信息不对称、过度自信与股价变动

信息传导的非同步和投资者情绪变化是股票市场的两个典型特征,前者会引发投资者之间出现信息不对称问题,后者主要体现为投资者过度自信,两者共同作用影响股票价格变动。本文将信息不对称和投资者过度自信情绪置于同一个分析框架,建立两阶段动态序贯定价理论模型研究现实市场上信息传导过程中股价变动的内在机制。结果表明:(1)面临新信息的进入,投资者对股票收益预期的调整与均衡价格之间具有正相关关系;(2)面临有利消息时,过度自信投资者比例越大,股票的均衡价格越高,投资收益将越低;面临不利消息时则相反;(3)随着过度自信投资者比例以及过度自信程度升高,市场风险溢价将下降;(4)投资者群体在信息传导过程中出现分化,对股价变动形成异质信念,未获取信息和获取信息但未出现过度自信的投资者认为股价被高估,获取信息且出现过度自信的投资者认为价格被低估,促使更多的交易,引发市场成交量和股价变动;(5)过度自信投资者比例与过度自信程度提高均会对市场效率产生正向影响,而对市场深度具有负向效应。最后,基于理论结果对非对称性和持续性等典型的市场波动性特征进行解释。     

Which past returns affect trading volume?

Anecdotal evidence suggests and recent theoretical models argue that past stock returns affect subsequent stock trading volume. We study 3,000 individual investors over a 51 month period to test this apparent link between past returns and volume using several different panel regression models (linear panel regressions, negative binomial panel regressions, Tobit panel regressions). We find that both past market returns as well as past portfolio returns affect trading activity of individual investors (as measured by stock portfolio turnover, the number of stock transactions, and the propensity to trade stocks in a given month). After high portfolio returns, investors buy high risk stocks and reduce the number of stocks in their portfolio. High past market returns do not lead to higher risk taking or underdiversification. We argue that the only explanations for our findings are overconfidence theories based on biased self-attribution and differences of opinion explanations for high levels of trading activity.     

Overconfidence among option traders

The investor overconfidence theory predicts a direct relationship between market‐wide turnover and lagged market return. However, previous research has examined this prediction in the equity market, we focus on trading in the options market. Controlling for stock market cross‐sectional volatility, stock idiosyncratic risk, and option market volatility, we find that option trading turnover is positively related to past stock market return. In addition, call option turnover and call to put ratio are also positively associated with the past stock market return. These findings are consistent with the overconfidence theory. We also find that overconfident investors trade more in the options market than in the equity market. We rule out explanations other than investor overconfidence, such as momentum trading and varying risk preferences, for our findings.     

The overconfidence of investors in the primary market

We analyze the investment performance of 6993 investors bidding in 77 discriminatory IPO auctions in the Taiwan stock market between January 1996 and April 2000, and find that frequent bidders in these auctions have lower returns than infrequent bidders. The frequent bidders bid too aggressively and evaluate the IPO firms too optimistically, resulting in inferior performance. Despite being quite successful in their first few auction bids, the returns for frequent investors are gradually reduced in subsequent auctions. The multivariate model and the analysis of the possibility of perverse incentives of brokerage firms suggest that our findings cannot be explained by rational hypotheses, whereas in contrast, the theories on overconfidence and self-attribution bias can explain the increase in bidding frequency and the deterioration in return performance for bidders in IPO auctions.     

Partial Adjustment or Stale Prices? Implications from Stock Index and Futures Return Autocorrelations

We investigate the relation between returns on stock indicesand their corresponding futures contracts to evaluate potentialexplanations for the pervasive yet anomalous evidence of positive,short-horizon portfolio autocorrelations. Using a simple theoreticalframework, we generate empirical implications for both microstructureand partial adjustment models. The major findings are (i) returnautocorrelations of indices are generally positive even thoughfutures contracts have autocorrelations close to zero, and (ii)these autocorrelation differences are maintained under conditionsfavorable for spot-futures arbitrage and are most prevalentduring low-volume periods. These results point toward microstructure-basedexplanations and away from explanations based on behavioralmodels.     

Managerial Overconfidence,Self-Attribution Bias,and Downwardly Sticky Investment: Evidence from Korea

The extant literature on behavioral corporate finance has explored the effects of overconfidence on investment–cash flow sensitivity (ICS) to explain overinvestment, yet it has overlooked the asymmetric behavior of investments in relation to changes in cash flow levels. This study examines whether investments behave asymmetrically responding to changes in cash flows and, if so, how managerial overconfidence affects asymmetric ICS. Using a sample of KOSPI and KOSDAQ firms in Korea, we find the incidence of downwardly sticky ICS in unconstrained firms. We then find that overconfident managers encourage ICS to be stickier than their rational peers do in unconstrained firms. Finally, we find that managerial overconfidence intensified by self-attribution bias induces ICS to get even stickier, suggesting more explicit evidence of corporate investment distortions. The results of alternative tests using the asymmetric models of Homburg and Nasev (2008) are qualitatively consistent with prior results. Overall, our findings imply a higher incidence of excessive investment commitments driven by overconfident managers.     

