information acquisition and under diversification if an investor wants to form a portfolio of risky assets and can exert effort to collect information on the future value of these assets before he invests which assets should he learn about the best assets to acquire information about are ones the investor expects to hold but the assets the investor holds depend on the information he observes we build a framework to solve jointly for investment and information choices with general preferences and information cost functions although the optimal research strategies depend on preferences and costs the main result is that the investor who can first collect information systematically deviates from holding a diversified portfolio information acquisition can rationalize investing in a diversified fund and a concentrated set of assets an allocation often observed but usually deemed anomalous copyright wiley blackwell

on the mis measurement of legislator ideology and shirking in this paper we show that current statistical measures of legislator s shirking are implicitly based on the electoral concept of a unique majority rule equilibrium point in the policy space where elections are contested we note that such equilibria do not exist generically and present statistical results showing that cross sectional regressions where legislators voting indices are predicted by district average demograhic and economic data are mis specified we also discuss a weaker equilibrium construct the uncovered set and present statistical evidence showing that differences in voting behavior between senators from the same state are positively related to the heterogeneity of the electorate we argue that current evidence alleged to show shirking by senators is equally consistent with senators who perfectly represent an idiosyncratic constituency that cannot be represented by district average data

speculation under unawareness no trade theorems establish that in various trading environments investors who share a common prior will not engage in speculation as long as expected utility bayesian updating and full awareness are imposed we relax the last assumption by allowing for asymmetric unawareness and examine under which conditions speculative behaviour emerges we find that if common knowledge is assumed as in the settings of aumann 1976 and milgrom and stokey 1982 unawareness cannot generate speculation this is not true however in settings where no common knowledge is assumed such as speculation in equilibrium geanakoplos 1989 and betting that is always beneficial morris 1994 unless stronger conditions on awareness are imposed

delegated portfolio management abstract a problem of screening agents with privately known forecasting abilities and reservation utilities and then eliciting truthful information from these agents once they are employed is considered for the case of risk averse agents and large principals an approximately optimal solution is constructively characterized under the assumption that payoffs are normally distributed a significant extension of the definnetti savage probability elicitation result is developed under this extension knowledge of agent preferences is not required when the underlying conditional distributions are symmetric and this fact is exploited to solve the screening problem in a mean variance formulation

does market incompleteness matter this paper argues that incompleteness of intertemporal financial markets has little effect on welfare prices or consumption in an economy with a single consumption good provided that traders are long lived and patient a riskless bond is traded shocks are transitory and there is no aggregate risk in an economy with aggregate risk a similar conclusion holds provided traders share the same crra utility function and the right assets are traded examples demonstrate that these conclusions need not hold if the wrong assets are traded or if the economy has multiple consumption goods

prudence with respect to ambiguity under expected utility prudence is equivalent to a positive third derivative of utility and plays a crucial role in precautionary saving behaviour eeckhoudt and schlesinger 2006 proposed behavioural definitions of prudence and of higher order risk preferences the present paper proposes a similar definition for prudence with respect to ambiguity i e situations in which objective probabilities are not available implications for several ambiguity models are derived ambiguity prudence is implied by hansen and sargent s 2001 multiplier preferences empirically correlates with financial behaviour and plays a key role in prevention behaviour this article is protected by copyright all rights reserved

uncertainty and risk in financial markets this paper considers a general equilibrium model in which the distinction between uncertainty and risk is formalized by assuming agents have incomplete preferences over statecontingent consumption bundles as in bewley 1986 without completeness individual decision making depends on a set of probability distributions over the state space a bundle is preferred to another if and only if it has larger expected utility for all probabilities in this set when preferences are complete this set is a singleton and the model reduces to standard expected utility in this setting we characterize pareto optima and equilibria and show that the presence of uncertainty generates robust indeterminacies in equilibrium prices and allocations for any specification of initial endowments we derive comparative statics results linking the degree of uncertainty with changes in equilibria despite the presence of robust indeterminacies we show that equilibrium prices and allocations vary continuously with underlying fundamentals equilibria in a standard risk economy are thus robust to adding small degrees of uncertainty finally we give conditions under which some assets are not traded due to uncertainty aversion

knightian uncertainty and moral hazard abstract this paper presents a principal agent model in which the agent has imprecise beliefs we model this situation formally by assuming the agent s preferences are incomplete as in bewley 1986 2 in this setting incentives must be robust to knightian uncertainty we study the implications of robustness for the form of the resulting optimal contracts we give conditions under which there is a unique optimal contract and show that it must have a simple flat payment plus bonus structure that is output levels are divided into two sets and the optimal contract pays the same wage for all output levels in each set we derive this result for the case in which the agent s utility function is linear and then show it also holds if this utility function has some limited curvature

