inefficient credit booms this paper studies the welfare properties of competitive equilibria in an economy with financial frictions hit by aggregate shocks in particular it shows that competitive financial contracts can result in excessive borrowing ex ante and excessive volatility ex post even though from a first best perspective the equilibrium always displays under borrowing from a second best point of view excessive borrowing can arise the inefficiency is due to the combination of limited commitment in financial contracts and the fact that asset prices are determined in a spot market this generates a pecuniary externality that is not internalized in private contracts the model provides a framework to evaluate preventive policies which can be used during a credit boom to reduce the expected costs of a financial crisis copyright 2008 wiley blackwell

detecting potential overbilling in medicare reimbursement via hours worked we propose a novel and easy to implement approach to detect potential overbilling based on the hours worked implied by the service codes which physicians submit to medicare using the medicare part b fee for service ffs physician utilization and payment data in 2012 and 2013 released by the centers for medicare and medicaid services we construct estimates for physicians hours spent on medicare beneficiaries we find that about 2 300 physicians representing about 3 percent of those with 20 or more hours of medicare part b ffs services have billed medicare over 100 hours per week we consider these implausibly long hours

prices and investment with collateral and default abstract this paper uses the framework of an olg economy with three period lived agents in which a durable good serves as collateral for loans to study the effect of an unanticipated income shock when the economy is in a steady state equilibrium we focus on the consequence of default on loans when the value of the collateral falls below the value of the debt it secures we analyze the impulse response functions of the price and production of the durable good and show that there is an asymmetry between the response of the price and investment of the durable good to a positive and a negative income shock arising from default on the collateralized loans we show that this asymmetry can be seen in the data on housing prices and construction and is attributable to the default on mortgages in periods of decreasing prices which acts as a turbo mechanism magnifying the decline in investment

securitized markets international capital flows and global welfare we study the effect of collateralized lending and securitization on the global supply of securitized assets welfare and international net and gross capital flows in a two country general equilibrium model with idiosyncratic investment risk the financial sectors in the two countries home and foreign differ by the collateral requirement for investment loans with home requiring lower margins in autarky home endogenously supplies more assets and enables more risk sharing upon financial integration capital flows from foreign to home leading to lower interest rates and an increase in the global supply of assets foreign enjoys substantial welfare gains through better risk sharing and portfolio reallocation while the welfare experience for home is ambiguous gross capital flows arise when agents face aggregate shocks to the expected payoff to investment projects but can collapse when shocks concern the variance of returns

verifying competitive equilibria in dynamic economies in this paper i examine e equilibria of stationary dynamic economies with heterogeneous agents and possibly incomplete financial markets i give a simple example to show that even for arbitrarily small e 0 allocation and prices can be far away from exact equilibrium allocations and prices that is errors in market clearing or individuals optimality conditions do not provide enough information to assess the quality of an approximation i derive a sufficient condition for an e equilibrium to be close to an exact equilibrium if the economic fundamentals are semi algebraic one can verify computationally whether this condition holds the condition can be interpreted economically as a robustness requirement on the set of e equilibria which form a neighbourhood of the computed approximation i illustrate the main result and the computational method using an infinite horizon economy with overlapping generations and incomplete financial markets copyright 2011 oxford university press

on non existence of markov equilibria in competitive market economies abstract this paper presents some examples of regular dynamic economies with externalities and taxes that either lack existence of a markov equilibrium or such equilibrium is not continuous these examples pose further challenges for the analysis and computation of these economies journal of economic literature classification numbers c10 c62

informal insurance arrangements with limited commitment theory and evidence from village economies recent work on consumption allocations in village economies finds that idiosyncratic variation in consumption is systematically related to idiosyncratic variation in income thus rejecting the hypothesis of full risk pooling we attempt to explain these observations by adding limited commitment as an impediment to risk pooling we provide a general dynamic model and completely characterise efficient informal insurance arrangements constrained by limited commitment and test the model using data from three indian villages we find that the model can fully explain the dynamic response of consumption to income but that it fails to explain the distribution of consumption across households

