[We develop a model for an investor with multiple priors and aversion to ambiguity. We characterize the multiple priors by a "confidence interval" around the estimated expected returns and we model ambiguity aversion via a minimization over the priors. Our model has several attractive features: (1) it has a solid axiomatic foundation; (2) it is flexible enough to allow for different degrees of uncertainty about expected returns for various subsets of assets and also about the return-generating model; and (3) it delivers closed-form expressions for the optimal portfolio. Our empirical analysis suggests that, compared with portfolios from classical and Bayesian models, ambiguity-averse portfolios are more stable over time and deliver a higher out-of sample Sharpe ratio.]

This article studies the asset pricing implication of imprecise knowledge about rare events. Modeling rare events as jumps in the aggregate endowment, we explicitly solve the equilibrium asset prices in a pure-exchange economy with a representative agent who is averse not only to risk but also to model uncertainty with respect to rare events. The equilibrium equity premium has three components: the diffusive- and jump-risk premiums, both driven by risk aversion; and the "rare-event premium," driven exclusively by uncertainty aversion. To disentangle the rare-event premiums from the standard risk-based premiums, we examine the equilibrium prices of options across moneyness or, equivalently, across varying sensitivities to rare events. We find that uncertainty aversion toward rare events plays an important role in explaining the pricing differentials among options across moneyness, particularly the prevalent "smirk" patterns documented in the index options market.

[When the market is incomplete, a new non-redundant derivative security cannot be priced by no-arbitrage arguments alone. Moreover, there will be a multiplicity of stochastic discount factors and each of them may give a different price for the new derivative security. This paper develops an approach to the selection of a stochastic discount factor for pricing a new derivative security. The approach is based on the idea that the price of a derivative security should not vary too much when the payoff of the primitive security is slightly perturbed, i.e., the price of the derivative should be robust to model misspecification. The paper develops two metrics of robustness. The first is based on robustness in expectation. The second is based on robustness in probability and draws on tools from the theory of large deviations. We show that in a stochastic volatility model, the two metrics yield analytically tractable bounds for the derivative price, as the underlying stochastic volatility model is perturbed. The bounds can be readily used for numerical examination of the sensitivity of the price of the derivative to model misspecification.]

We demonstrate that limited participation can arise endogenously in the presence of model uncertainty and heterogeneous uncertainty-averse investors. When uncertainty dispersion among investors is small, full participation prevails in equilibrium. Equity premium is related to the average uncertainty among investors and a conglomerate trades at a price equal to the sum of its single-segment components. When uncertainty dispersion is large, investors with high uncertainty choose not to participate in the stock market, resulting in limited market participation. When limited participation occurs, participation rate and equity premium can decrease in uncertainty dispersion and a conglomerate trades at a discount.

[We study the share privatization process in China to investigate whether and how the removal of market frictions is associated with efficiency gains. Prior to the reform, domestic A-shares were divided into tradable and non-tradable shares. As a result of the reform, holders of non-tradable shares compensated holders of tradable shares in order to make their shares tradable. We show that size is positively associated with both the gain in risk sharing and the price impact of more shares coming on the market as a result of the reform. Our study highlights the role of risk sharing in China's share issue privatization process.]

[In conformity with the Savage model of decision-making, modern asset pricing theory assumes that agents' beliefs about the likelihoods of future states of the world may be represented by a probability measure. As a result, no meaningful distinction is allowed between risk, where probabilities are available to guide choice, and uncertainty, where information is too imprecise to be summarized adequately by probabilities. In contrast, Knight and Keynes emphasized the distinction between risk and uncertainty and argued that uncertainty is more common in economic decision-making. Moreover, the Savage model is contradicted by evidence, such as the Ellsberg Paradox, that people prefer to act on known rather than unknown or vague probabilities. This paper provides a formal model of asset price determination in which Knightian uncertainty plays a role. Specifically, we extend the Lucas (1978) general equilibrium pure exchange economy by suitably generalizing the representation of beliefs along the lines suggested by Gilboa and Schmeidler. Two principal results are the proof of existence of equilibrium and the characterization of equilibrium prices by an "Euler inequality." A noteworthy feature of the model is that uncertainty may lead to equilibria that are indeterminate, that is, there may exist a continuum of equilibria for given fundamentals. That leaves the determination of a particular equilibrium price process to "animal spirits" and sizable volatility may result. Finally, it is argued that empirical investigation of our model is potentially fruitful.]

We investigate an asset pricing model with preferences cycling between high risk aversion and low EIS in fall/winter and the reverse in spring/summer. Calibrating to consumption data and allowing plausible preference parameter values, we produce returns that match observed equity and Treasury returns across the seasons: risky returns are higher and risk-free returns are lower or stable in fall/winter, and they reverse in spring/summer. Further, risky returns vary more than risk-free returns. A novel finding is that both EIS and risk aversion must vary seasonally to match observed returns. Further, the degree of necessary seasonal change in EIS is small. (JEL E44, G11, G12)

This paper constructs a space of states of the world representing the exhaustive uncertainty facing each player in a strategic situation. The innovation is that preferences are restricted primarily by 'regularity' conditions and need not conform with subjective expected utility theory. The construction employs a hierarchy of preferences, rather than of beliefs as in the standard Bayesian model. Applications include the provision of foundations for a Harsanyi-style game of incomplete information and a rich framework for the axiomatization of solution concepts for complete information normal form games. Copyright 1996 by The Econometric Society.

This study investigates how accounting harmonization affects one particular group of financial statement users—financial analysts. We find that mandatory International Financial Reporting Standards (IFRS) adoption attracts foreign analysts, particularly those from countries that are simultaneously adopting IFRS along with the covered firm's country and those with prior IFRS experience. We also find that mandatory IFRS adoption improves foreign analysts’ forecast accuracy. The change in analyst following increases with the distance between prior local Generally Accepted Accounting Principles (GAAP) and IFRS and with the extent to which IFRS adoption eliminates GAAP differences between the firm's country and the analyst's country. IFRS adoption also attracts more local analysts, particularly those with prior IFRS experience and with an international portfolio prior to mandated IFRS adoption in their home country. Local analysts’ forecast accuracy is not affected by IFRS adoption. Overall, our results suggest that accounting harmonization brings comparability benefits that enhance the usefulness of accounting data.