a characterization of ramsey equilibrium abstract consider a perfect foresight equilibrium model with a single capital good a borrowing constraint and many infinitely lived households with fixed but different discount factors the steady state capital stock is held by the most patient household quart j econ 95 1980 375 382 econ j 38 1928 543 559 an example shows the total capital can exhibit an equilibrium cycle in contrast to the stability property of the one household case in the example only the most patient household saves and his income deceases in capital we give a condition implying income is increasing in capital and use it to show any equilibrium converges to the steady state

financial complexity and trade what are the implications on trading activity if investors are not sophisticated enough to understand and evaluate trades that have a complex payoff structure can frictions generated by this type of financial complexity be so severe that they lead to a complete market freeze like that of the recent financial crisis starting from an allocation that is not pareto optimal we find that whether complexity impedes trade depends on how investors perceive risk and uncertainty for smooth convex preferences such as subjective expected utility complexity cannot halt trade even in the extreme case where each investor is so unsophisticated that he can only trade up to one arrow debreu security without being able to combine two or more in order to construct a complex trade however for non smooth preferences which allow for kinked indifference curves such as maxmin expected utility complexity can completely shut down trade

on existence and uniqueness of equilibrium in a class of noisy rational expectations models i study a general class of noisy rational expectations models that nests the standard grossman and stiglitz 1980 and hellwig 1980 models but relaxes the usual assumption of joint normality of asset pay offs and supply and allows for more general signal structures i provide a constructive proof of existence of equilibrium characterize the price function and provide sufficient conditions for uniqueness within the class of equilibria with continuous price functions which are met by both the grossman and stiglitz 1980 models and the hellwig 1980 models with a continuum of investors my solution approach does not rely on the typical conjecture and verify method and i exhibit a number of non normal examples in which asset prices can be characterized explicitly and in a closed form the results presented here open up a broad class of models for applied work to illustrate the usefulness of generalizing the standard model i show that in settings with non normally distributed pay offs shocks to fundamentals may be amplified purely due to learning effects price drifts can arise naturally and the disagreement return relation depends in a novel way on return skewness

first order and second order ambiguity aversion different models of uncertainty aversion imply strikingly different economic behavior the key to understanding these differences lies in the dichotomy between first order and second order ambiguity aversion which i define here my definition and its characterization are independent of specific representations of decisions under uncertainty i show that with second order ambiguity aversion a positive exposure to ambiguity is optimal if and only if there is a subjective belief such that the act s expected outcome is positive with first order ambiguity aversion zero exposure to ambiguity can be optimal examples in finance insurance and contracting demonstrate the economic relevance of this dichotomy this paper was accepted by han bleichrodt decision analysis

asymmetric information and the lack of portfolio diversification there is pervasive evidence that individuals invest primarily in local stocks and thus hold poorly diversified portfolios the present article develops a theoretical model in which the presence of informational asymmetries introduces home equity bias the main departure from previous theoretical work is the assumption that local investors outperform nonlocal investors in identifying the correct ranking of local investment opportunities instead of possessing superior information about the aggregate performance of the local stock market the second key assumption is based on the evidence that short selling is a costly activity

aggregation of heterogeneous time preferences we examine an economy whose consumers have different discount factors for utility possibly not exponential we characterize the properties of efficient allocations of resources and of the shadow prices that would decentralize such allocations we show in particular that the representative agent has a decreasing discount rate when as is usually posited all of a group s members have a constant discount rate and decreasing absolute risk aversion preferences we also identify conditions that lead the representative agent to have a rate of impatience that decreases with gross domestic product per capita

time varying fund manager skill we propose a new definition of skill as general cognitive ability to pick stocks or time the market we find evidence for stock picking in booms and market timing in recessions moreover the same fund managers that pick stocks well in expansions also time the market well in recessions these fund managers significantly outperform other funds and passive benchmarks our results suggest a new measure of managerial ability that weighs a fund s market timing more in recessions and stock picking more in booms the measure displays more persistence than either market timing or stock picking alone and predicts fund performance

pareto optima and equilibria when preferences are incompletely known an exchange economy in which agents have convex incomplete preferences defined by families of concave utility functions is considered sufficient conditions for the set of efficient allocations and equilibria to coincide with the set of efficient allocations and equilibria that result when each agent has a utility in her family are provided welfare theorems in an incomplete preferences framework therefore hold under these conditions and efficient allocations and equilibria are characterized by first order conditions