price discrimination by u s and german exporters the insensitivity of the u s trade balance to the sharp depreciation of the dollar in the past three years has revived interest in the relationship between exchange rates and the trade balance a central issue in most analyses of the relation between the current account and the exchange rate concerns the price adjustment process the simple integrated competitive market model predicts that local currency prices should change in proportion to the nominal exchange rate for a country too small to influence world prices the relationship between local currency import prices and exchange rates has been referred to as the pass through relationship in the empirical literature in international economics if the proportional relationship between import prices and exchange rates holds pass through is said to be complete accounts of recent u s experience cite the failure of dollar prices of imported goods to rise in proportion to exchange rates i e incomplete pass through as an important factor in explaining the persistence of the trade deficit unfortunately observations on pass through alone provide limited insight into the behavior of markets since incomplete pass through is consistent with at least two fundamentally different paradigms one is the standard competitive model of trade in which the law of one price holds but exchange rate fluctuations are associated with large changes in import demand due to other factors for example if dollar appreciation is correlated with increases in world demand and industry marginal cost is increasing then pass through will be less than complete the other is an imperfectly competitive model in which exporters are capable of price discriminating across destination markets a phenomenon paul krugman 1987 has labeled pricing to market in this model incomplete pass through is typically associated with fluctuations in the markup of price over marginal cost on exports 2 these fluctuations in markups are believed to be countryspecific they do not reflect the behavior of prices to other export destinations both models are plausible explanations of recent u s experience unfortunately it is impossible to distinguish between these competing models using only information on import prices and exchange rates for a single country in order to distinguish between the competing models an empirical analysis of goods prices and exchange rates must be capable of measuring either marginal cost or the markup over marginal cost either of these tasks poses formidable empirical problems much of the empirical literature in industrial organization has been concerned with precisely these issues since markups are an important measure of the competitiveness of industries

u s inequality debt constraints or incomplete asset markets abstract to examine the role of debt constraints and incomplete asset markets lack of insurance markets in explaining u s inequality we run horse races between competing models for a widely used model we decompose inequality into its fundamental driving forces the underlying source of inequality in all models is uninsurable idiosyncratic risk both debt constraints and incomplete asset markets are needed to account for inequality but asset market incompleteness is the key friction it better accounts for the concentration and dispersion of wealth and is the most costly friction in terms of welfare tight debt constraints are important for explaining the lower tail of the wealth distribution

liquidity constrained markets versus debt constrained markets this paper compares two different models in a common environment the first model has liquidity constraints in that consumers save a single asset that they cannot sell short the second model has debt constraints in that consumers cannot borrow so much that they would want to default but is otherwise a standard complete markets model both models share the features that individuals are unable to completely insure against idiosyncratic shocks and that interest rates are lower than subjective discount rates in a stochastic environment the two models have quite different dynamic properties with the debt constrained model exhibiting simple stochastic steady states while the liquidity constrained model has greater persistence of shocks

dynamic competitive economies with complete markets and collateral constraints in this article we examine the competitive equilibria of a dynamic stochastic economy with complete markets and collateral constraints we show that provided the sets of asset pay offs and of collateral levels are sufficiently rich the equilibrium allocations with sequential trades and collateral constraints are equivalent to those obtained in arrow debreu markets subject to a series of limited pledgeability constraints we provide both necessary and sufficient conditions for equilibria to be pareto efficient and show that when collateral is scarce equilibria are not only pareto inefficient but also often constrained inefficient in the sense that imposing tighter borrowing restrictions can make everybody in the economy better off we derive sufficient conditions for the existence of markov equilibria and for the case of two agents for the existence of equilibria that have finite support these equilibria can be computed with arbitrary accuracy and the model is very tractable

the dynamics of financially constrained arbitrage we develop a model of financially constrained arbitrage and use it to study the dynamics of arbitrage capital liquidity and asset prices arbitrageurs exploit price discrepancies between assets traded in segmented markets and in doing so provide liquidity to investors a collateral constraint limits their positions as a function of capital we show that the dynamics of arbitrage activity are self correcting following a shock that depletes arbitrage capital profitability increases and this allows capital to be gradually replenished spreads increase more and recover faster for more volatile trades although arbitrageurs cut their positions in these trades the least when arbitrage capital is more mobile across markets liquidity in each market generally becomes less volatile but the reverse may hold for aggregate liquidity because of mobility induced contagion

imperfect competition and exchange rate pass through in the food processing sector imperfect competition has become an important dimension of international trade theory helpman and krugman product differentiation and economies of scale are explicitly incorporated in the new trade theory policy prescriptions following from these models hinge critically on underlying assumptions particularly the form of strategic firm behavior competitive cournot or bertrand unfortunately these models do not lend themselves easily to empirical testing also little empirical information exists on the strategic behavior of firms in international markets thus various models and tests on different aspects of imperfect competition in trade have been proposed and implemented one form of imperfect competition in international trade that has received attention re

the competitive structure of u s agricultural exports the competitive structure of u s agricultural exports is examined using a model of exporter behavior based on pricing decisions across destination markets market power is revealed in the adjustment patterns of export prices in response to exchange rate movements the results reject the hypothesis that the export pricing decisions by u s firms are consistent with price discrimination across destination markets for cotton corn and soybeans the strongest evidence against the competitive market structure is obtained for international trade in wheat where results indicate that the two largest importers soviet union and prc may exert market power to obtain lower prices

