"My colleague Samuel Bowles used to say that there are two types of economist: the Priest and the Engineer. The Priests live in their own little world and spin theories without any reference to the facts. The Engineers live in the real world, collect data, analyze time series, make predictions, give policy advice, and generally ignore all but the most basic economic theory. Certainly, the Engineers never give a thought to what the Priests are doing (they're usually separating hyperplanes, playing with Fredholm operators, or lost in Banach space). Not surprisingly, the microeconomics textbook used in all the best graduate departments around the world has more than a thousand pages stocked with axioms and theorems, but there is not one economic fact in the whole book."