Psychological versus economic models of bounded rationality

That the rationality of individual people is ‘bounded’ – that is, finite in scope and representational reach, and constrained by the opportunity cost of time – cannot reasonably be controversial as an empirical matter. In this context, the paper addresses the question as to why, if economics is an empirical science, economists introduce bounds on the rationality of agents in their models only grudgingly and partially. The answer defended in the paper is that most economists are interested primarily in markets and only secondarily in the dynamics of individual decisions – specifically, they are interested in these dynamics mainly insofar as they might systematically influence the most useful approaches to modeling interesting markets. In market contexts, bounds on rationality are typically generated by institutional and informational properties specific to the market in question, which arise and are sustained by structural dynamics that do not originate in or reduce to individuals' decisions or psychological dispositions. To be sure, these influences interact with psychological dispositions, so economists have reason to attend to the psychology of valuation. But no general model of bounded rationality should ever be expected to feature in the economist's toolkit, regardless of the extent to which psychologists successfully identify specific human cognitive limitations. Use of moderate rational expectations assumptions should be understood in this light. Such assumptions are readily relaxed in specific applications, and in ways customized to modeling circumstances, that modelers, experimentalists, and econometricians are making steadily more sophisticated.     

Bounded rationality: static versus dynamic approaches

Summary. Two kinds of theories of boundedly rational behavior are possible. Static theories focus on stationary behavior and do not include any explicit mechanism for temporal change. Dynamic theories, on the other hand, explicitly model the fine-grain adjustments made by the subjects in response to their recent experiences. The main contribution of this paper is to argue that the restrictions usually imposed on the distribution of choices in the static approach are generically not supported by a dynamic adjustment mechanism. The genericity here is understood both in the measure theoretic and in the topological sense.Received: 29 April 2002, Revised: 11 February 2004, JEL Classification Numbers: C0, D7.I thank Peter Bardsley and Rabee Tourky for useful suggestions. Special thanks are due to an anonymous referee.     

Investor sentiment,variance risk premium and delta-hedged gains

Delta-hedged gains are supposed to be negative and represent a volatility risk premium. Using a sample of Standard & Poor 500 index options from 2006 to 2009, this study documents two anomalies that cannot be explained by the volatility risk premium. First, delta-hedged gains are more negative for out-of-money options than for at-the-money options. Second, delta-hedged gains are significantly positive during financial crisis period. We propose a behavioural explanation in which both option prices and stock prices are affected by investor’s sentiment, but pessimistic sentiment has a greater impact on stock market than option market. This asymmetric response to pessimistic mood in turn affects the relative expensiveness of option prices.     

Monopolists and viscous demand

We characterize the optimal dynamic price policy of a monopolist who faces “viscous” demand for its services. Demand is viscous if it adjusts relatively slowly to price changes. We show that with the optimal policy the monopolist stops short of achieving 100% market penetration, even when all of the consumers have the same long-run willingness to pay for the service. Furthermore, for certain parameter values in the model, the price policy requires rapid oscillations of the price path.     

Investor sentiment,trading behavior and stock returns

This article examines how investor sentiment and trading behaviour affect asset returns. By analysing the unique stock trading dataset of the Korean market, we find that high investor sentiment induces higher stock market returns. We also find that institutional (individual) trades are positively (negatively) associated with stock returns, suggesting the information superiority (inferiority) of institutional (individual) investors. Investor sentiment generally plays a more important role in explaining stock market returns than investor trading behaviour.     

A non-linear approach for predicting stock returns and volatility with the use of investor sentiment indices

The popular sentiment-based investor index S^BW introduced by Baker and Wurgler (2006, 2007) is shown to have no predictive ability for stock returns. However, Huang et al. (2015) developed a new investor sentiment index, S^PLS, which can predict monthly stock returns based on a linear framework. However, the linear model may lead to misspecification and lack of robustness. We provide statistical evidence that the relationship between stock returns, S^BW and S^PLS is characterized by structural instability and inherent nonlinearity. Given this, using a nonparametric causality approach, we show that neither S^BW nor S^PLS predicts stock market returns or even its volatility, as opposed to previous empirical evidence.     

The importance of fear: investor sentiment and stock market returns

The presence of investor sentiment pushes asset prices away from the equilibrium level justified by underlying fundamentals. While sentiment is not directly observable, identifying appropriate proxies and, quantifying the impact of sentiment on asset prices is an important topic. Asset prices that do not appropriately reflect fundamental values may result in inefficient allocation of capital – impacting portfolio allocation decisions and the cost of capital. Utilizing a number of sentiment proxies, over the period 1990–2015, we demonstrate a strong relationship between investor sentiment and stock returns that is consistent with theoretical explanations of sentiment. We determine that implied volatility index (VIX) is the preferred measure of sentiment in terms of improving model fit and adding explanatory power. Causality tests suggest that investor fear (VIX) drives returns across firm-size and value, and also across industry. We also illustrate that firms that are more subjective to value, or face limits to arbitrage, such as small-cap stocks, or those in the business equipment (technology) or telecoms industry, are most responsive to changes investor sentiment. Finally, we demonstrate that sentiment has a greater influence on market returns during recession, when sentiment is at its lowest ebb, and this is particularly true for those stocks most susceptible to speculative demand.     