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

market power and the pricing of commodities imported from developing countries the case of us vanilla bean imports abstract a declining trend in the prices of vanilla beans reduce export earnings of developing country exporters at the same time currencies for these developing countries have depreciated the new trade theories suggest that market structure plays an important role in relating exchange rate devaluations to price declines this paper investigates the market structure and estimates the impact of exchange rate movements on prices for vanilla beans imported by the usa from five producers of vanilla beans in developing countries unlike other studies the estimation is based on a fixed effects econometric model derived from the importer s profit equation and the pricing to market ptm hypothesis data are a pooled cross section and time series covering the period 1967 1997 the results reveal some evidence that us importers of vanilla beans have the market power to apply price discrimination and to adjust import prices in reaction to exchange rate movement vis a vis exporters

exchange rate pass through when market share matters the authors investigate the pass through from exchange rates to import prices when firms future demands depend on their current market shares they show that profit maximizing foreign firms may either raise or lower their dollar export prices when the dollar appreciates temporarily i e the pass through may be perverse and that current import prices may be more sensitive to expected future exchange rates than to current exchange rates they present evidence that suggests the behavior of expected future exchange rates may provide a clue to the puzzling recent behavior of u s import prices copyright 1989 by american economic association

asset shortages liquidity and speculative bubbles abstract we study the effect of asset shortages on liquidity in economies with limited enforcement of debt contracts we establish that under a suitable assumption in terms of gains from trade liquidity does not dry up and trading volumes do not disappear as credit conditions worsen the equilibrium outcome becomes arbitrarily close to a purely speculative equilibrium and bubbles occur in the limit the result applies to incomplete markets and more generally to equilibria where collateral constraints interfere with the additivity of the payoff pricing functional

growth cycles and market crashes abstract market booms are often followed by dramatic falls to explain this requires an asymmetry in the underlying shocks a straightforward model of technological progress generates asymmetries that are also the source of growth cycles assuming a representative consumer we show that the stock market generally rises punctuated by occasional dramatic falls with high risk aversion bad news causes dramatic increases in prices bad news does not correspond to a contraction of existing production possibilities but to a slowdown in its expansion this economy provides a model of endogenous growth cycles in which recoveries and recessions are dictated by the adoption of innovations journal of economic literature classification numbers o40 g12 o41 o30

stationary equilibria in asset pricing models with incomplete markets and collateral we consider an infinite horizon exchange economy with incomplete markets and collateral constraints as in the two period model of geanakoplos and zame 2002 households can default on their liabilities at any time and financial securities are only traded if the promises associated with these securities are backed by collateral we examine an economy with a single perishable consumption good where the only collateral available consists of productive assets in this model competitive equilibria always exist and we show that under the assumption that all exogenous variables follow a markov chain there also exist stationary equilibria these equilibria can be characterized by a mapping from the exogenous shock and the current distribution of financial wealth to prices and portfolio choices we develop an algorithm to approximate this mapping numerically and discuss ways to implement the algorithm in practice a computational example demonstrates the performance of the algorithm and shows some quantitative features of equilibria in a model with collateral and default

debt constrained asset markets we develop a theory of general equilibrium with endogenous debt limits in the form of individual rationality constraints similar to those in the dynamic consistency literature if an agent defaults on a contract he can be excluded from future contingent claims markets trading and can have his assets seized he cannot be excluded from spot markets trading however and he has some private endowments that cannot be seized all information is publicly held and common knowledge and there is a complete set of contingent claims markets since there is complete information an agent cannot enter into a contract in which he would have an incentive to default in some state in general there is only partial insurance variations in consumption may be imperfectly correlated across agents interest rates may be lower than they would be without constraints and equilibria may be pareto ranked

exchange rates and prices the adjustment of relative prices to exchange rate movements is explained in an industrial organization approach given labor costs in the respective currencies exchange rate movements change costs for firms selling in the home market and thus disturb the industry equilibrium the extent of absolute and relative price adjustment is shown to depend on market integration product substitutability the relative number of domestic and foreign firms and the market structure the impact of exchange rates on prices is illustrated in a variety of approaches including the cournot a dixit and j stiglitz 1977 and s salop 1979 models some empirical evidence is offered in support of the theory copyright 1987 by american economic association