intertemporal equilibria with knightian uncertainty we study a dynamic and infinite dimensional model with incomplete multiple prior preferences in interior efficient allocations agents share a common risk adjusted prior and subjective interest rate interior efficient allocations and equilibria coincide with those of economies with subjective expected utility and priors from the agents multiple prior sets a specific model with neither risk nor uncertainty at the aggregate level is considered risk is always fully insured for small levels of ambiguity there exists an equilibrium with inertia where agents also insure fully against knightian uncertainty when the level of ambiguity exceeds a critical threshold full insurance no longer prevails and there exist equilibria with inertia where agents do not insure against uncertainty at all we also show that equilibria with inertia are indeterminate

interim efficient allocations under uncertainty abstract this paper considers an exchange economy under uncertainty with asymmetric information uncertainty is represented by multiple priors and posteriors of agents who have either bewley s incomplete preferences or gilboa schmeidler s maximin expected utility preferences the main results characterize interim efficient allocations under uncertainty that is they provide conditions on the sets of posteriors thus implicitly on the way how agents update the sets of priors for non existence of a trade which makes all agents better off at any realization of private information for agents with the incomplete preferences the condition is necessary and sufficient but for agents with the maximin expected utility preferences the condition is sufficient only a couple of necessary conditions for the latter case are provided

the dynamics of efficient asset trading with heterogeneous beliefs this paper analyzes the dynamic properties of portfolios that sustain dynamically complete markets equilibrium when agents have heterogeneous priors we argue that the conventional wisdom that belief heterogeneity generates continuous trade and significant fluctuations in individual portfolios may be correct but it needs some qualifications we consider an infinite horizon stochastic endowment economy populated by many bayesian agents with heterogeneous priors over the stochastic process of the states of nature our approach hinges on studying the portfolios that decentralize pareto optimal allocations since these allocations are typically history dependent we propose a methodology to provide a complete recursive characterization when agents believe that the process of states of nature is i i d but disagree about the probability of the states we show that even though heterogeneous priors within that class can indeed generate genuine changes in the portfolios of any dynamically complete markets equilibrium these changes vanish with probability one if the true process consists of i i d draws from a common distribution and the support of some agent s prior belief contains the true distribution finally we provide examples in which asset trading does not vanish because either i no agent learns the true conditional probability of the states or ii some agent does not know the true process generating the data is i i d

differential information and performance measurement using a security market line an uninformed observer using the tools of mean variance and security market line analysis to measure the performance of a portfolio manager who has superior information is unlikely to be able to make any reliable inferences while some positive results of a very limited nature are possible e g when there is a riskless asset or when information is restricted to be security specific in general anything is possible in particular a manager with superior information can appear to the observer to be below or above the security market line and inside or outside of the mean variance efficient frontier and any combination of these is possible mean variance theory predicts that if we plot expected returns against beta coefficients all securities plot on a single line known as the security market line sml since fpi the beta coefficient for security i is interpreted as a measure of the riskiness of security i the market line is a graphical representation of the linear relationship between risk and return what are we to make of deviations from the sml i e of securities or managed portfolios that do not plot on such a line if we can retain our intuitive interpretation of fj as the riskiness of asset i and the market line as the appropriate expected return needed to reward agents taking on various degrees of risk then vertical deviations from the market line represent abnormal returns that differ from what is merited this paper and the companion piece dybvig and ross 10 explore in detail the validity of this intuition and the question of what sml deviations really measure the companion piece analyzes sml deviations caused by the choice of an inefficient market or reference portfolio in this paper we analyze sml deviations caused by superior performance based on superior information the intuitive explanation of deviations from the sml has motivated many

check bouncing and fiscal irresponsibility evidence of nonideological shirking by legislators kalt and zupan have measured ideological shirking by legislators here we present evidence concerning nonideological shirking we demonstrate that representatives with more overdrawn checks tend to be more fiscally irresponsible with fiscal irresponsibility measured by national taxpayer union ratings and by representatives voting behavior on the recent house balanced budget amendment vote

model misspecification and underdiversification in this paper we study intertemporal portfolio choice when an investor accounts explicitly for model misspecification we develop a framework that allows for ambiguity about not just the joint distribution of returns for all stocks in the portfolio but also for different levels of ambiguity for the marginal distribution of returns for any subset of these stocks we find that when the overall ambiguity about the joint distribution of returns is high then small differences in ambiguity for the marginal return distribution will result in a portfolio that is significantly underdiversified relative to the standard mean variance portfolio

