activity and with analysis beyond earlier institutional economics and neoclassical economics. It can be seen as a broadening step to include aspects excluded in neoclassical economics. It rediscovers aspects of classical political economy. Douglass North Oliver E. Williamson Ronald Coase Daron Acemoglu Steven N. S. Cheung 20th century schools Notable schools or trends of thought in economics in the 20th century were as follows. These were advocated by well-defined groups of academics that became widely known: Austrian School Biological economics Chicago School Constitutional economics Ecological economics Evolutionary economics Free-market anarchism Freiburg School Freiwirtschaft Georgism Institutional economics Keynesian economics Marxian (Marxist) and neo-Marxian economics Neo-Ricardianism New classical macroeconomics New Keynesian economics Post-Keynesian economics Public Choice school School of Lausanne Stockholm school In the late 20th century, areas of study that produced change in economic thinking were: risk-based (rather than price-based models), imperfect economic actors, and treating economics as a biological science (based on evolutionary norms rather than abstract exchange). The study of risk was influential, in viewing variations in price over time as more important than actual price. This applied particularly to financial economics, where risk/return tradeoffs were the crucial decisions to be made. An important area of growth was the study of information and decision. Examples of this school included the work of Joseph Stiglitz. Problems of asymmetric information and moral hazard, both based around information economics, profoundly affected modern economic dilemmas like executive stock options, insurance markets, and Third-World debt relief. Finally, there were a series of economic ideas rooted in the conception of economics as a branch of biology, including the idea that energy relationships, rather than price relationships, determine economic structure. The use of fractal geometry to create economic models (see Energy Economics). In its infancy the application of non-linear dynamics to economic theory, as well as the application of evolutionary psychology explored the processes of valuation and the persistence of non-equilibrium conditions. The most visible work was in the area of applying fractals to market analysis, particularly arbitrage (see Complexity economics). Another infant branch of economics was neuroeconomics. The latter combines neuroscience, economics, and psychology to study how we make choices. See also Birmingham School Buddhist economics Economic ideology History of economic thought Economic thought (category B) (JEL code) Kameralism Manchester School Structuralist economics Notes References Sources Spiegel, Henry William. 1991. The Growth of Economic Thought. Durham & London: Duke University Press. John Eatwell, Murray Milgate,