the opportunity cost of mean variance choice under estimation risk abstract mean variance portfolio choice is often criticized as sub optimal in the more general expected utility framework it is argued that the expected utility framework takes into consideration higher moments ignored by mean variance analysis a body of research suggests that mean variance choice though arguably sub optimal provides very close to expected utility maximizing portfolios and their expected utilities basing its evaluation on in sample analysis where mean variance choice is sub optimal by definition in order to clarify this existing research this study provides a framework that allows comparing in sample and out of sample performance of the mean variance portfolios against expected utility maximizing portfolios our in sample results confirm the results of earlier studies on the other hand our out of sample results show that the expected utility model performs worse the out of sample inferiority of the expected utility model is more pronounced for preferences and constraints under which in sample mean variance approximations are weakest we argue that in addition to its elegance and simplicity the mean variance model extracts more information from sample data because it uses the covariance matrix of returns the expected utility model may reach its optimal solution without using information from the covariance matrix

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

on measuring the impact of unemployment benefits on the duration of unemployment spell abstract many empirical estimates of the impact of policy changes in unemployment benefit upon the duration of unemployment spell ignore the equilibrium effect i e the demand for labor is assumed to remain unchanged we argue that this assumption is impermissible

reservation wages and the cost of unemployment this paper studies direct evidence on reservation wages reported in great britain in 1982 to assess 1 whether such asking prices are high and 2 whether variations in these reservation wages are related to differences in measures of the subjective and objective costs of unemployment a majority overall and for various subgroups reports reservation wages no higher than own past wages adjusted for earnings growth but there is nonetheless considerable dispersion in the ratio of reservation to past wages reservation wages are somewhat related to measures of the differential cost of unemployment most clearly for men although the independent role of benefits is often imprecisely measured however exactly which of these costs matter differs significantly according to whether the separation from last employment was voluntary or involuntary copyright 1989 by the london school of economics and political science

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

reemployment probabilities and returns to matching the assumption of constant returns in the matching function embodied in most bilateral search models is crucial to ensure the uniqueness of the unemployment rate along a steady state growth path this article explores the empirical viability of this assumption by estimating individual reemployment probabilities on a sample of unemployment entrants i apply hazard models to survey data on both completed and uncompleted unemployment durations the hypothesis of constant returns to matching is not rejected on the basis of the evidence that the job finding hazard depends only on local labor market tightness and is independent of its size

the economic effects of unemployment insurance in canada an empirical analysis of ui disentitlement this article provides an overview of the canadian unemployment insurance ui program including its evolution salient features relative size and knowledge about its labor market impacts understanding of these impacts is limited and we conclude that an event study approach is a promising way to further this knowledge we examine the effects of the 1976 ui disentitlement of the elderly on their labor force behavior and find evidence of significant adverse selection effects interactions with the public pension system suggest that poverty among the elderly could be best addressed through changes in programs other than ui

a new foundation for the mean variance analysis abstract in this paper i re examine how the mean variance analysis is consistent with its traditional theoretical foundations namely stochastic dominance and the expected utility theory then i propose a simplified version of the coarse utility theory as a new foundation i prove that by assuming risk aversion and the normality of asset variables the simplified model is well behaved indifference curves are convex and the opportunity set is concave therefore there exist global optimal portfolios in the market finally i prove that decision making in accordance with the simplified model is consistent with the mean variance analysis

comparing large sample maximum sharpe ratios and incremental variable testing abstract most existing results on the distribution of the maximum sharpe ratio depend on the assumption of multivariate normal return distributions we use recent results from the literature to provide an analytical representation of the distribution of the difference between two maximum sharpe ratios for much less restrictive distributional assumptions both with and without short sales knowing the distribution of the difference enables us to test ex ante whether or not the inclusion of additional variables leads to a significant improvement in the maximum sharpe ratio in addition we characterize the optimal long only solution and provide conditions for global optimality