time patience and specialization patterns in the presence of asset trade specialization patterns in an open economy two sector growth model with endogenous capital accumulation are examined in the presence of free international lending and borrowing without free international lending and borrowing it is known that whereas the less time patient country decumulates real capital the more patient country accumulates real capital and eventually specializes in a capital intensive industry however free trade of international financial assets causes a dramatic change in long run specialization patterns in this case the less patient country may well specialize in the capital intensive industry and the more patient country in the labor intensive industry

sharing risk and ambiguity we study the market implications of ambiguity in common models we show that generic determinacy is a robust feature in general equilibrium models that allow a distinction between ambiguity and risk

non existence of recursive equilibria on compact state spaces when markets are incomplete abstract this paper analyzes one good exchange economies with two infinitely lived agents and incomplete markets it is shown that there are no recursive markov equilibria for which borrowing debt constraints never bind if the state space of exogenous and endogenous variables is a compact subset of r n moreover for large enough but finite borrowing limits no recursive equilibrium with compact state space exists these non existence results hold for any economy satisfying the following standard assumptions preferences are additively separable across time and states the one period utility function is time and state independent and unbounded from below endowments are bounded and follow a markov chain with stationary transition matrix there is some idiosyncratic risk and no aggregate risk

measuring investment performance in a rational expectations equilibrium model much research has been concerned with evaluating the performance of managed portfolios e g mutual funds and examining whether portfolio managers display in some sense superior performance superior performance would seemingly turn on the possession of superior information that is utilized in managing portfolios in general a fund s asset holdings or portfolio weights might not be observable to an outsider whether they are or not however they are likely to change over time this happens especially when better performance is a result of superior information since managers will change their portfolio composition on obtaining private information since such changes must be taken into account the problem of measuring performance of managed portfolios is inherently different from that of evaluating the performance of individual assets groups of assets or generally portfolios with constant and known composition

portfolio performance evaluation old issues and new insights this article presents a model that provides insights about various measures of portfolio performance the model explores several criticisms of these measures these include the problem of identifying an appropriate benchmark portfolio the possibility of overestimating risk because of market timing ability and the failure of informed investors to earn positive risk adjusted returns because of increasing risk aversion the article argues that these need not be serious impediments to performance evaluation

introduction to a general equilibrium approach to economic growth abstract endogenous growth theory has had some success in explaining the observed data related to the process of economic growth however the results of the models in this literature are typically very sensitive to their micro economic structure it is therefore important to understand how the growth process behaves under more general specifications of such features as the number of commodities the number and preferences of consumers the factors of production and the financial and information structures in other words valuable insights can be gained by integrating growth theory into the framework of general equilibrium theory the summary of the papers in this volume focuses on seven issues that are crucial to this integration and highlights the contributions of the papers to the resolution of these issues journal of economic literature classification numbers c61 d50 d90 f43 o30 o41

stationary ramsey equilibria under uncertainty abstract deterministic dynamic equilibrium models with borrowing constraints and heterogeneous agents exhibit stationary solutions where the most patient household owns the economy s capital stock an example shows that this result does not carry over to stationary stochastic environments we prove under some conditions the existence of a stationary rational expectations equilibrium in two related setups the first is the existence of a stationary nash equilibrium where each agent s payoff depends on his capital process and the capital processes of the remaining agents the second existence theorem applies to a stationary competitive equilibrium model journal of economic literatureclassification numbers e13 e21 d80

infinite horizon incomplete markets the model of general equilibrium with incomplete markets is a generalization of the arrow debreu model which provides a rich framework for studying problems of macroeconomics this paper shows how the model which has so far been restricted to economies with a finite horizon can be extended to the more natural setting of an open ended future thereby providing an extension of the finite horizon representative agent models of modern macroeconomics to economies with heterogeneous agents and incomplete markets there are two natural concepts of equilibrium over an infinite horizon which prevent agents from entering into ponzi schemes that is from indefinitely postponing the repayment of their debts the first is based on debt constraints which place bounds on debt at each date event the second is based on transversality conditions which limit the asymptotic rate of growth of debt the concept of an equilibrium with debt constraint is a natural concept of equilibrium for macroeconomic analysis however the concept of an equilibrium with transversality condition is more amenable to theoretical analysis since it permits the powerful techniques of arrow debreu theory to be carried over to the setting of incomplete markets in an economy in which agents are impatient expressed by the mackey continuity of their preference orderings and have a degree of impatience at each date event which is bounded below a concept defined in the paper we show that the equilibria of an economy with transversality condition coincide with the equilibria with debt constraints an equilibrium with transversality condition is shown to exist it follows that for each economy there is an explicit bound m such that an equilibrium with explicit debt constraint m exists in which the constraint is never binding this latter property ensuring that the debt constraint whose objective is to prevent ponzi schemes does not in itself introduce a new imperfection into the model over and above the incompleteness of the markets