The impact of portfolio diversification on mean reverting components of stock indices

Positive autocorrelations are introduced into stock index portfolios when they are formed from individual stock indices while negative autocorrelations are induced in returns by increasing the investment horizon. Using monthly data of six international stock indices, this paper examines the diversification effect with different investment horizons on autocorrelations of stock index portfolios. The results show that portfolio diversification does not alter the impact of the investment horizon on autocorrelations. Different investment horizons, however, have great impact on the diversification effect on autocorrelations. With short (long) horizons, the average autocorrelation coefficient increases (decreases) with an increase in the portfolio size, suggesting that mean-reverting component dominates the delayed adjustment effect in long horizons and vice versa in short horizons. Our results are robust across two 10-year sub-periods.The author would like to thank an anonymous referee of this Journal for the comments on an earlier version of this paper and the Research Committee of Hong Kong Baptist University for the financial support in this research.     

An empirical evaluation of the overconfidence hypothesis

Recently, several behavioral finance models based on the overconfidence hypothesis have been proposed to explain anomalous findings, including a short-term continuation (momentum) and a long-term reversal in stock returns. We characterize the overconfidence hypothesis by the following four testable implications: First, if investors are overconfident, they overreact to private information and underreact to public information. Second, market gains make overconfident investors trade more aggressively in subsequent periods. Third, excessive trading of overconfident investors in securities markets contributes to the observed excessive volatility. Fourth, overconfident investors underestimate risk and trade more in riskier securities. To document the presence of overconfidence in financial markets, we empirically evaluate these four hypotheses using aggregate data. Overall, we find empirical evidence in support of the four hypotheses.     

Chief financial officer overconfidence and stock price crash risk

Numerous studies have shown the prevalence of overconfidence among Chief Financial Officers (CFOs). Surprisingly, the real effect of CFO overconfidence is under-researched. Using data from a large sample of US-listed firms over the period 1993–2019 and adopting an eclectic theoretical approach, we find that overconfident CFOs are more likely to increase stock price crash risk than non-overconfident CFOs through risk-taking and bad news hoarding. These findings pass a series of robustness tests. Furthermore, departing from most overconfident studies that merely examine one type of top managers (i.e., Chief Executive Officer (CEO)), we consider the influence of CEO and CFO overconfidence jointly. Interestingly, we find that CFO overconfidence outweighs CEO overconfidence in influencing stock price crash risk. Moreover, the overconfidence effect is intensified when overconfident CFOs collaborate with overconfident CEOs, thus raising stock price crash risk. However, stronger governance and a transparent information environment constrain overconfident CFOs' effect on stock price crash risk. Overall, our findings highlight the importance of CFO overconfidence in determining stock return tail risks.     

Individualism and Momentum around the World

This paper examines how cultural differences influence the returns of momentum strategies. Cross-country cultural differences are measured with an individualism index developed by Hofstede (2001) , which is related to overconfidence and self-attribution bias. We find that individualism is positively associated with trading volume and volatility, as well as to the magnitude of momentum profits. Momentum profits are also positively related to analyst forecast dispersion, transaction costs, and the familiarity of the market to foreigners, and negatively related to firm size and volatility. However, the addition of these and other variables does not dampen the relation between individualism and momentum profits.     

Investigation of investors' overconfidence, familiarity and socialization

This study, using a sample of New Zealand investors, investigates three behavioural finance theories: investor overconfidence, socialization and the familiarity effect. We find support for the investor overconfidence theory, using characteristics such as past success, optimism, confidence in one's abilities, investment experience and investment‐related knowledge. Concerning the socialization theory, we observe that the investors actively sought information regarding the stock market, 75 per cent doing this on a weekly basis. Those investors that kept themselves informed daily outperformed other investors by 8 per cent. The familiarity effect was confirmed, showing investors to hold a far too high proportion of local stocks, although the majority of investors believed international equity markets would provide returns that were either better or equal to New Zealand stocks.     

Opportunism,overconfidence and irrationality: A puzzling triad

We empirically investigate managerial decision-making in a corporate context with combinations of rational/irrational managers and investors. There are noticeable differences in insider trading among these groups, particularly when exposed to market-wide and firm-level sentiment. We find that investor sentiment in the presence of managerial overconfidence has a significant impact on insider trading. We also show that managers behave opportunistically when timing stock splits and undertaking insider trading. Our findings linking splits to insider trading is robust under various specifications. In cases where irrational managers coexist with irrational investors, our study demonstrates important implications for the firms involved.     

A Time-Series Model of Stock Returns with a Positive Short-Term Correlation and a Negative Long-Term Correlation

We study portfolio stock return behavior that exhibits both a positive autocorrelation over short horizons and a negative autocorrelation over long horizons. These autocorrelations are more significant in small size portfolios. Among various forms of temporary components in stock prices, an AR(2) component is the simplest model compatible with this pattern of returns, which yields an ARMA(2,2) model of stock returns. We show that the significance of this model is that it requires the presence of feedback trading, which is a form of irrational trades, and the market's slow adjustment to the market fundamentals, which is consistent with recent modelings of stock prices. We find that the variation of the temporary component becomes greater as the firm size gets smaller. This implies that the deviation from the market fundamentals is larger in small size portfolios than in large size portfolios.     

