The Business Ethics of Short Selling and Naked Short Selling

The controversy over short selling has continued unabated from the introduction of modern equity trading in Amsterdam in 1610 to the present day. Nevertheless, the business ethics literature has not really addressed short selling. Short sellers not only profit from the misery of others, they also create it through their selling activities. However, they also provide a socially useful service by making prices better reflect true values, protecting other investors from purchasing overpriced securities. Short sellers can also help to provide liquidity in the markets. Recently, there has been a hue and cry against so called “naked” short selling, which involves not delivering the shares that have been sold. This gives manipulators a tool for depressing stock prices and deprives purchasers of voting rights and potential stock lending revenue. Naked short selling creates ethical issues for short sellers, buyers, brokers, market makers, and regulators. Is it ethical to exploit a legal loophole that permits sellers to sell stock and delay delivering shares indefinitely?     

机构投资者的羊群行为能降低投资风险吗?——来自中国上市公司的证据

机构投资者的羊群行为对投资风险影响的实证分析结果表明: 机构投资者存在羊群行为,卖出羊群行为的程度大于买入羊群行为的程度,而且卖出羊群行为加大了投资风险、降低了投资回报率; 买入羊群行为减少了投资风险、提高了投资回报率。因此,加大监管机构投资者卖出羊群行为有利于降低投资风险,并促进证券市场稳定发展。     

LIQUIDATION IN LIMIT ORDER BOOKS WITH CONTROLLED INTENSITY

We consider a framework for solving optimal liquidation problems in limit order books. In particular, order arrivals are modeled as a point process whose intensity depends on the liquidation price. We set up a stochastic control problem in which the goal is to maximize the expected revenue from liquidating the entire position held. We solve this optimal liquidation problem for power‐law and exponential‐decay order book models explicitly and discuss several extensions. We also consider the continuous selling (or fluid) limit when the trading units are ever smaller and the intensity is ever larger. This limit provides an analytical approximation to the value function and the optimal solution. Using techniques from viscosity solutions we show that the discrete state problem and its optimal solution converge to the corresponding quantities in the continuous selling limit uniformly on compacts.     

中国上市公司违规处理信息提前泄露了吗——来自股票流动性和融券交易的证据

本文从股票流动性和融券交易的视角出发,实证检验我国上市公司违规处理信息提前泄露的可能性。研究发现:(1)违规处理公告之前,股票超额非流动性水平和超额融券量显著为正,且与违规处理公告日的超额收益率显著负相关;(2)公告日超额收益率最低组股票的公告前超额非流动性更高,而公告日超额收益率最高组股票的公告前超额融券量更少;(3)当违规处理文件的下批日期与公告日期间隔超过10日时,公告日超额收益率较高的公司股票,其公告前的相对超额融券量显著减少,表明知情交易者占据了主导地位,处理公告的提前泄露更可能解释以上发现。本文的结果表明,监管部门应加强内部管理和提升工作效率,及时公布违规公司处理文件以减少信息提前泄露的可能性,从而有利于股票市场的健康发展。     

Regime‐switching in stock index and Treasury futures returns and measures of stock market stress

We investigate bivariate regime‐switching in daily futures‐contract returns for the US stock index and ten‐year Treasury notes over the crisis‐rich 1997–2005 period. We allow the return means, volatilities, and correlation to all vary across regimes. We document a striking contrast between regimes, with a high‐stress regime that exhibits a much higher stock volatility, a much lower stock–bond correlation, and a higher mean bond return. The high‐stress regime is associated with higher average values of stock‐implied volatility, stock illiquidity, and stock and bond futures trading volume. The lagged implied volatility from equity‐index options is useful in modeling the time‐varying transition probabilities of the regime‐switching process. Our findings support the notions that: (1) stock market stress can have a material influence on Treasury bond pricing, and (2) the diversification benefits of combined stock–bond holdings tend to be greater during times with relatively high stock market stress. © 2009 Wiley Periodicals, Inc. Jrl Fut Mark 30:753–779, 2010     

The Chinese warrant bubble: A fundamental analysis

We investigate the information content in Chinese warrant prices based on an option pricing framework that incorporates short‐selling and margin‐trading constraints in the underlying stock market. We show that Chinese warrant prices can be explained under this pricing framework. On the basis of this new model, we develop a price deviation measure to quantify stock market investors' unobserved demand for short selling or margin trading due to market constraints. We find that warrant‐price deviations are driven by underlying stock valuation to a great extent. Chinese warrant prices, save for the time around expiration dates, are better characterized as derivatives than as pure bubbles.     

Are single stock futures used as an alternative during a short‐selling ban?

The response of the single stock futures (SSF) market to a short‐selling ban is investigated. The hypothesis is that traders use SSF as a substitute instrument for short‐selling. A significant increase in SSF trading activity is documented, accompanied by narrower spreads. SSF market volatility did not react during the ban, which suggests that the increased trading activity did not weaken SSF market quality. The quality of the underlying market during the ban period is also assessed, with the results suggesting that changes in SSF market activity had neither positive nor negative effects on the stocks’ liquidity, volatility, and volume.     