Skewness preferences,asset prices and investor sentiment

Prior research has found that investors have strong preferences for stocks with positive skewness. These preferences have been shown to lead to price premiums and subsequent underperformance. This study extends this growing body of literature by testing whether the underperformance of stocks with positive skewness is driven by periods of high investor sentiment. The motivation for these tests is based on a broad literature in Psychology that an individual’s mood can directly affect the individual’s subjective probability assessments. In the framework of our tests, more optimism among investors may strengthen investors’ skewness preferences. The empirical results in this study support this idea as the underperformance of positively skewed stocks is shown to be primarily driven by periods of high investor sentiment.     

Conservative belief and rationality

Playersʼ beliefs may be incompatible, in the sense that player i can assign probability 1 to an event E to which player j assigns probability 0. One way to block incompatibility is to assume a common prior. We consider here a different approach: we require playersʼ beliefs to be conservative, in the sense that all players must ascribe the actual world positive probability. We show that common conservative belief of rationality (CCBR) characterizes strategies in the support of a subjective correlated equilibrium where all playersʼ beliefs have common support. We also define a notion of strong rationalizability, and show that it is characterized by CCBR.     

The partially cursed and the analogy-based expectation equilibrium

Recent literature has established a link between the fully cursed equilibrium and the analogy-based expectation equilibrium. In this note, even the partially cursed equilibrium is shown to correspond to an analogy-based expectation equilibrium.     

Sampling equilibrium, with an application to strategic voting

We suggest an equilibrium concept for a strategic model with a large number of players in which each player observes the actions of only a small number of the other players. The concept fits well situations in which each player treats his sample as a prediction of the distribution of actions in the entire population, and responds optimally to this prediction. We apply the concept to a strategic voting model and investigate the conditions under which a centrist candidate can win the popular vote although his strength in the population is smaller than the strengths of the right and left candidates.     

Learning,forecasting and optimizing: An experimental study

Rational Expectations (RE) models have two crucial dimensions: (i) agents on average correctly forecast future prices given all available information, and (ii) given expectations, agents solve optimization problems and these solutions in turn determine actual price realizations. Experimental tests of such models typically focus on only one of these two dimensions. In this paper we consider both forecasting and optimization decisions in an experimental cobweb economy. We report results from four main experimental treatments: (1) subjects form forecasts only, (2) subjects determine quantity only (solve an optimization problem), (3) they do both and (4) they are paired in teams and one member is assigned the forecasting role while the other is assigned the optimization task. All treatments converge to Rational Expectation Equilibrium (REE), but at different speeds. We observe that performance is the best in treatment 1 and the worst in Treatment 3. We further find that most subjects use adaptive rules to forecast prices. Given a price forecast, subjects are less likely to make conditionally optimal production decisions in Treatment 3 where the forecast is made by themselves, than in Treatment 4 where the forecast is made by the other member of their team, which suggests that “two heads are better than one” in term of the speed of finding the REE.     

Welfare economics and bounded rationality: the case for model-based approaches

In this paper, we examine the problems facing a policy maker who observes inconsistent choices made by agents who are boundedly rational. We contrast a model-less and a model-based approach to welfare economics. We make the case for the model-based approach and examine its advantages as well as some problematic issues associated with it.     

Learning by trial and error

A person learns by trial and error if he occasionally tries out new strategies, rejecting choices that are erroneous in the sense that they do not lead to higher payoffs. In a game, however, strategies can become erroneous due to a change of behavior by someone else. We introduce a learning rule in which behavior is conditional on whether a player experiences an error of the first or second type. This rule, called interactive trial and error learning, implements Nash equilibrium behavior in any game with generic payoffs and at least one pure Nash equilibrium.     

Market clearing and derivative pricing

Summary. We develop a method of assigning unique prices to derivative securities, including options, in the continuous-time finance model developed in Raimondo (2001). In contrast with the martingale method of valuing options, which cannot distinguish among infinitely many possible option pricing processes for a given underlying securities price process when markets are dynamically incomplete, our option prices are uniquely determined in equilibrium in closed form as a function of the underlying economic data.Received: 14 April 2003, Revised: 7 January 2004, JEL Classification Numbers: G13, D52.This paper is dedicated to Birgit Grodal, whose strength and character we greatly admire. We are very grateful to Darrell Duffie, Steve Evans, Botond Koszegi, Roger Purves, Jacob Sagi, Chris Shannon, Bill Zame and an anonymous refereee for very helpful discussions and comments. The work of both authors was supported by Grant SES-9710424, and Andersons work was supported by Grant SES-0214164, from the National Science Foundation.     

