam Davidson, writing in the New York Times, says that the rise of college prices is a sign of market competition in elite colleges.