overlapping risk adjusted sets of priors and the existence of efficient allocations and equilibria with short selling the theory of existence of equilibrium with short selling is reconsidered under risk and ambiguity modelled by risk averse variational preferences no arbitrage conditions are given in terms of risk adjusted priors a sufficient condition for existence of efficient allocations is the overlapping of the interiors of the risk adjusted sets of priors or the inexistence of mutually compatible trades with non negative expectation with respect to any risk adjusted prior these conditions are necessary when agents are not risk neutral at extreme levels of wealths it is shown that the more uncertainty averse or risk averse the agents the more likely are efficient allocations and equilibria to exist

information immobility and the home bias puzzle many argue that home bias arises because home investors can predict home asset payoffs more accurately than foreigners can but why does global information access not eliminate this asymmetry we model investors endowed with a small home information advantage who choose what information to learn before they invest surprisingly even when home investors can learn what foreigners know they choose not to investors profit more from knowing information others do not know learning amplifies information asymmetry the model matches patterns of local and industry bias foreign investments portfolio outperformance and asset prices finally we propose new avenues for empirical research

a theory of anticipated utility abstract a new theory of cardinal utility with an associated set of axioms is presented it is a generalization of the von neumann morgenstern expected utility theory which permits the analysis of phenomena associated with the distortion of subjective probability

rational asset pricing bubbles this paper provides a fairly systematic study of general economic conditions under which rational asset pricing bubbles may arise in an intertemporal competitive equilibrium framework our main results are concerned with nonexistence of asset pricing bubbles in those economies these results imply that the conditions under which bubbles are possible including some well known examples of monetary equilibria are relatively fragile this paper is concerned with the conditions under which asset prices in an intertemporal competitive equilibrium are equal to the present value of the streams of future dividends to which each asset represents a claim according to a central result of the theory of finance this is very generally true in the case of economies with trading at only a finite sequence of dates as long as there are no restrictions upon transactions other than that associated with possible incom pleteness of the set of securities that are traded the result is sometimes called the fundamental theorem of asset pricing here we consider the extent to which such a result continues to be valid in the case of trading over an infinite horizon it has often been observed in the econometric literature on asset pricing bubbles that it is possible in principle for the price of a perpetuity and the dividends on that security to satisfy at all times a present value relation for one period holding returns while the security s price nonetheless does not equal the present value of the stream of dividends expected over the infinite future in such a case the price of the perpetuity is said to involve a bubble component 2 joint stochastic processes for which this component is nonzero are sometimes argued to characterize existing assets for a recent example see froot and obstfeld 1991 but such an inference depends upon aspects of the stochastic

incomplete preferences and equilibrium in contingent markets this paper shows that betting or speculative trading between agents with incomplete preferences is likely to occur if agents have access to convex choice sets this contrasts sharply with endowment economy models where preference incompleteness often hinders betting speculative trading or mutually beneficial insurance arrangements our results imply that decision makers with identical tastes and identical feasible sets will potentially gain from speculative trade for generic status quo allocations we also develop a framework for endogenizing the status quo allocations of decision makers that are treated exogenously in the existing literature finally we provide a tractable differential representation of status quo allocations equilibria and conditions where speculative trade may or may not emerge

utility over time the homothetic case the purpose of this paper is to show how the economics of choice over time can be strengthened by introduction of restrictive assumptions namely additivity and homotheticity of utility we consider applications to labor supply 2 savings behavior and long run distribution and welfare measurement labor supply is mainly a function of the ratio of non labor income to the wage rate savings generally increase with increases in the rate of interest in the long run distribution is not much dependent upon initial wealth and instead is mainly determined by attitudes towards time in the long run the as if social utility function is often well measured by consumer surplus the applications appear to be strong therefore it is appropriate to begin with a general argument for the main assumptions to be imposed two early contributions to the economics of time are by becker 1 and koopmans 111 the former presents a general framework without any specific assumptions about utility over time at most there is a homogeneous technology to produce consumption from goods and time pollak and wachter 131 koopmans 1 l adds highly intuitive assumptions to show utility additive and discounted over time koopmans analysis could be extended to cases where utility is additive merely between remote time periods see rader 15 pp 161 1851 this would correspond to the realistic case where the influence of distant consumption on preferences is negligible additivity must be reinterpreted in terms of a shifting environment of current consumption plus consumption sufficiently contiguous in time the analysis following could be adapted to this most compelling case merely adding utility over time does have implications for demand for example if complementaries occur between two goods they must occur between many others e g 15 pp 228 2331 however the results are meager and insufficient for the kind of analysis economists generally want to apply therefore we are led to add the assumption of homotheticity namely 219 0022 0531 81 050219 18 02 00 o

