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On the Impossibility of Informationally Efficient Markets
TL;DR: In this paper, the authors propose a model in which there is an equilibrium degree of disequilibrium: prices reflect the information of informed individuals (arbitrageurs) but only partially, so that those who expend resources to obtain information do receive compensation.
Abstract: If competitive equilibrium is defined as a situation in which prices are such that all arbitrage profits are eliminated, is it possible that a competitive economy always be in equilibrium? Clearly not, for then those who arbitrage make no (private) return from their (privately) costly activity. Hence the assumptions that all markets, including that for information, are always in equilibrium and always perfectly arbitraged are inconsistent when arbitrage is costly. We propose here a model in which there is an equilibrium degree of disequilibrium: prices reflect the information of informed individuals (arbitrageurs) but only partially, so that those who expend resources to obtain information do receive compensation. How informative the price system is depends on the number of individuals who are informed; but the number of individuals who are informed is itself an endogenous variable in the model. The model is the simplest one in which prices perform a well-articulated role in conveying information from the informed to the uninformed. When informed individuals observe information that the return to a security is going to be high, they bid its price up, and conversely when they observe information that the return is going to be low. Thus the price system makes publicly available the information obtained by informed individuals to the uninformed. In general, however, it does this imperfectly; this is perhaps lucky, for were it to do it perfectly , an equilibrium would not exist. In the introduction, we shall discuss the general methodology and present some conjectures concerning certain properties of the equilibrium. The remaining analytic sections of the paper are devoted to analyzing in detail an important example of our general model, in which our conjectures concerning the nature of the equilibrium can be shown to be correct. We conclude with a discussion of the implications of our approach and results, with particular emphasis on the relationship of our results to the literature on "efficient capital markets."
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TL;DR: The authors argued that the preponderance of theoretical reasoning and empirical evidence suggests a positive first-order relationship between financial development and economic growth, and that financial development level is a good predictor of future rates of economic growth.
Abstract: The author argues that the preponderance of theoretical reasoning and empirical evidence suggests a positive first order relationship between financial development and economic growth. There is evidence that the financial development level is a good predictor of future rates of economic growth, capital accumulation, and technological change. Moreover, cross-country, case-style, industry level and firm-level analysis document extensive periods when financial development crucially affects the speed and pattern of economic development. The author explains what the financial system does and how it affects, and is affected by, economic growth. Theory suggests that financial instruments, markets and institutions arise to mitigate the effects of information and transaction costs. A growing literature shows that differences in how well financial systems reduce information and transaction costs influence savings rates, investment decisions, technological innovation, and long-run growth rates. A less developed theoretical literature shows how changes in economic activity can influence financial systems. The author advocates a functional approach to understanding the role of financial systems in economic growth. This approach focuses on the ties between growth and the quality of the functions provided by the financial systems. The author discourages a narrow focus on one financial instrument, or a particular institution. Instead, the author addresses the more comprehensive question: What is the relationship between financial structure and the functioning of the financial system?
5,967 citations
TL;DR: In this article, the authors present a simple overlapping generations model of an asset market in which irrational noise traders with erroneous stochastic beliefs both affect prices and earn higher expected returns.
Abstract: We present a simple overlapping generations model of an asset market in which irrational noise traders with erroneous stochastic beliefs both affect prices and earn higher expected returns. The unpredictability of noise traders' beliefs creates a risk in the price of the asset that deters rational arbitrageurs from aggressively betting against them. As a result, prices can diverge significantly from fundamental values even in the absence of fundamental risk. Moreover, bearing a disproportionate amount of risk that they themselves create enables noise traders to earn a higher expected return than rational investors do. The model sheds light on a number of financial anomalies, including the excess volatility of asset prices, the mean reversion of stock returns, the underpricing of closed-end mutual funds, and the Mehra-Prescott equity premium puzzle.
5,703 citations
TL;DR: A review of the market efficiency literature can be found in this article, where the authors discuss the work that they find most interesting, and offer their views on what we have learned from the research on market efficiency.
Abstract: SEQUELS ARE RARELY AS good as the originals, so I approach this review of the market efficiency literature with trepidation. The task is thornier than it was 20 years ago, when work on efficiency was rather new. The literature is now so large that a full review is impossible, and is not attempted here. Instead, I discuss the work that I find most interesting, and I offer my views on what we have learned from the research on market efficiency.
5,506 citations
TL;DR: For example, this paper found that men trade 45 percent more than women and earn annual risk-adjusted net returns that are 1.4 percent less than those earned by women, while women perform worse than men.
Abstract: Theoretical models of financial markets built on the assumption that some investors are overconfident yield one central prediction: overconfident investors will trade too much. We test this prediction by partitioning investors on the basis of a variable that provides a natural proxy for overconfidence--gender. Psychological research has established that men are more prone to overconfidence than women. Thus, models of investor overconfidence predict that men will trade more and perform worse than women. Using account data for over 35,000 households from a large discount brokerage firm, we analyze the common stock investments of men and women from February 1991 through January 1997. Consistent with the predictions of the overconfidence models, we document that men trade 45 percent more than women and earn annual risk-adjusted net returns that are 1.4 percent less than those earned by women. These differences are more pronounced between single men and single women; single men trade 67 percent more than single women and earn annual risk-adjusted net returns that are 2.3 percent less than those earned by single women.