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

the impact of the potential duration of unemployment benefits on the duration of unemployment abstract this paper examines the impact of the potential duration of unemployment insurance ui benefits on unemployment in the united states first we use a large sample of household heads to examine differences in the unemployment spell distributions of ui recipients and nonrecipients sharp increases in the escape rate from unemployment both through recalls and new job acceptances are apparent for ui recipients around the time of benefits exhaustion such increases are not apparent at similar points of spell duration for nonrecipients second our analysis of accurate administrative data from 12 states indicates that a one week increase in potential benefit duration increases the average duration of the unemployment spells of ui recipients by 0 16 to 0 20 weeks

do benefit cuts boost job finding swedish evidence from the 1990s in june 1995 the swedish parliament decided to cut the replacement rate in unemployment insurance from 80 percent to 75 percent a change that took effect on january 1 1996 this paper examines h

an equilibrium model of search unemployment this paper develops a simple general equilibrium model with sequential search in which a nondegenerate wage offer distribution is endogenously determined we use this model to analyze the comparati

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

unemployment duration unemployment benefits and labor market programs in sweden abstract standard search theory as well as some empirical evidence suggest that an unemployed individual s probability of entering employment increases as he approaches the time when unemployment benefits are due to expire this pattern may not carry over to a country like sweden where labor market programs are targeted at the long term unemployed at risk of benefit exhaustion the paper examines transitions out of unemployment using data on unemployed individuals in sweden a semi parametric competing risks model for transitions to employment labor market programs and non participation is estimated there is some evidence that the exit rate from unemployment to employment increases as benefit exhaustion is approached

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

how income transfer programs affect work savings and the income distribution a critical review for helpful comments on earlier drafts we thank without implicating moses abramovitz yves balcer john bishop alan blinder richard burkhauser michael darby irwin garfinkel alan gustman daniel hamermesh martin holmer george jakubson robert lampman paul menchik robert moffitt michael murray joseph quinn timothy smeeding eugene smolensky barbara wolfe and two anonymous referees

an econometric analysis of reservation wages this paper describes an analysis of survey data on unemployed people who reported their asking wage and the wage they expected to earn we show that if agents behavior is described by the standard optimal job search model one can use these data to deduce structural parameters rather than estimate them and we report our deductions from two surveys 1 of british unemployed people

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

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

eefects of reintegration activities on the dutch labour market regarding levels of education in the netherlands during the early nineteen nineties social security administration offices and labour exchange offices decided to co operate goal of this cooperation is to support the reintegration of unemployed people into the labour market and to shorten the individual spells of unemployment as a result of the cooperation information is available about levels of education of the unemployed this article primarely focuses on the effects of reintegration activities on the duration of unemployment for different levels of education results of the analysis are compared with the human capital theory also the question is discussed whether within the framework of the cooperation persons with a higher level of education have shorter spells of unemployment finally there is an analysis of the effects of activities undertaken by the unemployed themselves to find a job people with a university degree have significant longer spells of unemployment the reintegration activities of the social security administr

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

the effects of unemployment compensation in general equilibrium with search unemployment it is shown that when the effects of an increase in unemployment subsidies are studied in a general equilibrium framework unemployment increases far less than in a partial partial model in fact the result may very well be a decrease in unemployment if the general equilibrium forces are strong enough in the model used in this paper an increase in unemployment compensation unambiguously decreases the rate of unemployment copyright 1990 by the editors of the scandinavian journal of economics

on earnings related unemployment benefits and their relation to earnings an aspect of unemployment in britain that has been much discussed in recent years is the possible disincentive effects of unemployment benefits paradoxically the actual pattern of receipt of those benefits is hardly considered at all one reason for this is the popular belief that actual receipt follows a well defined hypothetical pattern this belief is encouraged by the government s representation of the benefit system for instance the department of health and social security dhss regularly publish hypothetical calculations of benefit receipt e g social security statistics i982 table 46 i4 and government answers to parliamentary questions are typically based on these figures economists frequently take these hypothetical calculations at face value when trying to model the effect of unemployment benefits on labour supply in a time series framework or in the case of micro analysis make similar calculations for each individual in the data set calculations are based on a limited set of stylised rules which are considered to capture the essence of the workings of the benefit system however estimates of the disincentive effects of benefits do not appear to be robust to the method of calculation atkinson et al i984 this emphasises the need for more precise modelling of the determinants of benefit receipt this paper is concerned with modelling the receipt of the benefit that has been at the heart of the incentives debate earnings related supplement ers was the element of national insurance unemployment benefit in the united kingdom that was linked to some measure of past earnings several commentators in the mid1 970s purported to show that its introduction in i 966 led to a marked rise in unemployment in the late i96os e g maki and spindler i975 and its abolition under the i980 social security no 2 act was certainly due in part to the belief that it discouraged work in investigating the receipt of this benefit the paper provides a case study of the difficulties in modelling the incomes of the unemployed and a cautionary tale to any investigator who does not have all the information necessary for precise calculation of budget constraints the typical assumption that has been made when simulating ers in micro data sets of unemployed individuals is that the relevant earnings that generate an ers payment may be successfully proxied by normal weekly earnings immediately prior to unemployment we may call this proxy the hypothetical model of ers receipt and the focus of the analysis is a test of this model using data on