asset demands without the independence axiom an important application of the theory of choice under uncertainty is to asset markets and an important property in these markets is a preference for portfolio diversification if an investor is an expected utility maximizer then s he is risk averse if and only if s he exhibits a preference for diversification this paper examines the relationship between risk aversion and portfolio diversification when preferences over probability distributions of wealth do not have an expected utility representation

gravity in international finance abstract the past decade has witnessed an explosion of papers estimating gravity equations for cross border financial holdings without much of a theoretical foundation in this paper we develop a theory for bilateral asset holdings that takes a gravity form we discuss how to estimate international financial frictions and conduct comparative statics analysis within the context of the theory we also find though that reasonable extensions of the model no longer generate a gravity form while this does not significantly complicate estimation and comparative statics analysis it raises questions about the empirical validity of gravity specifications for cross border financial holdings that need to be addressed in future work

higher order risk attitudes a review of experimental evidence abstract this paper reviews the recent but fast growing experimental literature on higher order risk attitudes after introducing the theoretical context we first review the basic evidence and empirical moderators of these risk attitudes we then discuss recent extensions to ambiguity time risk and multi attribute utility in the last part we review indirect evidence from applied economic decision tasks

interim efficiency with meu preferences abstract recently kajii and ui 2009 17 proposed to characterize interim efficient allocations in an exchange economy under asymmetric information when uncertainty is represented by multiple posteriors when agents have bewley s incomplete preferences kajii and ui 2009 17 proposed a necessary and sufficient condition on the set of posteriors however when agents have gilboa schmeidler s maxmin expected utility preferences they only propose a sufficient condition the objective of this paper is to complete kajii and ui s work by proposing a necessary and sufficient condition for interim efficiency for various models of ambiguity aversion and in particular maxmin expected utility our proof is based on a direct application of some results proposed by rigotti shannon and stralecki 2008 24

survival with ambiguity we analyze a market populated by expected utility maximizers and smooth ambiguity averse consumers we study conditions under which ambiguity averse consumers survive and affect prices in the limit if ambiguity vanishes with time or if the economy exhibits no aggregate risk ambiguity averse consumers survive but have no long run impact on prices in both scenarios ambiguity averse consumers are fully insured against ambiguity in equilibrium and thus behave as expected utility maximizers with correct beliefs if ambiguity averse consumers are not fully insured against ambiguity their behavior mimics expected utility maximizers with wrong beliefs and a stochastic discount factor which might be consistently higher or lower than their actual discount factor we use this insight to analyze a markov economy with large persistent ambiguity consumers with decreasing absolute ambiguity aversion whose prudence with respect to ambiguity exceeds twice their absolute ambiguity aversion a s survive in the presence of expected utility maximizers with correct beliefs if the economy further exhibits aggregate risk they drive the expected utility maximizers out of the market and determine prices in the limit in contrast consumers with increasing or constant absolute ambiguity aversion only survive in the absence of aggregate risk and have no impact on limit prices

a more robust definition of subjective probability the goal of choice theoretic derivations of subjective probability is to separate a decisionmaker s underlying beliefs subjective probabilities of events from their preferences attitudes toward risk classical derivations have all relied upon some form of the marschak samuelson independence axiom or the savage sure thing principle which imply that preferences over lotteries conform to the expected utility hypothesis this paper presents a choice theoretic derivation of subjective probability in a savage type setting of purely subjective uncertainty which neither assumes nor implies that the decisionmaker s preferences over lotteries necessarily conform to the expected utility hypothesis copyright 1992 by the econometric society