OPTIMAL EXECUTION OF A VWAP ORDER: A STOCHASTIC CONTROL APPROACH

We consider the optimal liquidation of a position of stock (long or short) where trading has a temporary market impact on the price. The aim is to minimize both the mean and variance of the order slippage with respect to a benchmark given by the market volume‐weighted average price (VWAP). In this setting, we introduce a new model for the relative volume curve which allows simultaneously for accurate data fit, economic justification, and mathematical tractability. Tackling the resulting optimization problem using a stochastic control approach, we derive and solve the corresponding Hamilton–Jacobi–Bellman equation to give an explicit characterization of the optimal trading rate and liquidation trajectory.     

Strategic behavior of insiders in initial underpricing and long-run underperformance

We study strategic behavior of insiders in ChiNext IPOs. Since traditional initial underpricing is not appropriate due to the jawbone P/E ratio approach and maximum initial return cap we propose two alternative measures. We identify a significantly positive relationship between insiders' shareholdings and initial underpricing. With no discretion on IPO offer price, the insiders implement earnings management to maintain higher stock prices induced by regulatory changes and high market demand and to facilitate selling their unlocked shares after lockup expiration. We confirm a negative impact from insiders' share sales on long-term performance but don't observe a dramatic underperformance as documented.     

深沪股市1992—2001年季节性波动的实证研究

股票市场季节性波动是股票投资收益的短期波动理论 ,这种现象在许多国家的股票市场中存在。通过对我国股市 1 992至 2 0 0 1年的实证研究 ,发现我国股市出人意料地不存在显著的季节性波动     

RUNNING FOR THE EXIT: DISTRESSED SELLING AND ENDOGENOUS CORRELATION IN FINANCIAL MARKETS

We propose a simple multiperiod model of price impact from trading in a market with multiple assets, which illustrates how feedback effects due to distressed selling and short selling lead to endogenous correlations between asset classes. We show that distressed selling by investors exiting a fund and short selling of the fund’s positions by traders may have nonnegligible impact on the realized correlations between returns of assets held by the fund. These feedback effects may lead to positive realized correlations between fundamentally uncorrelated assets, as well as an increase in correlations across all asset classes and in the fund’s volatility which is exacerbated in scenarios in which the fund undergoes large losses. By studying the diffusion limit of our discrete time model, we obtain analytical expressions for the realized covariance and show that the realized covariance may be decomposed as the sum of a fundamental covariance and a liquidity‐dependent “excess” covariance. Finally, we examine the impact of these feedback effects on the volatility of other funds. Our results provide insight into the nature of spikes in correlation associated with the failure or liquidation of large funds.     

中国股票市场一月效应的实证研究

一月效应是从统计学角度分析股市走势的一种惯常现象,指一月份的回报率往往是"正数",而且会比其他月份为高;相反,十二月的股市回报率很多时候会呈现负值。在传统股市经验里,每逢踏入新一年的一月,股市总是涨的多,跌的少。中国市场是否存在一月效应,投资者能否利用一月效应来获得期望的收益,这些都是研究人员关注的课题。以1997—2007年沪深两市A股指数的日收益率为研究样本,对中国股市是否存在显著的一月效应进行实证研究,结论表明:相对于其他月份而言,中国股市不存在显著的一月效应。     

中国式融资融券与企业金融化——基于分批扩容的准自然实验

本文聚焦于中国经济“脱实向虚”背景下非金融企业金融化问题,将分批次放开融资融券限制作为准自然实验,构造双重差分模型,探究融资融券机制对企业金融化行为的影响。研究发现,融资融券机制的实施总体上会显著地促进企业金融化。这种促进作用主要源于实际交易中占主导地位的融资机制。虽然融券机制对企业金融化有一定的抑制作用,但在融资交易与融券交易高度不对称的情形下,活跃的融资交易加剧了企业配置金融资产的短期投机套利行为。金融资产与经营资产的收益率差距和股价下跌风险是企业调整投资策略的两个关键因素。进一步研究发现,融资融券对企业金融化的影响只存在于管理层持股和机构持股比例较高、产品市场竞争较弱和处于牛市行情等情形中。本文有助于理解中国式融资融券的经济后果,也从制度环境层面为厘清非金融企业“脱实向虚”的内在机制提供了一个新视角。     

The Colombian Stock Market: 1930-1998

Abstract

This article studies the behavior of the stock market in Colombia with the information given by the Bolsa de Bogota Index (Indice de la Bolsa de Bogota, IBB). The index is analyzed from January, 1930 to December, 1998. The inflation rate covers the same period; the inflation rate as measured by the Consumer Price Index. The results of this analysis show that monthly and per annum return-nominal and real-are well below from the expected return of any financial investor. A first hypothesis to explain this is that the investor and entrepreneurs receive benefits that are non-measurable in terms of economic return. Also it can be said that inflation is negative to the return at the stock market, thus: the larger the inflation rate, the smaller the real return. It is shown that the market does not anticipate the future inflation, and of course it is not included in the actual price. Probabilities for selected real return values are presented. The probability to obtain a real return greater than 0% and other values (5%, 10%, 12% and 18%) as well, is much less than 50%. This might show that investing at the stock market is just gambling.     

