Kinetic Exchange Models for Income and Wealth Distributions

Increasingly, a huge amount of statistics have been gathered which clearly indicates that income and wealth distributions in various countries or societies follow a robust pattern, close to the Gibbs distribution of energy in an ideal gas in equilibrium. However, it also deviates in the low income and more significantly for the high income ranges. Application of physics models provides illuminating ideas and understanding, complementing the observations.Comment: 15 pages, 20 eps figures, EPJ class; To be published as "Colloquium" in Eur Phys J

The effects of periodic and continuous market environments on the performance of trading agents

Simulation experiments are conducted on simple continuous double auction (CDA) markets based on the experimental economics work of Vernon Smith. CDA models within experimental economics usually consist of a sequence of discrete trading periods or “days”, with allocations of stock and currency replenished at the start of each day, a situation we call “periodic” replenishment. In our experiments we look at both periodic and continuous-replenishment versions of the CDA. In this we build on the work of Cliff and Preist (2001) with human subjects, but we replace human traders with Zero Intelligence Plus (ZIP) trading agents, a minimal algorithm that can produce equilibrating market behaviour in CDA models. Our results indicate that continuous-replenishment (CR) CDA markets are similar to conventional periodic CDA markets in their ability to show equilibration dynamics. Secondly we show that although both models produce the same behaviour of price formation, they are different playing fields, as periodic markets are more efficient over time than their continuous counterparts. We also find, however, that the volume of trade in periodic CDA markets is concentrated in the early period of each trading day, and the market is in this sense inefficient. We look at whether ZIP agents require different parameters for optimal behaviour in each market type, and find that this is indeed the case. Overall, our conclusions mirror earlier findings on the robustness of the CDA, but we stress that a CR-CDA marketplace equilibrates in a different way to a periodic one

Price Dynamics in an Exchange Economy

The pure exchange model is the foundation of the neoclassical theory of value, yet equilibrium predictions and models of price adjustment for this model remained untested prior to the experiment reported in this paper. With the exchange economy replicated several times, prices and allocations converge sharply to the competitive equilibrium in continuous double auction (CDA) trading. Convergence is evaluated by comparing the extent of price adjustment within each market replication (or trading period) to the extent of adjustment across trading periods: most observed price adjustment occurs within trading periods, so price adjustment data are evaluated with the Hahn process model (Hahn and Negishi [1962]), which is a disequilibrium model of within-period trades. Estimation demonstrates that the model is consistent with observed price paths within each period of the exchange economy. The model is augmented with an additional assumption – based on observations from this experiment – that the initial trade price in period t+1 is randomly drawn from the interval between the minimum and maximum trade prices in period t. The estimated within-period adjustment rule, combined with this across-period adjustment rule, generates price paths similar to data from an experiment session.Competitive equilibrium, disequilibrium dynamics, continuous double auction, experimental economics, exchange economy, Hahn process, neoclassical theory of value, tatonnement, unit root tests

Who to listen to: Exploiting information quality in a ZIP-agent Market

Market theory is often concerned only with centralised markets. In this paper, we consider a market that is distributed over a network, allowing us to characterise spatially (or temporally) segregated markets. The effect of this modification on the behaviour of a market populated by simple trading agents was examined. It was demonstrated that an agent’s ability to identify the optimum market price is positively correlated with its network connectivity. A better connected agent receives more information and, as a result, is better able to judge the market state. The ZIP trading agent algorithm is modified in light of this result. Simulations reveal that trading agents which take account of the quality of the information that they receive are better able to identify the optimum price within a market