macroeconomic adjustment and poverty in selected industrial countries the business cycle affects the incidence of poverty as shown by evidence from australia sweden the united kingdom and the united states many of the poor in these countries are outside the labor markets and transfers are a major source of income for many others but the unemployment and wage reductions that occur in recession increase the incidence of poverty major causes of poverty are unemployment in australia and the united kingdom and low wages in the united states similar cyclical effects are observed in sweden but a vast transfer program virtually eliminates poverty there are several policy options for combating poverty caused by recession a combination of unemployment insurance for a limited period followed by a job guarantee is the most effective policy toward unemployment whereas poverty caused by low earnings can be remedied by redistribution through the tax system

unemployment duration and competing risks evidence from sweden the determinants of unemployment duration are studied in the presence of multiple exits out of unemployment the results indicate that state aggregation may be a severe problem in empirical analysis of a labor market such as the one in sweden estimating a joint model for all transitions out of unemployment leads to biased estimates since different transitions are governed by different mechanisms the results also indicate positive duration dependence in both transitions to regular employment and transitions out of the labor force but no duration dependence in transitions to public labor market programs i introduction during the last decade we have witnessed a rapidly expanding literature on the determinants of unemployment duration the main motivation for this development is that a large share of the increasing unemployment rates in most western economies since the mid 1970s may be attributed to increased unemployment duration see e g the survey by lofgren and engstrom 1988 most empirical studies formulate an estimating equation for the determinants of the outflow from unemployment in terms of the hazard function which describes the conditional probability of leaving unemployment these studies are typically based on an explicit or implicit assumption that the only relevant transition out of unemployment is reemployment in this paper it is argued that such an assumption which amounts to assuming that all transitions from unemployment are governed by the same mechanism may lead to state aggregation bias we have no a priori reason to believe that e g increased education has the same effect on transitions from unemployment to employment as on transitions from

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

inflation tax rules and investment some econometric evidence this paper presents econometric evidence on the effect of tax incentives on business investment in the united states in the period from 1953 through1978 the analysis emphasizes that the interaction of inflation and existing tax rules has contributed substantially to the decline of business investment since the late 1960 s because the investment process is far too complex for any simple econometric model to be convincing i have estimated three quite different models of investment behavior the strength of the empirical evidence rests on the fact that all three specifications support the same conclusion more generally the analysis and evidence show that theoretical models of macroeconomic equilibrium should specify explicitly the role of distortionary taxes especially taxes on capital income the failure to include such tax rules can have dramatic and misleading effects on the qualitative as well as the quantitative properties of macroeconomic theories this paper was presented as the fisher shultz lecture at the fourth world congress of the econometric society 29 august 1980 in aix en province this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this abstract was borrowed from another version of this item

unemployment insurance and involuntary unemployment the case of adverse selection abstract this paper studies the private and public provision of unemployment insurance in a model where equilibrium unemployment results from the use of the wage as a worker selection device it is shown that private provision will not occur essentially because those workers most desired by a firm place least value on such coverage respecting the same informational constraints public provision necessarily gives rise to some distortions in participation decisions but nonetheless is welfare improving in the aggregate

search behaviour transitions to non participation and the duration of unemployment using longitudinal micro data on unemployed individuals for 1983 85 a structural job search model is estimated the model allows for transitions from unemployment to nonparticipation an extended version of the model deals with the influence of on the job search and prospective wage increases on search behavior of the unemployed the empirical results show that the probability of accepting a job offer is almost one for most unemployed individuals a large portion of unemployment spells ends in a transition out of the labor force the effects of changes in benefits on duration appear to be extremely small copyright 1990 by royal economic society