Mispricing of index futures contracts and short sales constraints

This article examines if changes in short sales constraints affect the extent to which index futures contracts are mispriced. In particular, the study analyzes the mispricing of the Hong Kong Hang Seng Index futures contracts. Tests are conducted over three distinct regulatory regimes relating to the short selling of stocks in Hong Kong. This permits a study of how changes in short selling regulations affect the mispricing of futures contracts. The study indicates that relaxing the constraints on short selling reduces the extent of futures mispricing. Multiple regression analysis is used to test the relationship between the magnitude of mispricing and various economic factors including cash market volatility, time-to-maturity of the contract, trading cost, and dividend payout rates. The study also finds that lifting of the short selling restrictions speeds up market adjustment, especially when a long-hedge (long futures, short stock) signal is detected. © 1999 John Wiley & Sons, Inc. Jrl Fut Mark 19: 695–715, 1999     

GENERAL INTENSITY SHAPES IN OPTIMAL LIQUIDATION

The classical literature on optimal liquidation, rooted in Almgren–Chriss models, tackles the optimal liquidation problem using a trade‐off between market impact and price risk. It answers the general question of optimal scheduling but the very question of the actual way to proceed with liquidation is rarely dealt with. Our model, which incorporates both price risk and nonexecution risk, is an attempt to tackle this question using limit orders. The very general framework we propose to model liquidation with limit orders generalizes existing ones in two ways. We consider a risk‐averse agent, whereas the model of Bayraktar and Ludkovski only tackles the case of a risk‐neutral one. We consider very general functional forms for the execution process intensity, whereas Guéant, Lehalle and Fernandez‐Tapia are restricted to exponential intensity. Eventually, we link the execution cost function of Almgren–Chriss models to the intensity function in our model, providing then a way to see Almgren–Chriss models as a limit of ours.     

Institutional investors,selling pressure and crash risk: Evidence from China

Inconsistent with prior literature on the US stock market, our evidence shows the negative role of institutional investors who exacerbate subsequent crash risk in China. This is because institutional ownership amplifies the selling pressure in response to firm’s bad news, which in turn leads to higher stock price crash risk. The positive relation between institutional ownership and crash risk is more (less) pronounced for transient (dedicated) institutional investors, suggesting the selling pressure of short-term investors is heavier. Additionally, competition of institutional investors strengthens institutional selling pressure and hence exacerbates the effect of institutional ownership on crash risk.     

美国股票回购动机演变对我国回购市场的启示

利用股票回购与每股收益变化之间的关系提供经济信号理论假设,随着美国公司股票回购的日益普遍,已经变得弱化或消失,股票回购的真正价值最终还是回归到股票价格与期望价值之间的经济利益。中国证卷市场上的股票回购开始于1992年,2005年成为市场新热点。在股权分置改革之时,股票回购将会成为中国资本市场新兴的金融工具。但要特别注意对于中小投资者利益的保护,完善股票回购的制度。     

全流通时代大股东股份减持的问题与对策

股权分置改革完成后,大股东所持有的限售股取得了上市流通权。为了满足自身利益最大化的要求,大股东频频在二级市场上进行股份减持。根据我国资本市场的实际,在大股东股权减持的过程中暴露出一些主要问题,所以需要采取一些针对性的对策措施,包括丰富大股东出售股票的渠道,严格信息披露,弱化大股东的信息垄断优势,建立健全大股东股份减持的制度规定等措施。     

股票市场发展与国家资源配置效率:基于股市信息效率视角的研究

中国股票市场发展已经经历20年的历程,很多方面都取得了巨大的发展成就,然而对于股票市场发展对中国经济增长是否产生了显著的正向促进作用,现有研究文献并没有达到一致结论.文章基于股价波动非同步性测度方法,从股票市场信息效率这一新的视角入手,实证检验股票市场发展与国家资源配置效率的因果影响关系,为这一领域研究提供了新的实证证据.实证结果表明:中国股票市场信息效率与国家资源配置效率显著正相关,且这种正相关关系在效益上升行业与下降行业没有显著差别,即高信息效率股票市场能引导社会在高资本回报率的行业内继续追加投资,在低资本回报率的行业内及时削减资本投入,从而提高资源配置效率.因此中国股票市场发展具有较好的经济效应,它对经济增长产生了显著正向促进作用.