3,803 citations
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TL;DR: This paper proposed a theory of securities market under- and overreactions based on two well-known psychological biases: investor overconfidence about the precision of private information; and biased self-attribution, which causes asymmetric shifts in investors' confidence as a function of their investment outcomes.
Abstract: We propose a theory of securities market under- and overreactions based on two well-known psychological biases: investor overconfidence about the precision of private information; and biased self-attribution, which causes asymmetric shifts in investors' confidence as a function of their investment outcomes. We show that overconfidence implies negative long-lag autocorrelations, excess volatility, and, when managerial actions are correlated with stock mispricing, public-event-based return predictability. Biased self-attribution adds positive short-lag autocorrelations (momentum), short-run earnings drift, but negative correlation between future returns and long-term past stock market and accounting performance. The theory also offers several untested implications and implications for corporate financial policy.
Prepublication version available at https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2017
3,303 citations
References
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TL;DR: Efficient Capital Markets: A Review of Theory and Empirical Work Author(s): Eugene Fama Source: The Journal of Finance, Vol. 25, No. 2, Papers and Proceedings of the Twenty-Eighth Annual Meeting of the American Finance Association New York, N.Y. December, 28-30, 1969 (May, 1970), pp. 383-417 as mentioned in this paper
Abstract: Efficient Capital Markets: A Review of Theory and Empirical Work Author(s): Eugene F. Fama Source: The Journal of Finance, Vol. 25, No. 2, Papers and Proceedings of the Twenty-Eighth Annual Meeting of the American Finance Association New York, N.Y. December, 28-30, 1969 (May, 1970), pp. 383-417 Published by: Blackwell Publishing for the American Finance Association Stable URL: http://www.jstor.org/stable/2325486 Accessed: 30/03/2010 21:28
18,295 citations
TL;DR: In this article, the authors provide a simple example of an economy in which equilibrium prices and quantities exhibit what may be the central feature of the modern business cycle: a systematic relation between the rate of change in nominal prices and the level of real output.
4,451 citations
TL;DR: Rao's Linear Statistical Inference and Its Applications as discussed by the authors is one of the earliest works in statistical inference in the literature and has been translated into six major languages of the world.
Abstract: "C. R. Rao would be found in almost any statistician's list of five outstanding workers in the world of Mathematical Statistics today. His book represents a comprehensive account of the main body of results that comprise modern statistical theory." -W. G. Cochran "[C. R. Rao is] one of the pioneers who laid the foundations of statistics which grew from ad hoc origins into a firmly grounded mathematical science." -B. Efrom Translated into six major languages of the world, C. R. Rao's Linear Statistical Inference and Its Applications is one of the foremost works in statistical inference in the literature. Incorporating the important developments in the subject that have taken place in the last three decades, this paperback reprint of his classic work on statistical inference remains highly applicable to statistical analysis. Presenting the theory and techniques of statistical inference in a logically integrated and practical form, it covers: * The algebra of vectors and matrices * Probability theory, tools, and techniques * Continuous probability models * The theory of least squares and the analysis of variance * Criteria and methods of estimation * Large sample theory and methods * The theory of statistical inference * Multivariate normal distribution Written for the student and professional with a basic knowledge of statistics, this practical paperback edition gives this industry standard new life as a key resource for practicing statisticians and statisticians-in-training.
1,669 citations
TL;DR: In this article, the authors consider a market with two types of traders, "informed" and "uninformed" traders, and study the operation of the price system as an aggregator of different pieces of information, and show that when there are n-types of traders (n > 1), the price reveals information to each trader which is of higher quality than his own information.
Abstract: I HAVE SHOWN elsewhere that competitive markets can be "over-informationally" efficient. (See Grossman [1975] for this and a review of other work in this area.) If competitive prices reveal too much information, traders may not be able to earn a return on their investment in information. This was demonstrated for a market with two types of traders, "informed" and "uninformed." "Informed" traders learn the true underlying probability distribution which generates a future price, and they take a position in the market based on this information. When all informed traders do this, current prices are affected. "Uninformed" traders invest no resources in collecting information, but they know that current prices reflect the information of informed traders. Uninformed traders form their beliefs about a future price from the information of informed traders which they learn from observing current prices. In the above framework, prices transmit information. However, it is often claimed that prices aggregate information. In this paper we analyze a market where there are n-types of informed traders. Each gets a "piece of information." In a simple model we study the operation of the price system as an aggregator of the different pieces of information. We consider a market where there are two assets; a risk free asset and a risky asset. Each unit of the risky asset yields a return of P1 dollars. P1 will also be referred to as the price of the risky asset in period 1. In period 0 (the current period), each trader gets information about P1 and then decides how much of risky and non-risky assets to hold. This determines a current price of the risky asset, P0, which will depend on the information received by all traders. We assume that the ith trader observes yj, where yi = PI + ,E. There is a noise term, 'E, which prevents any trader from learning the true value of P1. The current equilibrium price is a function of (Y1Y25 ... Yn); write it as PO(Y,Y2, ... 5Yn). The main result of this paper is that when there are n-types of traders (n > 1), PO reveals information to each trader which is of "higher quality" than his own information. That is, the competitive system aggregates all the market's information in such a way that the equilibrium price summarizes all the information in the
1,395 citations
01 Nov 1947
TL;DR: Paul G. Hoel's “Introduction to Mathematical Statistics” seems to me to be an excellent work, and if only it can become generally available it may have a most favourable effect on the situation just described.
1,366 citations