ADAPTIVE EXPECTATIONS AND STOCK MARKET CRASHES*

A theory is developed that explains how stocks can crash without fundamental news and why crashes are more common than frenzies. A crash occurs via the interaction of rational and naive investors. Naive traders believe that prices follow a random walk with serially correlated volatility. Their expectations of future volatility are formed adaptively. When the market crashes, naive traders sell stock in response to the apparent increase in volatility. Since rational traders are risk averse as well, a lower price is needed to clear the market: The crash is a self‐fulfilling prophecy. Frenzies cannot occur in this model.     

Market Dynamics,Programmed Traders and Futures Markets: Beginning the Laboratory Search for a Smoking Gun

Recent events have caused a re-examination of the role of programmed traders and futures markets in generating destabilizing price movements. Laboratory experiments provide an ideal environment to isolate their effects on behaviour. In a new series of experiments we find that program traders and futures markets can be crucial for ensuring the informational efficiency of the spot market, even when the former are active participants in bubbles and crashes     

When and Where Are Informed Traders? What Is Their Relationship with Analysts in the Price Discovery Process?

The authors' aim was to analyze the influence of analysts' recommendations on the activity of informed and uninformed traders and whether such influence produces changes in the price discovery process. The analysis was carried out in the Spanish market, considered to be an ideal market given its characteristics. The authors' results indicate that although investors as a whole react to new information from analysts and their activity increases, this reaction is not independent of the type of stock. Informed traders do not increase their activity with small stocks to the same extent as uninformed investors do. Furthermore, the influence of these movements on price discovery is not significant. The results suggest that the interpretation role of analysts is more important for less accessible firms in terms of assessing their growth opportunities. This role may enhance the herding behavior of uninformed agents trading in those small titles for which they would otherwise need to invest extra time and extra money for taking profitable decisions.     

Rock around the clock: An agent-based model of low- and high-frequency trading

We build an agent-based model to study how the interplay between low- and high-frequency trading affects asset price dynamics. Our main goal is to investigate whether high-frequency trading exacerbates market volatility and generates flash crashes. In the model, low-frequency agents adopt trading rules based on chronological time and can switch between fundamentalist and chartist strategies. By contrast, high-frequency traders activation is event-driven and depends on price fluctuations. High-frequency traders use directional strategies to exploit market information produced by low-frequency traders. Monte-Carlo simulations reveal that the model replicates the main stylized facts of financial markets. Furthermore, we find that the presence of high-frequency traders increases market volatility and plays a fundamental role in the generation of flash crashes. The emergence of flash crashes is explained by two salient characteristics of high-frequency traders, i.e., their ability to i. generate high bid-ask spreads and ii. synchronize on the sell side of the limit order book. Finally, we find that higher rates of order cancellation by high-frequency traders increase the incidence of flash crashes but reduce their duration.     

Limit order books,uninformed traders and commodity derivatives: Insights from the European carbon futures

This paper provides a suitable model for studying the strategic behavior of uninformed investors that trade commodity derivatives via limit order books. Two main testable implications are obtained after solving for the model equilibrium. The adverse selection costs of uninformed traders depend on the inflow of market orders and their risk aversion. Next, the adverse selection costs of uninformed buyers and sellers and the difference of their asset valuations determine the size of their bid-ask spread.An analysis of European carbon futures data confirms the relevance of these implications. Moreover, we detect a diagonal effect that results in a positive correlation of market orders, which is driven by adverse selection, then by order splitting strategies and by imitative strategies of uninformed traders to a lesser extent.     

The Effects of Subject Pool and Design Experience on Rationality in Experimental Asset Markets

Empirical evidence suggests that prices do not always reflect fundamental values and individual behavior is often inconsistent with rational expectations theory. We report the results of fourteen experimental asset markets designed to examine whether the interactive effect of subject pool and design experience (i.e., previous experience in a market under identical conditions) tempers price bubbles and improves forecasting ability. Our main findings are: 1) price run-ups are modest and dissipate quickly when traders are knowledgeable about financial markets and have participated in a previous market under identical conditions; 2) price bubbles moderate quickly when only a subset of traders are knowledgeable and experienced; 3) the heterogeneity of expectations about price changes is smaller in markets with knowledgeable and experienced traders, even if such traders only represent a subset of the market; and 4) individual forecasts of prices are not consistent with the predictions of the rational expectations model in any market, although absolute forecast errors are smaller for subjects who are knowledgeable of financial markets and for those subjects who have participated in a previous market. In sum, our findings suggest that markets populated by at least a subset of knowledgeable and experienced traders behave rationally, even though average individual behavior can be characterized as irrational.     

