Market economics has been widely used because of its efficiency (ability to work well). However, it has also been criticized for its selfishness and the difference between the rich and poor. In the real world, market economies are not purely market economies, as societies and governments control them in some ways instead of market forces. The expression "free-market economy" is sometimes used as the same as market economy. Nobel Prize in Economics winner Ludwig von Mises said that a market economy is still a market economy even if the government joins in pricing.