Keynesian beauty contest

Keynesian beauty contest - Wikipedia, the free encyclopedia:

A Keynesian beauty contest is a concept developed by John Maynard Keynes and introduced in Chapter 12 of his work, General Theory of Employment Interest and Money (1936), to explain price fluctuations in equity markets. Keynes described the action of rational agents in a market using an analogy based on a fictional newspaper contest, in which entrants are asked to choose a set of six faces from photographs of women that are the 'most beautiful'. Those who picked the most popular face are then eligible for a prize.

A naïve strategy would be to choose the six faces that, in the opinion of the entrant, are the most beautiful. A more sophisticated contest entrant, wishing to maximize his chances of winning a prize, would think about what the majority perception of beauty is, and then make a selection based on some inference from his knowledge of public perceptions. This can be carried one step further to take into account the fact that other entrants would each have their own opinion of what public perceptions are. Thus the strategy can be extended to the next order, and the next, and so on, at each level attempting to predict the eventual outcome of the process based on the reasoning of other rational agents.

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Keynes believed that similar behavior was at work within the stock market. This would have people pricing shares not based on what they think their fundamental value is, but rather on what they think everyone else thinks their value is, or what everybody else would predict the average assessment of value is.

Other, more explicit scenarios help to convey the notion of the beauty contest as a convergence to Nash Equilibrium.