We provide a model in which a single psychological constraint, limited attention, explains both under- and overreaction to different earnings components. Investor neglect of earn-ings induces post-earnings announcement drift and the profit anomaly. Neglect of earnings components causes accrual and cash flow anomalies. The model offers empirical implica-tions relating the strength of earnings-related anomalies to the forecasting power of current earnings-related information for future earnings, investor attentiveness, and the volatilities of and correlation between accruals and cash flows. We also show that, owing to atten-tion costs, in equilibrium not all investors choose to attend to earnings or its components. (JEL G12, G14, M41, M43) Market reactions to earnings and earnings components present a striking puzzle. Stock prices on average underreact to earnings surprises (post-earnings an-nouncement drift), but overreact to the operating accruals component of earn-ings.1 Earnings- and accruals-related patterns of return predictability are often referred to as “anomalies, ” “under- ” and “overreaction, ” or reflecting investor “optimism, ” “pessimism, ” or “naı̈veté. ” Such labels offer little guidance as to

[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.]

[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.]

Evidence indicates that people fear change and the unknown. We model this behavior as familiarity bias in which individuals focus on adverse scenarios in evaluating defections from the status quo. The model explains portfolio underdiversification, home and local biases. More importantly, equilibrium stock prices reflect an unfamiliarity premium. In an international setting, our model predicts that while the standard CAPM fails to hold with respect to the world market portfolio, a modified CAPM holds wherein the market portfolio is replaced with a portfolio of the stock holdings of investors not subject to familiarity bias.

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. The Author 2011. 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.