S&P 500 trading strategies and stock betas

This paper shows that S&P 500 stock betas are overstatedand the non-S&P 500 stock betas are understated becauseof liquidity price effects caused by the S&P 500 tradingstrategies. The daily and weekly betas of stocks added to theS&P 500 index during 1985-1989 increase, on average, by0.211 and 0.130. The difference between monthly betas of otherwisesimilar S&P 500 and non-S&P 500 stocks also equals 0.125during this period. Some of these increases can be explainedby the reduced nonsynchroneity of S&P 500 stock prices,but the remaining increases are explained by the price pressureor excess volatility caused by the S&P 500 trading strategies.I estimate that the price pressures account for 8.5 percentof the total variance of daily returns of a value-weighted portfolioof NYSE/AMEX stocks. The negative own autocorrelations in S&P500 index returns and the negative cross autocorrelations betweenS&P 500 stock returns provide further evidence consistentwith the price pressure hypothesis.     

Overconfidence,risk perception and the risk-taking behavior of finance professionals

This paper highlights the role played by overconfidence and risk perception in the risk-taking behaviors of finance professionals. We interviewed 64 high-level professionals and demonstrate that they are overconfident in both the general and the financial domains. Using a recent measure proposed by Glaser et al. (2013), we indicate that respondents are overconfident in forecasting future stock prices. We demonstrate that the risk they are willing to assume is positively influenced by overconfidence and optimism and negatively influenced by risk perception. However, the stock return volatility anticipated is, in most cases, an insignificant determinant of the risk that professionals are ready to assume.     

Investor Overconfidence and Trading Volume

The proposition that investors are overconfident about theirvaluation and trading skills can explain high observed tradingvolume. With biased self-attribution, the level of investoroverconfidence and thus trading volume varies with past returns.We test the trading volume predictions of formal overconfidencemodels and find that share turnover is positively related tolagged returns for many months. The relationship holds for bothmarket-wide and individual security turnover, which we interpretas evidence of investor overconfidence and the disposition effect,respectively. Security volume is more responsive to market returnshocks than to security return shocks, and both relationshipsare more pronounced in small-cap stocks and in earlier periodswhere individual investors hold a greater proportion of shares.(JEL G11, G12)     

The determinants of quantile autocorrelations: Evidence from the UK

We empirically analyse the cross-sectional determinants of stock return autocorrelations in the UK in different quantiles of conditional return distributions. Autocorrelations in low quantiles are predominantly positive, whereas those in the remaining quantiles are negative. Autocorrelations in different quantiles depend on different sets of firm and trading characteristics: when returns are normal or high, prices react quickly to information, are driven by positive feedback traders, instantaneous news arrivals, and overshoot, trades are predominantly motivated by hedging/liquidity needs, and measured autocorrelations can be biassed by the bid–ask bounce effect and nonsynchronous trading. However, when returns are unusually low, prices are driven by information arriving sequentially and react sluggishly to it, and are influenced by trading on private information and/or negative feedback traders.     

Excess corporate payouts and financial distress risk

Firms that follow excessive payout policies (over-payers) are higher on the financial distress spectrum and have lower survival rates than under-payers. In addition, over-payers endure lower future sales and asset growth than under-payers and experience negative abnormal returns in the bond and stock markets. Exogenous import tariff reductions and commodity price jumps reduce the likelihood of overpayment. We interpret this as evidence consistent with financial flexibility considerations, rather than risk-shifting, explaining the decision to overpay. We also find that CEO overconfidence and catering incentives affect overpayment.     

Financial overconfidence over time: Foresight,hindsight, and insight of investors

Financial overconfidence leads to increased trading activity, higher risk taking, and less diversification. In a panel survey of online brokerage clients in the UK, we ask for stock market and portfolio expectations and derive several overconfidence measures from the responses. Overconfidence is identified in the sample in various forms. By matching survey data with participants’ transactions and portfolio holdings, we find an influence of overplacement on trading activity, of overprecision and overestimation on diversification, and of overprecision and overplacement on risk taking. We explore the evolution of overconfidence over time and identify a role of past success and hindsight on subsequent investor overconfidence in line with learning to be overconfident.     

Arrogance can be a virtue: Overconfidence,information acquisition,and market efficiency

In behavioral finance, overconfidence has been established as a prevalent psychological bias, which can make markets less efficient by creating mispricing in the form of excess volatility and return predictability. In this paper, we develop a model in which overconfidence causes investors to overinvest in information acquisition when this information could improve market efficiency by driving prices closer to true values. We study the impact of overconfidence on mispricing and information acquisition, comparing their net effect on prices. We derive several novel implications. First, overconfidence generally improves market pricing provided the level of overconfidence is not too high. Pricing can also improve even when overconfidence is arbitrarily high, depending on the amount of private information acquired relative to publicly available information.