how does the benefit effect vary as unemployment spells lengthen summary this paper investigates how the effect of income while unemployed on the probability of an individual leaving unemployment varies with the length of time that the individual has been unemployed we examine this question in the context of a variety of alternative econometric models we extend the proportional hazards model with unrestricted baseline hazard to one in which there are unrestricted effects of a subset of the explanatory variables and also consider models that can be estimated as series of binary response models the proportional hazard restrictions are rejected for the sample of british unemployed men analysed and in the binary sequence framework logit and probit models based on symmetric distributions dominate in likelihood terms the extreme value form model implied by extension of the proportional hazards formulation logit models with a flexible form for the duration dependence which also incorporate unobserved heterogeneity in a flexible way are estimated the results for all formulations indicate a rapidly declining effect of unemployment income as a spell lengthens with no significant effect for the long term unemployed the preferred specifications which allow for omitted heterogeneity indicate no significant effect after about 5 months and this result is robust to the inclusion or exclusion of previous labour market experience variables and to the choice of mixing distribution

diverse beliefs survival and the market price of risk we study prices and allocations in a complete markets pure exchange economy in which there are two types of agents with different priors over infinite sequences of the aggregate endowment aggregate consumption growth evolves exogenously according to a two state markov process the economy has two types of agents one that learns about transition probabilities and another that knows them we examine allocations the market price of risk and the rate at which asset prices converge to values that would be computed under the assumption that all agents know the transition probabilities cogley and sargent 2008 showed that market prices of risk would be high in an economy with a risk neutral bayesian representative agent who learns about the parameters of a transition matrix for aggregate consumption growth starting with a pessimistic prior in 1933 1 this article studies the robustness of that finding to a per turbation that adds a small fraction of agents who know the parameters of the trans ition matrix traders participate in a walrasian equilibrium in which they do not infer information from prices grossman 1981 23 under what we assume to be the true data generating mechanism the survival of the fittest force analysed by blume and easley 2006 causes the more knowledgeable agents influence on equilibrium prices to grow over time along with their wealth we study how quickly that dissipates the effects of the initial pessimism of the less informed agents on equilibrium prices 4 to give the survival mechanism a large scope to moderate the effects of initial pessim ism we assume complete markets that allow agents to make trades of claims to wealth that are motivated solely by the different subjective probabilities they put on future states that gives the agents many opportunities to place bets that over time stochastically increase the share of wealth of the traders who know transition probabilities we solve a pareto problem to compute competitive equilibrium prices and alloca tions thereby implicitly defining an initial allocation of wealth we study how the market price of risk evolves as a function of the relative pareto weight on the better informed agent among other things we want to know how large the pareto weight on

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

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

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

searching for a will o the wisp an empirical study of the nairu in canada abstract this paper demonstrates the uncertainty surrounding estimates of the non accelerating inflation rate of unemployment nairu a reduced form phillips curve is used to develop a generic model of the nairu which nests competing hypotheses about the specific form of the inflation unemployment relationship empirical results for the canadian economy show that the range of prime age male nairu s generated by statistically satisfactory and economically reasonable estimating equations covers almost the entire range of canadian post war prime age male unemployment experience estimates of the nairu depend heavily on the form of the estimating equation the operational definition of key variables and the data sample period

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

reforming the labour market there is nothing new about government attempts to reform the labour market the primary emphasis put upon this aspect of economic policy by the two conservative gov ernments since 1979 however is perhaps unique this emphasis is in part the conse quence of a new stress on supply side economics and of a belief that many imperfections in the labour market are in fact removable by a mixture of measures de signed to alter the attitudes of both institutions and individuals and the environment in which they operate having been shocked into heightened receptiveness by the re cession actors and institutions have been regaled by a variety of measures these in clude trade union and industrial relations legislation the abolition of the fair wages resolution a review of wages councils measures on social security benefits initiatives on training and mobility incentives for individual and community enterprise and schemes to reduce the size of the effective labour force

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

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

reservation wage analysis of unemployed youths in australia this paper focuses on the analysis and structural estimation of the reservation wage function from a job search model using modified 2sls and maximum likelihood procedures with selectivity bias adj