Strategic noise traders and liquidity pressure with a physically deliverable futures contract

Do physically deliverable futures contracts induce liquidity pressure in the underlying spot market? The answer is believed to be no since the asset is delivered sometimes after the expiration of the contract so that the futures trader's payoff does not clearly depend on the price of the underlying stock at expiration. We construct a rational expectations equilibrium model in which a strategic uninformed trader induces liquidity pressure in the underlying spot market at the expiration of a physically deliverable futures contract. Liquidity pressure is the result of a pure informational advantage: if it is known that futures traders hedge their position in the spot market then a strategic trader with no information about the fundamental value of the underlying has an incentive to create noise in the futures market in order to gain information on the composition of the spot order flow at future auctions. We show that informed traders benefit from this form of strategic noise and that the efficiency of the prices remains unaffected.     

SHAKEOUTS AND MARKET CRASHES*

This article provides a microfoundation for the rise in optimism that seems to precede market crashes. Small, young markets are more likely to experience stock‐price run‐ups and crashes. We use a Zeira–Rob type of model in which demand size is uncertain. Optimism then grows rationally if traders' prior distribution over market size has a decreasing hazard. Such prior beliefs are appropriate if most new markets are duds and only a few reach a large size. The crash occurs when capacity outstrips demand. As an illustration, for the period 1971–2001 we fit the model to the Telecom sector.     

Limit orders,asymmetric information,and the formation of asset prices with a computerized specialist

We analyze the existence of equilibrium in an asset market under asymmetric information. Price formation is modeled as a bilateral sealed bid auction where uninformed and informed traders submit limit orders to a computerized specialist. The computerized specialist is programmed to sell to the highest bidder and buy from the seller asking the lowest price. We show that this mechanism — which is designed to model the Globex and RAES trading institutions used in Chicago, London, New York, Paris, and Germany — yields an equilibrium in which the bid-ask spread is endogenously random and the passive specialist earns nonnegative profits.     

Don’t let your robots grow up to be traders: Artificial intelligence, human intelligence, and asset-market bubbles

Researchers who have examined markets populated by “robot traders” have claimed that the high level of allocative efficiency observed in experimental markets is driven largely by the “intelligence” implicit in the rules of the market. Furthermore, they view the ability of agents (artificial or human) to process information and make rational decisions as unnecessary for the efficient operation of markets. This paper presents a new series of market experiments that show that markets populated with standard robot traders are no longer efficient if time is a meaningful element, as it is in all asset markets. While simple two-season markets with human subjects reliably converge to an efficient equilibrium, markets with minimally intelligent robot traders fail to attain this equilibrium. Instead, these markets overshoot the equilibrium and then crash below it. In addition to firmly establishing the role of trader intelligence in asset-market equilibrium, these experiments also provide insights into why bubbles and crashes are consistently observed in many asset-market laboratory experiments using human subjects.     

Asymmetric effect of margin-trading activities on price crashes: evidence from Chinese stock market

Prior literature on the impact of margin-trading activity on stock price crashes is mixed and does not reach consensus. Using data from a Chinese margin-trading pilot programme initiated in 2010, this article employs both margin-buying and margin-covering activities to investigate the asymmetric impact on stock price crashes. We find that margin-buying activities are beneficial reducing the price crash prone, especially in bad times. In contrast, margin-covering activities amplify price crashes in both good times and bad times.     

Market Crashes and Informational Avalanches

This paper analyses a security market with transaction costs and a sequential trading structure. Transaction costs may prevent many traders from revealing their private information if they trade in a sequential fashion. Due to the information aggregation failure, hidden information gets accumulated in the market which may be revealed by a small trigger, yielding a high volatility in the absence of an accompanying event. The paper first characterizes the optimal trading strategy of the agent which constitute the unique equilibrium. Further properties of the price sequence are obtained using the concepts of informational cascade and informational avalanche.
The results are applied to the explanation of market crashes. In particular, the dynamics of market crashes are illustrated as evolving through the following four phases: (1) boom; (2) euphoria; (3) trigger; and (4) panic; where the euphoria corresponds to the informational cascade and the panic corresponds to the informational avalanche.     

Short sale constraints and the information content of trading

We examine changes in the information content of trading when short sale constraints between prohibition and restriction exist on a stock exchange. This is made possible by a unique institutional arrangement at the Stock Exchange of Hong Kong. It maintains a list of stocks which can be sold short under regulations. Stocks not on the list are prohibited from short selling. The list is revised on a quarterly basis based on predetermined criteria. We find that the probability of information-based trading (PIN) significantly increases when a stock is added to the list. Further analysis shows that this is mainly because uninformed traders are driven out of the market. Elimination of uninformed traders also causes the aggregate trading volume to decrease rather than increase. In comparison, the PIN does not change when a stock is dropped from the list. We also find that market liquidity, measured by volatility and bid–ask spreads, slightly decreases when a stock is added to the list and significantly increases when a stock is dropped from the list. Possible explanations are discussed.     

保险资金持股与股价崩盘风险——市场“稳定器”还是崩盘“加速器”?

