The Origin of Stock-Market Crashes: Proposal for A Mimetic Model Using Behavioral Assumptions and an Analysis of Legal Mimicry

Article excerpt


A number of phenomena are responsible for market crashes, but an analysis of investor behavior will tell us more than the valuation of securities on their fundamentals. In this regard, the interpretation of information seems to play a central role in these exceptional events. One specific type of mimetic behavior, called informational mimicry1, sheds light on the kind of sudden, precipitous price plunges seen in 1929, 1987, and 2000.

The current financial crisis certainly exhibits these mechanisms, but one of its novelties is related to a new form of herd behavior arising from the international legislative alignment of financial accounting data. In fact, the new IAS-IFRS standards have produced certain pernicious, globalized effects that may be described as "legal mimicry".

Among the items most commonly blamed for this "Panurgic"2 behavior, Fair Market Valuation and the valuation of financial instruments appear to have been the major mechanisms involved in spreading the crisis. Indeed, they lent support to one of the causes of the current crash, via securitization.

JEL Classification: G01, G11, G14, G18

Keywords: Stock-market crises; Behavioral finance; Informational and legal mimicry; IAS-IFRS standard


A crash is a precipitous collapse of listed assets. It must be violent and spectacular, and must cause serious collateral damage.

Its suddenness arises from a recurrent process: an upturn in the economy attracts investors of every sort, and this inrush of capital feeds the further expansion of the market. The process then becomes uncontrollable if investors borrow money to invest in the market. The value of the securities thus becomes detached from the value of the listed companies, as determined according to the basic criteria employed by market analysts.

This discrepancy in valuation feeds an over-valuation of the market, called a speculative bubble. In this case investors decide both to quit the market and abandon any possible remaining speculative profits, or to stay in while nevertheless awaiting any data, news, information, or even rumors that might deliver "the signal" that will burst the bubble and bring down the markets.

A number of phenomena are responsible for crashes, but the mimetic aspects of investor behavior and standards outweigh the valuation of securities on their fundamentals. The dynamics of crashes thus appear to be behavioral in nature.3 Daniel Khaneman received the 2002 Nobel Prize in Economics for his work on decision-making under uncertainty. His work gave birth to behavioral finance4, one of the two themes of this article, which seeks to explain the current financial crisis5. Traditional finance has evidently become incapable of explaining our successive crashes. On the one hand, the various explanations put forward for these phenomena are inadequate (for example, explanations for the 1987 crash are unsatisfactory in that they ignore the interpretational aspect of data, news, information, and rumors, which is a central feature of this type of event). On the other hand, the assumption that they are caused by rational actions is very much open to question, being unable to explain why bubbles appear, and still less what causes them to burst.

The first part of the article proposes a model that incorporates behaviors that are more "realistic" and familiar to market actors, so as to provide answers concerning the mechanisms that bring about crashes. This model is derived from the theory of informational cascades (Bikhchandani, Hirshleifer, and Welch, 1992), which we have adapted for application to financial markets. The constraint of rationality will thus be removed and behaviors involving over- and under-confidence will be introduced. Overconfidence is one of the behavioral biases most frequently discussed in the academic literature, and for some authors (De Bondt and Thaler, 1995) the fact that individuals may be overconfident is perhaps the most robust finding in the field of the psychology of judgment. …


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