consumer s surplus without apology the purpose of this paper is to settle the controversy surrounding consumer s surplus and by so doing to validate its use as a tool of welfare economics i will show that observed consumer s surplus can be rigorously utilized to estimate the unobservable compensating and equivalent variations the correct theoretical measures of the welfare impact of changes in prices and income on an individual i derive precise upper and lower bounds on the percentage errors of approximating the compensating and equivalent variations with consumer s surplus these bounds can be explicitly calculated from observable demand data and it is clear that in most applications the error of approximation will be very small in fact the error will often be overshadowed by the errors involved in estimating the demand curve the results in no way depend upon arguments about the constancy of the marginal utility of income consequently this paper supplies specific empirical criteria which can replace the apologetic caveats frequently employed by those who presently apply consumer s surplus moreover the results imply that consumer s surplus is usually a very good approximation to the appropriate welfare measures to preview below i establish the validity of these rules of thumb for a

uncertainty efficiency and incentive compatibility ambiguity solves the conflict between efficiency and incentive compatibility abstract a fundamental result of modern economics is the conflict between efficiency and incentive compatibility that is the fact that some pareto optimal efficient allocations are not incentive compatible this conflict has generated a huge literature which almost always assumes that individuals are expected utility maximizers what happens if they have other kind of preferences is there any preference where this conflict does not exist can we characterize those preferences we show that in an economy where individuals have complete transitive continuous and monotonic preferences every efficient allocation is incentive compatible if and only if individuals have maximin preferences

risk sharing in the small and in the large abstract this paper analyzes risk sharing in economies with no aggregate uncertainty when agents have non convex preferences in particular agents need not be globally risk averse or uncertainty averse in the sense of schmeidler 1989 we identify a behavioral condition under which betting is inefficient i e every pareto efficient allocation provides full insurance and conversely if and only if agents supporting probabilities defined as in rigotti et al 2008 have a non empty intersection our condition is consistent with empirical and experimental evidence documenting violations of convexity in either outcomes or utilities our results show that the connection between speculative betting and inconsistent beliefs does not depend upon global notions of risk or ambiguity aversion

the efficient use of conditioning information in portfolios we study the properties of unconditional minimum variance portfolios in the presence of conditioning information such portfolios attain the smallest variance for a given mean among all possible portfolios formed using the conditioning information we provide explicit solutions for n risky assets either with or without a riskless asset our solutions provide insights into portfolio management problems and issues in conditional asset pricing

subjective beliefs and ex ante trade we study a definition of subjective beliefs applicable to preferences that allow for the perception of ambiguity and provide a characterization of such beliefs in terms of market behavior using this definition we derive necessary and sufficient conditions for the efficiency of ex ante trade and show that these conditions follow from the fundamental welfare theorems when aggregate uncertainty is absent our results show that full insurance is efficient if and only if agents share some common subjective beliefs our results hold for a general class of convex preferences which contains many functional forms used in applications involving ambiguity and ambiguity aversion we show how our results can be articulated in the language of these functional forms confirming results existing in the literature generating new results and providing a useful tool for applications

consumption dynamics in general equilibrium a characterisation when markets are incomplete we introduce a methodology for analysing infinite horizon economies with two agents one good and incomplete markets we provide an example in which an agent s equilibrium consumption is zero eventually with probability one even if she has correct beliefs and is marginally more patient we then prove the following general result if markets are effectively incomplete forever then on any equilibrium path on which some agent s consumption is bounded away from zero eventually the other agent s consumption is zero eventually so either some agent vanishes in that she consumes zero eventually or the consumption of both agents is arbitrarily close to zero infinitely often later we show that a for most economies in which individual endowments are finite state time homogeneous markov processes the consumption of an agent who has a uniformly positive endowment cannot converge to zero and b the possibility that an agent vanishes is a robust outcome since for a wide class of economies with incomplete markets there are equilibria in which an agent s consumption is zero eventually with probability one even though she has correct beliefs as in the example in sharp contrast to the results in the case studied by sandroni 2000 29 and blume and easley 2006 8 where markets are complete our results show that when markets are incomplete not only can the more patient agent or the one with more accurate beliefs be eliminated but there are situations in which neither agent is eliminated c 2010 elsevier inc all

ambiguity aversion in the long run to disagree we must also agree abstract we consider an economy populated by smooth ambiguity averse agents with complete markets of securities contingent to economic scenarios where bankruptcy is permitted but there is a penalty for it we show that if agents posterior belief reductions given by their average probabilistic beliefs do not become homogeneous then an equilibrium does not exist it is worth noting that our main result does not imply any convergence of ambiguity perception or even the attitudes towards it in this way complete markets with default and punishment allow for ambiguity aversion in the long run and the agents can disagree on their ambiguity perception but they must agree on their expected beliefs

