The basic paradigm of asset pricing is in vibrant flux. The purely rational approach is being subsumed by a broader approach based upon the psychology of investors. In this approach, security expected returns are determined by both risk and misvaluation. This survey sketches a framework for understanding decision biases, evaluates the a priori arguments and the capital market evidence bearing on the importance of investor psychology for security prices, and reviews recent models.

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.

In existing models of information acquisition, all informed investors receive their information at the same time. This article analyzes trading behavior and equilibrium information acquisition when some investors receive common private information before others. The model implies that, under some conditions, investors will focus only on a subset of securities ('herding'), while neglecting other securities with identical exogenous characteristics. In addition, the model is consistent with empirical correlations that are suggestive of oft-cited trading strategies such as profit taking (short-term position reversal) and following the leader (mimicking earlier trades).

An informational cascade occurs when it is optimal for an individual, having observed the actions of those ahead of him, to follow the behavior of the preceding individual without regard to his own information. We argue that localized conformity of behavior and the fragility of mass behaviors can be explained by informational cascades.

This paper examines equilibrium in a spot and futures market with both primary producers (growers) and intermediate producers (processors). For a commodity that is subject to output shocks, processors tend to hedge long, in contrast with Hick's theory of futures hedging. Nevertheless, if transaction costs are low, the two-stage production process brings about a downward futures price bias, consistent with Hick's pricing prediction. But if costs of trading futures are high, growers tend to be differentially driven from the futures market, reversing the direction of the bias. Futures trading may also affect the organization of industry; when demand is inelastic, futures trading can serve as a substitute for vertical integration as a means of diversifying risk because the risk positions of growers are complementary with those of processors.

[We find a positive association between short selling and accruals during 1988—2009, and that asymmetry between the up- and downsides of the accrual anomaly is stronger when constraints on short arbitrage are more severe (low availability of loanable shares as proxied by institutional holdings). Short arbitrage occurs primarily among firms in the top accrual decile. Asymmetry is present only on NASDAQ. Thus, there is short arbitrage of the accrual anomaly, but short-sale constraints limit its effectiveness.]

This article studies information blockages and the asymmetric release of information in a security market with fixed setup costs of trading. In this setting, "sidelined" investors may delay trading until price movements validate their private signals. Trading thereby internally generates the arrival of further news to the market. This leads to (1) negative skewness following price run-ups and positive skewness following price rundowns (even though the model is ex ante symmetric), (2) a lack of correspondence between large price changes and the arrival of external information, and (3) increases in volatility following large price changes.

We examine how investor preferences and beliefs affect trading in relation to past gains and losses. The probability of selling as a function of profit is V-shaped; at short holding periods, investors are more likely to sell big losers than small ones. There is little evidence of an upward jump in selling at zero profits. These findings provide no clear indication that realization preference explains trading. Furthermore, the disposition effect is not driven by a simple direct preference for selling a stock by virtue of having a gain versus a loss. Trading based on belief revisions can potentially explain these findings. The Author 2012. Published by Oxford University Press on behalf of The Society for Financial Studies. All rights reserved. For Permissions, please e-mail: [email protected]., Oxford University Press.

[We examine how experience affects the decisions of individual investors and institutions in IPO auctions to bid in subsequent auctions, and their bidding returns. We track bidding histories for all 31,476 individual investors and 1,232 institutional investors across all 84 IPO auctions during the period from 1995 to 2000 in Taiwan. For individual bidders, (1) high returns in previous IPO auctions increase the likelihood of participating in future auctions; (2) bidders' returns decrease as they participate in more auctions; (3) auction selection ability deteriorates with experience; and (4) those with greater experience bid more aggressively. These findings are consistent with naïve reinforcement learning wherein individuals become unduly optimistic after receiving good returns. In sharp contrast, there is little sign that institutional investors exhibit such behavior.]