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

risk aversion in the theory of expected utility with rank dependent probabilities expected utility with rank dependent probability theory is a model of decision making under risk where the preference relations on the set of probability distributions is represented by the mathematical expectation of a utility function with respect to a transformation of the probability distributions on the set of outcomes this paper defines based on g teaux differentiability measures of risk aversion for such preferences which characterize the relation more risk averse and applies these measures to the analysis of unconditional and conditional portfolio choice problems

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

search models and applied labor economics individual effects in a nonlinear model explicit treatment of heterogeneity in the empirical job search model this paper extends the empirical version of a job search model to permit heterogeneity in the location of wage offer distributions population variance in wage offers is decomposed into variance due to heterogeneity and variance facing each individual heterogeneity is found to be an important source of offer variance in the population the amount of pure wage offer dispersion facing individuals is found to contribute little to population variance

on the continuum approach of spatial and some local public goods or product differentiation models some problems abstract models with a continuum of consumers and locations such that each consumer can purchase goods in only one location are examined such models are common in the literature of the new urban economics an approximation by economies with a finite number of consumers is shown to fail in the first two examples the continuum economy equilibrium exists and is unique but the finite economy has many equilibria example 1 or none at all example 2 in example 3 the continuum economy has no equilibrium but the finite economy has one these three examples employ location dependent utilities the fourth example illustrates the conceptual difficulties that arise in approximation when transportation cost is introduced even with location independent utilities the results are related to the literatures concerning product differentiation and spatial economies

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

unemployment duration and individual heterogeneity a regional study this paper investigates the impact of individual heterogeneity and regional influences on unemployment duration utilizing cross section microeconomic data drawn from a representative random survey of individual job seekers for the english county of kent these individual level data are unique in that they provide information concerning the personal characteristics of job seekers alongside direct observations of both their reservation wages and job search behaviour such data are rare and to the authors knowledge have never before been utilized in a regional context thus the paper contributes to the empirical literature by analysing the extent to which individual heterogeneity and intra regional variation in labour market opportunities impact upon the observed distribution of unemployment duration s in particular the paper analyses the extent to which the duration of unemployment is determined by individual choice this is an important issue for the formation and evaluation of policy these result

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

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

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

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

ambiguity made precise a comparative foundation the theory of subjective expected utility has been recently extended to allow ambiguity to matter for choice we propose a notion of absolute ambiguity aversion by building on a notion of comparative ambiguity aversion we characterize it for a preference model which encompasses some of the most popular models in the literature we next build on these ideas to provide a definition of unambiguous act and event and show the characterization of the latter as an illustration we consider the classical ellsberg 3 color urn problem and find that the notions developed in the paper provide intuitive answers journal of economic literature classification number d81

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

household unemployment and the labour supply of married women a recent reform to the uk unemployment insurance ui system has reduced the duration of entitlement from 12 to six months the ui and welfare systems interact in the uk in such a way that exhaustion of ut for married individuals has potentially large disincentive effects on the labour supply of spouses a model of labour supply is estimated for married women allowing for endogenous unemployment durations of husbands and wives we distinguish between transfer programme induced incentive effects correlation between labour supply and wages within couples complementarity between the leisure times of spouses and a discouraged worker effect

endogenous unemployment insurance in a monopoly union model when job search matters abstract the aim of the paper is to derive an optimal unemployment insurance policy for a utilitarian trade union when job search matters it is shown that the well known result from the theory of insurance concerning the optimal risk sharing between risk averse agents changes essentially if the search behavior is allowed to affect the performance of the labor market we assume that labor market mismatch decreases with search effort which in turn decreases with the benefit the resulting equilibrium benefit is shown to be a decreasing function of the trade union s share of the costs of the insurance fund the model is also extended to the case where the benefit is made conditional on monitored search effort

unemployment benefit duration and incentives in britain how robust is the evidence abstract recent years have seen considerable advances in the econometric treatment of micro data in models of unemployment duration this paper examines the evidence from such models concerning the effects of unemployment benefits on incentives to work in britain widely accepted results of a small but significant benefit effect are reproduced using a sample of 1 231 unemployed men however these results are only found when benefit receipt is assumed to follow a hypothetical pattern which is shown to be unrealistic and over generous when more realistic calculations of benefits are used no benefit effect is found the paper also argues that search theory is of little help in determining the choice between competing functional forms and explanatory variables results concerning benefits are shown to be sensitive to the latter