This paper studies the behavior of price discovery within a context of an agent based stock market, in which the twin assumptions, namely, rational expectations and the representative agents normally made in mainstream economics, are removed. In this model, traders stochastically update their forecasts by searching the business school whose evolution is driven by genetic programming. Via these agent based simulations, it is found that, except for some extreme cases, the mean prices generated from these artificial markets deviate from the homogeneous rational expectation equilibrium (HREE) prices no more than by 20%. This figure provides us a rough idea on how different we can possibly be when the twin assumptions are not taken. Furthermore, while the HREE price should be a deterministic constant in all of our simulations, the artificial price series generated exhibit quite wild fluctuation, which may be coined as the well-known excessive volatility in finance.
Keywords: Price Discovery, Homogeneous Rational Expectation Equilibrium, Genetic Programming, Agent-Based Computational Finance, Excessive Volatility
Motivation and IntroductionIt has been argued that standard asset pricing model based on the twin assumptions, the representative agent and rational expectations hypothesis, can only lead to uninteresting dynamics, which can be anything but the real world. For example, under very regular conditions, the market can end up with the wellknown zero-trade theorem (Tirole, 1982). While there are several possibilities to escape from this no-trade conundrum, recent studies based on agent-based computational finance (ABCF) indicate that we can have almost everything simply by giving up the twin assumptions 1 . Nonetheless, an important issue generally left unexploited is: under what circumstances and on what aspects, can we still regard the standard asset pricing model with its homogeneous rational expectation equilibrium (HREE) as a reasonable approximation to the dynamics generated by the ABCF methodology.In this paper, we shall start the analysis from the aspect of price discovery. We are asking how well the HREE price can predict the movement of the price dynamics generated by an agent-based stock market. Basically, we start from a standard asset pricing model (Grossman and Stiglitz, 1980) and use the HREE price as the reference. We then build an agent-based computational version of the standard asset pricing model and generate the price dynamics from there. The price series generated will further be compared with the HREE price.