This paper provides evidence that free riders are heavily punished even if punishment is costly and does not provide any material benefits for the punisher. The more free riders negatively deviate from the group standard the more they are punished. As a consequence, the existence of an opportunity for costly punishment causes a large increase in cooperation levels because potential free riders face a credible threat. We show, in particular, that in the presence of a costly punishment opportunity almost complete cooperation can be achieved and maintained although, under the standard assumptions of rationality and selfishness, there should be no cooperation at all. We also show that free riding causes strong negative emotions among cooperators. The intensity of these emotions is the stronger the more the free riders deviate from the group standard. Our results provide, therefore, support for the hypothesis that emotions are guarantors of credible threats.

Happiness is generally considered to be an ultimate goal in life; virtually everybody wants to be happy. The United States Declaration of Independence of 1776 takes it as a self-evident truth that the “pursuit of happiness” is an “unalienable right”, comparable to life and liberty. It follows that economics is – or should be – about individual happiness. In particular, the question is how do economic growth, unemployment and inflation, as well as institutional factors such as good governance, affect individual well-being? In addition to this intrinsic interest, there are three major reasons for economists to consider happiness. The first is economic policy. At the micro-level, it is often impossible to make a Pareto-optimal proposal, because a social action entails costs for some individuals. Hence an evaluation of the net effects, in terms of individual utilities, is needed. On an aggregate level, economic policy must deal with trade-offs, especially those between unemployment and

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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

The standard economic model of decision making assumes a decision maker makes her choices to maximize her utility or happiness. Her current emotional state is not explicitly considered. Yet there is a large psychological literature that shows that current emotional state, in particular positive affect, has a significant effect on decision making. This paper offers a way to incorporate this insight from psychology into economic modeling. Moreover, this paper shows that this simple insight can parsimoniously explain a wide variety of behaviors.

We investigate several possible links between psychological factors and trading performance in a sample of 80 anonymous day-traders. Using daily emotional-state surveys over a fiveweek period as well as personality inventory surveys, we construct measures of personality traits and emotional states for each subject and correlate these measures with daily normalized profits-and-losses records. We find that subjects whose emotional reaction to monetary gains and losses was more intense on both the positive and negative side exhibited significantly worse trading performance. Psychological traits derived from a standardized personality inventory survey do not reveal any specific “trader personality profile”, raising the possibility that trading skills may not necessarily be innate, and that different personality types may be able to perform trading functions equally well after proper instruction and practice.

We test the effect of players ’ moods on their behavior in a gift-exchange game. In the first stage of the game, player 1 chooses a transfer to player 2. In the second stage, player 2 chooses an effort level. Higher effort is more costly for player 2, but it increases player 1’s payoff. We say that player 2 reciprocates if effort is increasing in the transfer received. Player 2 is generous if effort is incurred regardless of the transfer received. Subjects play this game in two different moods. To induce a ‘bad mood’, subjects in the role of player 2 watched a sad movie before playing the game; to induce a ‘good mood’, they watched a funny movie. Mood induction was effective: subjects who saw the funny movie reported a significantly better mood than those who saw the sad movie. These two moods lead to significant differences in player 2’s behavior. We find that a bad mood implies more reciprocity while a good mood implies more generosity. Since high transfers are relatively more common, player 1 make more money when second movers are in a bad mood.

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.

The motivation of decision makers who care for emotions, reciprocity, or social conformity may depend directly on beliefs (about choices, beliefs, or information). Geanakoplos, Pearce & Stacchetti (Games and Economic Behavior, 1989) point out that traditional game theory is ill-equipped to address such matters, and they pioneer a new framework which does. However, their toolbox — psychological game theory — incorporates several restrictions that rule out plausible forms of belief-dependent motivation. Building on recent work on dynamic interactive epistemology, we propose a more general framework. Updated higher-order beliefs, beliefs of others, and plans of action may influence motivation, and we can capture dynamic psychological effects (such as sequential reciprocity, psychological forward induction, regret, and anxiety) that were previously ruled out. We develop solution concepts, provide examples, and explore properties.

The efficient markets hypothesis (EMH) maintains that market prices fully reflect all available information. Developed independently by Paul A. Samuelson and Eugene F. Fama in the 1960s, this idea has been applied extensively to theoretical models and empirical studies of financial securities prices, generating considerable controversy as well as fundamental insights into the price-discovery process. The most enduring critique comes from psychologists and behavioural economists who argue that the EMH is based on counterfactual assumptions regarding human behaviour, that is, rationality. Recent advances in evolutionary psychology and the cognitive neurosciences may be able to reconcile the EMH with behavioural anomalies.