现阶段,有关保险资金持股与资本市场稳定相互关系的讨论多止于推测,少有学者以大样本数据进行实证考察。在理论上,保险资金持股上市公司,一方面可以抑制经理人负面信息隐藏,作为市场“稳定器”降低股价暴跌风险;另一方面,也能引发投资者跟风炒作,导致市场情绪高涨和股价高估,成为股价崩盘风险的“加速器”。本文基于2007—2016年中国沪深两市A股上市公司的数据,实证分析保险资金持股上市公司是否加剧市场暴跌及其作用机制。结果显示:保险资金持股加剧了股价崩盘风险,是公司股价崩盘的“加速器”。这一结论在经过DID模型、工具变量回归、PSM+OLS等内生性分析,以及稳健性检验之后依然成立。进一步研究表明,相比于民营、小型和财产保险公司,在股市投资规模更大的国有、大型和人寿保险公司更能引发市场跟风炒作,加剧股价崩盘风险;不过,当保险资金作为前十大股东参与公司治理时则能够降低股价崩盘风险。本文不仅为保险资金持股与资本市场稳定相互关系的讨论提供了经验证据,也为规范保险资金股权投资,维护资本市场稳定提供有益借鉴。     

The “inflow-effect”—Trader inflow and price efficiency

We investigate the impact of cash and trader inflow on price efficiency in multi-period experimental asset markets. Implementing eight treatments with 672 subjects, we find that (i) the joint inflow of cash and traders triggers strong overvaluation and massive price run-ups (inflow-effect). Remarkably, the effect occurs in almost all of the 30 markets with joint cash and trader inflow and is very robust. The effect even prevails in markets with complete and symmetric fundamental information. We further show that (ii) in treatments with the joint inflow of cash and traders, prices crash to fundamentals towards maturity of the asset. The analysis of traders׳ beliefs reveals that (iii) despite fundamental values staying constant, beliefs about fundamentals co-move with upwardly trending prices. Finally, we report a speculative motive only among the optimists in treatments where we observe the inflow-effect.     

The existence of fully rational expectations approximate equilibria with noisy price observations

Nonrevealing fully rational expectations approximate equilibria exist in microeconomic pure exchange economies in which uninformed agents have suitably dispersed noisy price observations. Such traders maximize a state-dependent expected utility conditional on the price vector they observe, the distributions of noisy price observations, and the correct equilibrium relationship between states of the world and prices. In equilibrium, aggregate excess demand is small with high probability in every state of the world (and its expectation is also small); this magnitude diminishes as the noisy price observations become more accurate. Equilibria are obtained by applying a fixed point argument to state-dependent excess demand functions which are smooth because of the noisy price observations.     

异质信念、投机均衡与农产品期货定价*

农产品期货市场套利并不充分,交易者也不是完全理性的。本文假设农产品期货市场有限套利、交易者异质信念并遵循“经验法则”预期,构建了农产品期货投机均衡定价模型,并认为集中竞价规则下产生的农产品期货价格是由交易者的预期决定的;前期期货价格水平、现货价格和前期期货价格的变动趋势、不同类型交易者的比例结构及其预期模式共同影响农产品期货价格的形成与波动;基本分析法交易者占主导地位的农产品期货市场具有更高的套期保值与价格发现效率。针对中国七种主要农产品期货的实证结果显示,农产品期货投机均衡定价模型对解释中国农产品期货价格的形成与波动是有效的。这意味着在期货行情系统中实时披露现货价格信息,培育和引导交易者运用基本分析法预测期货价格走势,有助于提升农产品期货市场的效率。     

Conservative traders,natural selection and market efficiency

This paper examines the impact of conservative traders on market efficiency in an evolutionary model of a commodity futures market. This paper shows that the long-run market outcome is informationally efficient, as long as in every period there is a positive probability that entering traders are more conservative than their predecessors. Conservative traders are those who correctly predict the spot price with a positive probability, and more importantly, who in their mistakes err on the side of caution, and rarely overpredict the spot price as buyers, and underpredict the spot price as sellers. This result does not require entry of traders with better information than their predecessors.     

Market manipulation with sentiment traders

This article offers a new perspective for traders’ sentiment by bridging the relationship between feedback effect and market manipulation. Allowing access to information regarding manipulated orders confuses sentiment traders, leading to an overestimation of the true asset value which actually remains the same. We find that sentiment factor has a nonmonotonic impact on the responsiveness to order information and price informativeness. Furthermore, it is shown that informed traders behave like a contrarian, and can use order information to reassess the price, which results in the multiplicity of equilibria.     

A note on welfare-improving ignorance about quality

Consider a monopolist that is selling a high quality product when the quality is unknown to a fraction of the consumers. If the quality cannot be signaled and the fraction is sufficiently large, then the monopolist will offer a low price to induce uninformed consumers to buy. If the fraction is sufficiently small, then uninformed consumers are irrelevant to its optimal price. If the uninformed consumers are priced out of the market as a result, then welfare can decrease. I am very grateful for the comments of two anonymous referees that have significantly improved this paper.