A dynamic economy with shares, fiat, bank and accounting money

monetary models;monetary economics

An Informal Guide to Some Papers on a Theory of Money and Financial Institutions

The basic ideas behind a new approach to modeling money and financial institutions are summarized. A listing is given of a set of interrelated papers on this subject by the author, together with capsule summaries of each which can serve as a guide and introduction to the subject. Various unsolved problems and directions for further research are suggested. This paper was written to accompany a series of lectures given by Prof. Shubik at IIASA in April and May, 1977

Default and Punishment in General Equilibrium

We extend the standard model of general equilibrium with incomplete markets to allow for default and punishment. The equilibrating variables include expected delivery rates, along with the usual prices of assets and commodities. By reinterpreting the variables, our model encompasses a broad range of moral hazard, adverse selection, and signalling phenomena (including the Akerlof lemons model and Rothschild--Stiglitz insurance model) in a general equilibrium framework. We impose a condition on the expected delivery rates for untraded assets that is similar to the trembling hand refinements used in game theory. Despite earlier claims about the nonexistence of equilibrium with adverse selection, we show that equilibrium always exists, even with exclusivity constraints on asset sales, and transactions-liquidity costs or information-evaluation costs for asset trade. We show that more lenient punishment which encourages default may be Pareto improving because it allows for better risk spreading. We also show that default opens the door to a theory of endogenous assets.

Market Bubbles and Wasteful Avoidance: Tax and Regulatory Constraints on Short Sales

Although short sales make an important contribution to financial markets, this transaction faces legal constraints that do not govern long positions. In evaluating these constraints, other commentators, who are virtually all economists, have not focused rigorously enough on the precise contours of current law. Some short sale constraints are mischaracterized, while others are omitted entirely. Likewise, the existing literature neglects many strategies in which well advised investors circumvent these constraints; this avoidance may reduce the impact of short sale constraints on market prices, but may contribute to social waste in other ways. To fill these gaps in the literature, this paper offers a careful look at current law and draws three conclusions. First, short sales play a valuable role in the financial markets; while there may be plausible reasons to regulate short sales-- most notably, concerns about market manipulation and panics -- current law is very poorly tailored to these goals. Second, investor self-help can ease some of the harm from this poor tailoring, but at a cost. Third, relatively straightforward reforms can eliminate the need for self-help while accommodating legitimate regulatory goals. In making these points, we focus primarily on a burden that other commentators have neglected: profits from short sales generally are ineligible for the reduced tax rate on long-term capital gains, even if the short sale is in place for more than one year.Short sales, Momentum traders, Value investors

Some Dynamics of a Strategic Market Game with a Large Number of Agents

This paper is designed to combine the game theoretic investigation of the static or equilibrium properties of large strategic market games together with the investigation of some very simple dynamics, which nevertheless are sufficient to show differences between two related games, one in which both borrowing and trade take place. The role of banking reserves emerges as relevant and sensitive to the transient state dynamics. Several 100,000 player games are simulated and the behavior is constructed with the analytical prediction for the games with a continuum of agents

Price Variations in a Stock Market with Many Agents

Large variations in stock prices happen with sufficient frequency to raise doubts about existing models, which all fail to account for non-Gaussian statistics. We construct simple models of a stock market, and argue that the large variations may be due to a crowd effect, where agents imitate each other's behavior. The variations over different time scales can be related to each other in a systematic way, similar to the Levy stable distribution proposed by Mandelbrot to describe real market indices. In the simplest, least realistic case, exact results for the statistics of the variations are derived by mapping onto a model of diffusing and annihilating particles, which has been solved by quantum field theory methods. When the agents imitate each other and respond to recent market volatility, different scaling behavior is obtained. In this case the statistics of price variations is consistent with empirical observations. The interplay between "rational" traders whose behavior is derived from fundamental analysis of the stock, including dividends, and "noise traders," whose behavior is governed solely by studying the market dynamics, is investigated. When the relative number of rational traders is small, "bubbles" often occur, where the market price moves outside the range justified by fundamental market analysis. When the number of rational traders is large, the market price is generally locked within the price range they define.

Nash bargaining in ordinal environments

We analyze the implications of Nash’s (1950) axioms in ordinal bargaining environments; there, the scale invariance axiom needs to be strenghtened to take into account all order-preserving transformations of the agents’ utilities. This axiom, called ordinal invariance, is a very demanding one. For two-agents, it is violated by every strongly individually rational bargaining rule. In general, no ordinally invariant bargaining rule satisfies the other three axioms of Nash. Parallel to Roth (1977), we introduce a weaker independence of irrelevant alternatives axiom that we argue is better suited for ordinally invariant bargaining rules. We show that the three-agent Shapley-Shubik bargaining rule uniquely satisfies ordinal invariance, Pareto optimality, symmetry, and this weaker independence of irrelevant alternatives axiom. We also analyze the implications of other independence axioms