A cognition paradigm clash: Simon,situated cognition and the interpretation of bounded rationality

Simon’s notion of bounded rationality is deeply intertwined with his activity as a cognitive psychologist and founder of so-called cognitivism, a mainstream approach in cognitive psychology until the 1980s. Cognitivism, understood as ‘symbolic information processing,’ provided the first cognitive psychology foundation to bounded rationality. Has bounded rationality since then fully followed the development of cognitive psychology beyond symbolic information processing in the post-Simonian era? To answer this question, this paper focuses on Simon’s opposition during the 1990s to a new (paradigmatic) view of cognition called situated cognition, which has since put into question the entire view in cognitive psychology of humans as symbolic information processors. This paper then reads the cognitivism/situated cognition debate through the lens of current bounded rationality research in economics, in order (i) to inquire into whether it has tackled the issues in that controversy; (ii) to envisage possible new foundations for a cognitive psychology-based bounded rationality.     

The impacts of investor sentiment and price uncertainty on the effects of open-market share repurchase announcements

This study probes into relationship between investor sentiment and cumulative abnormal returns (CAR) of share repurchase announcements, and it treats market return as threshold variable. By threshold regression model, it tries to find the effect of market situations on relation between investor sentiment and CAR. According to empirical result, in share market of Taiwan, investor sentiment can explain CAR. When share market is extremely pessimistic (market return lower than ?16.0053%), relation between investor sentiment and CAR will change to some degree. In addition, relation between price risk of announcement company and CAR will disappear with the extremely pessimistic situation of market.     

Rational expectations,difference of opinions and asset pricing

This article applies the concept of relative overconfidence (the measure of how heavily investors depend on others’ information) to combine the rational expectations equilibrium (REE) and difference of opinions (DO) models. And we discuss the effects of relative overconfidence on asset price efficiency and trading volume. We find that when investors hold assets to maturity, relative overconfidence has no effect on price efficiency and trading volume; however, when investors speculate, relative overconfidence reduces price informativeness and trading volume, because investors will reckon asset prices as more noisy and find it meaningless to speculate on capital gains based on their private information. Our results highlight the role of speculation in differentiating REE and DO models and influencing the effects of overconfidence.     

Policy Consequences of Multiple Equilibria and the Indeterminacy of Economic Outcomes in a Boundedly Rational World: Closing the System with Non-Economic Variables1

In the conventional economic wisdom, the notion of unique equilibria that are efficient and Pareto optimal dominates the modeling discourse. Hebert Simon proposed an alternative analytical framework where the notion of multiple and sustainable equilibria is critical. Multiple equilibrium is the crucial stylized fact of economic life that requires better understanding and modeling. Of particular significance, Simon touched on the importance of institutions and differential power relationships in affecting economic outcomes. But this modeling approach was not well developed by Simon. Following from his contributions, further develop the notion of multiple equilibria especially in the realm of production with an emphasis on x-efficiency theory. I bring to bear the importance of institutional parameters (including power relationships), culture, norms, ethics, and moral sentiments to the determination of economic outcomes. In the model developed here, boundedly rational decision-makers’ choices are contextualized and constrained by complex environmental factors. No one choice is either inevitable or economically efficient. A multiplicity of outcomes is possible and sustainable inclusive of those that are suboptimal. Much depends on individual preferences and institutional design. This has significant implication for institutional design and policy.     

Stability,sequential rationality,and subgame consistency

In this paper we analyze dynamic strategic behavior by means of the idea of "stability." We develop a solution concept of "sequentially stable equilibrium (SSE)" that satisfies subgame consistency. All SSEs are characterized by the largest stable set that yields exactly all the backward induction outcomes. We also provide a refinement of the SSE. We compare the SSE and its refinement with some existing solution concepts in the literature We are grateful to the editor and two anonymous referees for very useful comments and suggestions that led to this revision. We thank Chih Chang, Yi-Chun Chen, Chenying Huang, Huiwen Koo, Man-Chung Ng, Shyh-fang Ueng, and Chun-Hsien Yeh for helpful comments and discussions. We also thank participants in seminars at Academia Sinica, National Dong Hwa University, and the Third Pan-Pacific Game Theory Conference. Financial support from the Social Sciences and Humanities Research Council of Canada (SSHRC), the National Science Council of Taiwan, and the Economic and Social Research Council of the UK is gratefully acknowledged. The usual disclaimer applies.