We explore behavioral explanations for sub-optimal corporate investment decisions. Focusing on the sensitivity of investment to cash flow, we argue that personal characteristics of chief executive officers, in particular overconfidence, can account for this widespread and persistent investment distortion. Overconfident CEOs overestimate the quality of their investment projects and view external finance as unduly costly. As a result, they invest more when they have internal funds at their disposal. We test the overconfidence hypothesis, using data on personal portfolio and corporate investment decisions of CEOs in Forbes 500 companies. We classify CEOs as overconfident if they repeatedly fail to exercise options that are highly in the money, or if they habitually acquire stock of their own company. The main result is that investment is significantly more responsive to cash flow if the CEO displays overconfidence. In addition, we identify personal characteristics other than overconfidence (education, employment background, cohort, military service, and status in the company) that strongly affect the correlation between investment and cash flow. We are indebted to Brian Hall and David Yermack for providing us with the data. We are very grateful to Jeremy Stein for his invaluable support and comments. We also would like to thank Philippe Aghion, George

Does CEO overconfidence help to explain merger decisions? Overconfident CEOs overestimate their ability to generate returns. As a result, they overpay for target companies and undertake value-destroying mergers. The effects are strongest if they have access to internal financing. We test these predictions using two proxies for overconfidence: CEOs' personal overinvestment in their company and their press portrayal. We find that the odds of making an acquisition are 65 % higher if the CEO is classified as overconfident. The effect is largest if the merger is diversifying and does not require external financing. The market reaction at merger announcement (–90 basis points) is significantly more negative than for non-overconfident CEOs (–12 basis points). We consider alternative interpretations including inside information, signaling, and risk tolerance.

A longstanding controversy in economics and finance is whether financial markets are governed by rational forces or by emotional responses. We study the importance of emotion in the decisionmaking process of professional securities traders by measuring their physiological characteristics, e.g., skin conductance, blood volume pulse, etc., during live trading sessions while simultaneously capturing real-time prices from which market events can be detected. In a sample of 10 traders, we find statistically significant differences in mean electrodermal responses during transient market events relative to no-event control periods, and statistically significant mean changes in cardiovascular variables during periods of heightened market volatility relative to normal-volatility control periods. We also observe significant differences in these physiological response across the 10 traders which may be systematically related to the traders’ levels of experience.

The 30th anniversary of The Journal of Portfolio Management is a milestone in the rich intellectual history of modern finance, firmly establishing the relevance of quantitative models and scientific inquiry in the practice of financial management. One of the most enduring ideas from this intellectual history is the Efficient Markets Hypothesis (EMH), a deceptively simple notion that has become a lightning rod for its disciples and the proponents of behavioral economics and finance. In its purest form, the EMH obviates active portfolio management, calling into question the very motivation for portfolio research. It is only fitting that we revisit this groundbreaking idea after three very successful decades of this Journal. In this article, I review the current state of the controversy surrounding the EMH and propose a new perspective that reconciles the two opposing schools of thought. The proposed reconciliation, which I call the Adaptive Markets Hypothesis (AMH), is based on an evolutionary approach to economic interactions, as well as some recent research in the cognitive neurosciences that has been transforming and revitalizing the intersection of psychology and economics. Although some of these ideas have not yet been fully articulated within a rigorous quantitative framework, long time students of the EMH and seasoned practitioners will no doubt recognize immediately the possibilities generated by this new perspective. Only time will tell whether its potential will be fulfilled. I begin with a brief review of the classic version of the EMH, and then summarize the most significant criticisms leveled against it by psychologists and behavioral economists. I argue that the sources of this controversy can

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Our model of the initial public offering process links the three main empirical IPO ‘anomalies’ – underpricing, hot issue markets, and long-run underperformance – and traces them to a common source of inefficiency. We relate hot IPO markets (such as the 1999/2000 market for Internet IPOs) to the presence of a class of investors who are ‘irrational’ in the sense of having exuberant expectations regarding future performance. Underpricing and long-run underperformance emerge as underwriters attempt to maximize profits from the sale of equity, at the expense of these exuberant investors. Underpricing serves to compensate regular IPO investors for their role in restricting the supply of available shares and maintaining prices. The model is shown to be consistent with many aspects of the IPO process. It also generates a number of new empirical predictions.

The link between asset valuations and investor sentiment is the subject of considerable debate in the profession. We address this question by examining how survey data on investor sentiment relates to i) long-horizon returns, and ii) asset valuations. If excessive optimism drives prices above intrinsic values, periods of high sentiment should be followed by low returns as market prices revert to fundamental values. We find this to be the case for the overall stock market at horizons of two to three years. The relation is strongest for large-capitalization, low book-to-market (growth) portfolios. We also examine the relation between sentiment levels and deviations from intrinsic value. Using errors from an independent pricing model, we find sentiment is positively related to valuation errors using a variety of tests. All of our results are robust to the inclusion of other factors that have been shown to forecast stock returns, including past returns.

Research in behavioral corporate finance takes two distinct approaches. The first emphasizes that investors are less than fully rational. It views managerial financing and investment decisions as rational responses to securities market mispricing. The second approach emphasizes that managers are less than fully rational. It studies the effect of nonstandard preferences and judgmental biases on managerial decisions. This survey reviews the theory, empirical challenges, and current evidence pertaining to each approach. Overall, the behavioral approaches help to explain a number of important financing and investment patterns. The survey closes with a list of open questions.

The battle between proponents of the Efficient Markets Hypothesis and champions of behavioral finance has never been more pitched, and little consensus exists as to which side is winning or the implications for investment management and consulting. In this article, I review the case for and against the Efficient Markets Hypothesis and describe a new framework—the Adaptive Markets Hypothesis—in which the traditional models of modern financial economics can coexist alongside behavioral models in an intellectually consistent manner. Based on evolutionary principles, the Adaptive Markets Hypothesis implies that the degree of market efficiency is related to environmental factors characterizing market ecology such as the number of competitors in the market, the magnitude of profit opportunities available, and the adaptability of the market participants. Many of the examples that behavioralists cite as violations of rationality that are inconsistent with market efficiency—loss aversion, overconfidence, overreaction, mental accounting, and other behavioral biases—are, in fact, consistent with an evolutionary model of individuals adapting to a changing environment via simple heuristics. Despite the qualitative nature of this new paradigm, I show that the Adaptive Markets Hypothesis yields a number of surprisingly concrete applications for both investment managers and consultants.

∗This paper is an updated version of a previous working paper, “The Positive Role of Overconfidence and