Expertise in the academic world is based on ideas. They are the basis of hypotheses and theories that attempt to provide explanations for how particular phenomena work. But hypotheses and theories in economics cannot be established as definitively as in sciences such as physics. For one thing, economists cannot make a hypothesis and then do controlled experiments to determine whether or not the hypothesis is right. They are forced, instead, to rely on models, historical information, or cross-national evidence to suggest, not ascertain, a possible outcome or outcome. Furthermore, economists' ideological and political views make their theories inaccurate and distorted. As a result, economics expertise is characterized by significant explanatory failures, and models are useful under some conditions and not others. Unfortunately, bad models in economics keep coming back even when the evidence doesn't support the theory or proves them to be wrong. Even though they are undead, as Paul Krugman called them, they still influence policies, even though they are wrong. The history of economics is full of “undead” or “zombie” ideas proclaimed by experts. Let's see one. At the time of the Great Depression in the 1930s, classical economists argued, despite prolonged periods of unemployment, that market economies would automatically approach full employment, as businesses would hire any worker who wanted a job, as long as the His contribution to the firm's production was greater than his salary paid. For them, there was always adequate demand for the production of these additional workers because supply created its own demand. The self-correcting mechanism of market economies has led them to recommend that governments refrain from intervening in the middle of the paper…what you expect to happen in your study”, while a theory is a well-established principle that explains some aspects of the world. Cherry, Kendra, Introduction to Research Methods.” http://psychology.about.com/od/researchmethods/ss/expdesintro_2.htmhttp://www.nytimes.com/2014/03/31/opinion/krugman-jobs-and-skills-and-zombies.html. Paul Krugman, the Nobel Prize-winning economist, called them “zombie ideas,” that is, ideas that should have been killed by evidence, but refuse to die. Cassidy, John (April 2013)”, THE REINHART AND ROGOFF CONTROVERSY: A SUMMARY", http://www.newyorker.com/online/blogs/johncassidy/2013/04/the-rogoff-and-reinhart-controversy-a -summing-up.htmlHerndon, Thomas, (April 2013), “The Graduate Student Who Arrested Reinhart and Rogoff Explains Why They Are Fundamentally Wrong,” http://www.businessinsider.com/herndon-responds-to-reinhart- rogoff-2013-4.