a definition of uncertainty aversion a definition of uncertainty or ambiguity aversion is proposed it is argued that the definition is well suited to modelling within the savage as opposed to anscombe and aumann domain of acts the defined property of uncertainty aversion has intuitive empirical content behaves well in specific models of preference multiple priors and choquet expected utility and is tractable tractability is established through use of a novel notion of differentiability for utility functions called eventwise differentiability

decision theory under ambiguity we review recent advances in the field of decision making under uncertainty or ambiguity we start with a presentation of the general approach to a decision problem under uncertainty as well as the standard bayesian treatment and issues with this treatment we present more general approaches choquet expected utility maximin expected utility smooth ambiguity and so forth that have been developed in the literature under the name of models of ambiguity sensitive preferences we draw a distinction between fully subjective models and models incorporating explicitly some information we review definitions and characterizations of ambiguity aversion in these models we mention the challenges posed by some of the models presented we end with a review of part of the experimental literature and applications of these models to economic settings

when does aggregation reduce risk aversion we study the problem of risk sharing within a household or syndicate a household shares risky prospects using a social welfare functional we characterize the social welfare functionals such that the household is collectively less risk averse than each member and satisfies the pareto principle and an invariance axiom we single out the sum of certainty equivalents as the unique member of this family which is quasiconcave over riskless allocations

the recursive core core allocations may be defined for infinite horizon capital accumulation models if agents cannot trust each other in the sense of gale then agents may renege on their commitments their decisions appear time inconsistent a core allocation is a recursive core allocation provided no coalition can improve upon its consumption stream at any time given its accumulation of assets up to that period we show for every allocation of consumption in the initial core one can find a distribution of capital stocks among the agents where no coalition of agents will break the initial core contract at any date it follows that if the proper distribution of the streams of capital is achieved then the allocation in the core is also in the recursive core the latter therefore forges a link between the distribution of wealth capital the problem of trust and time consistent intertemporal contracts

financial market structures revealed by pricing rules efficient complete markets are prevalent abstract it is well known that when an arbitrage free financial market is incomplete or has tradable financial assets with frictions there must be multiple risk neutral probability measures the main motivation for the present study is to elucidate what type of market structure usually emerges from pricing rules first we obtain that finitely generated pricing rules characterized by polytopes of probabilities capture the class of all finite arbitrage free financial markets that are potentially incomplete or subject to frictions affecting tradable assets next we provide a novel characterization of efficient securities and introduce related notions of market completeness that underlies pricing rules our main result shows that the class of efficient complete markets with bid ask spreads is the prevalent case revealed by finitely generated pricing rules

efficient allocations under ambiguity abstract important implications of the expected utility hypothesis and risk aversion are that if agents have the same probability belief then consumption plans in every efficient allocation of resources under uncertainty are comonotone with the aggregate endowment and if their beliefs are concordant then the consumption plans are measurable with respect to the aggregate endowment we study these two properties of efficient allocations for models of preferences that exhibit ambiguity aversion using the concept of conditional beliefs which we introduce in this paper we provide characterizations of such conditional beliefs for the standard models of preferences used in applications

political hierarchies and political shirking abstract we analyze how citizens can screen candidates for high political office in a political hierarchy in our model politicians differ in willingness to misuse discretionary powers of office those politicians willing to abuse the powers of office knaves can be induced in a hierarchy to reveal their type while in low office thus disqualifying themselves for advancement hierarchy s capacity for screening knaves out of high office depends on the conditions for reappointment to low office a seemingly perverse rule that reappoints shirking politicians can perform well to demonstrate an empirical application we analyze shirking in the house bank check bouncing scandal

precautionary saving in the small and in the large the theory of precautionary saving is shown to be isomorphic to the arrow pratt theory of risk aversion making possible the application of a large body of knowledge about risk aversion to precautionary saving and more generally to the theory of optimal choice under risk in particular a measure of the strength of the precautionary saving motive analogous to the arrow pratt measure of risk aversion is used to establish a number of new propositions about precautionary saving and to give a new interpretation of the dreze modigliani substitution effect copyright 1990 by the econometric society

information aggregation in a noisy rational expectations economy abstract this paper analyzes a general equilibrium model of a competitive security market in which traders possess independent pieces of information about the return of a risky asset each trader conditions his estimate of the return both on his own private source of information and price which in equilibrium serves as a noisy aggregator of the total information observed by all traders a closed form characterization of the rational expectations equilibrium is presented a counter example to the existence of fully revealing equilibrium is developed