a computational scheme for the optimal strategy in an incomplete market abstract we examine the optimal portfolio selection problem of a single agent who receives an unhedgeable endowment the agent wishes to optimize his her log utility derived from his her terminal wealth we do not solve this problem analytically but construct a recursive computational algorithm which approximates the optimal one we present an intelligent initial portfolio which requires numerically about 25 fewer corrective steps in the algorithm than a random initial portfolio and outperforms the portfolio which ignores the unhedgeable risk of the endowment

why barriers to entry are barriers to understanding this paper discusses and criticizes the usual definitions of barriers to entry the failure of the concept of barrier to entry to incorporate a time dimension means that it is a concept that is in need of additional embellishment in order to be useful in a practical problem or for antitrust or regulatory proceedings this abstract was borrowed from another version of this item

a reexamination of purchasing power parity a multicountry and multiperiod study abstract this paper re examines the purchasing power parity ppp theory in a multiple exchange rate world owing to a lack of precision in estimating the parameters many authors concluded that ppp did not hold very well in the 1970s using a time series cross sectional estimation procedure we are unable to reject the hypothesis that ppp holds in several currencies simultaneously in addition the parameters are precisely estimated this result follows from the estimation procedure which allows us to exploit the cross sectional variation in the data and the contemporaneous correlation in the deviations from ppp

the collapse of purchasing power parities during the 1970 s one of the striking facts concerning the relationship beiveen prices and exchange rates during the 1970 s has been the dismal performance of the predictions of the simple versions of the purchasing power parity doctrine ppp that doctrine in its absolute version states that the equilibrium exchange rate between domestic and foreign currencies equals the ratio of domestic to foreign price levels the relative version of the doctrine relates equilibrium changes in exchange rates to changes in the ratio of domestic to foreign prices during the 1970 s short run changes in exchange rates bore little relationship to short run differentials in national inflation rates and frequently divergences from purchasing power parities have been cumulative this paper reviews and analyzes the empirical record of exchange rates and prices during the 1970 s and the analysis is based on the experience of the dollar pound the dollar frecch franc and the dollar dm exchange rates section 2 presents the evidence on ppp during the 1970 s and contrasts it with the evidence from the 1920 s a period during which the doctrine held up reasonably well this analysis is relevant for assessing whether the flexible exchange rate system was successful in providing national economies with an added degree of insulation from foreign shocks and whether it provided policymakers with an added instrument for the conduct of macroeconomic policy the evidence regarding devia tions from purchasing power parities is also relevant for determining whether there is a case for managed float section 3 attempts to explain what went wrong with

does anticipated aggregate demand policy matter further econometric results a heated debate has arisen over what modigliani has dubbed the macro rational expections mre hypothesis this hypothesis embodies two component hypotheses 1 rational expectations and 2 short run neutrality i e that anticipated changes in aggregate demand will have already been taken into account in economic agents behavior and will thus evoke no output or employment response together these component hypotheses imply that deterministic feedback policy rules will have no effect on business cycle fluctuations the irrelevance of these types of policy rules is inconsistent with much previous macro theorizing as well as with the views of policymakers it is thus an extremely controversial proposition which requires a wide range of empirical research this paper is a sequel to a previous paper by the author that paper developed a methodology for testing the mre hypothesis and found that anticipated money growth does matter to the business cycle this paper extends the analyses to cases where the rate of nominal gnp growth or the inflation rate rather than money growth is the aggregate demand variable the empirical results are also negative on the mre hypothesis and its corresponding policy ineffectiveness proposition this abstract was borrowed from another version of this item

optimal portfolio choice for long horizon investors with nontradable labor income this paper examines how risky labor income and retirement affect optimal portfolio choice with idiosyncratic labor income risk the optimal allocation to stocks is unambiguously larger for employed investors than for retired investors consistent with the typical recommendations of investment advisors increasing idiosyncratic labor income risk raises investors willingness to save and reduces their stock portfolio allocation towards the level of retired investors positive correlation between labor income and stock returns has a further negative effect and can actually reduce stockholdings below the level of retired investors financial advisors typically recommend that their customers invest more in stocks than in safe assets when they are working and to shift their investments towards safe assets when they retire jagannathan and kocherlakota 1996 malkiel 1996 by contrast the standard academic models of portfolio choice merton 1969 1971 samuelson 1969 show that retirement is irrelevant for portfolio decisions if investment opportunities are constant and human capital is tradable in this case the fraction of wealth optimally invested in risky assets should be constant over the lifetime of an individual recent research building on the pioneering work by merton 1971 shows that time varying investment opportunities result in portfolio rules with an intertemporal hedging component whose magnitude depends on the investment horizon of the investor kim and omberg 1996 balduzzi and lynch 1997 brennan schwartz and lagnado 1997 brandt 1999 campbell and viceira 1999 2001 barberis 2000 with time variation in investment opportunities retirement and death play an instrumental role as events that exogenously fix the individual s investment horizon more importantly retirement also marks the time at which individuals stop working and thereafter must live off their lifetime savings and possibly transfers from this perspective retirement matters for portfolio choice

real and nominal shocks in a two country price setting world abstract this paper develops a two country model in which the law of one price does not hold in the short run and which is consistent with the stylized fact that exchange rates respond more quickly to news than prices this is done by assuming that firms face lumpy information costs in determining what price to charge both domestic and imported goods prices are therefore sticky with respect to news and deviations from the law of one price ppp are due to exchange rate surprises the model is used to analyze the domestic and international impact of real and nominal disturbances

life cycle portfolio choice with additive habit formation preferences and uninsurable labor income risk this article explores the implications of additive and endogenous habit formation preferences in the context of a life cycle model of an investor who has stochastic uninsurable labor income to solve the model i analytically derive the habit wealth feasibility constraints and show that they depend on the worst possible path of future labor income and on the habit strength but not on the probability of the worst income when there is only a slim chance of a severe income shock the model implies much more conservative portfolios the model also predicts that for some low to moderately wealthy households the portfolio share allocated to stocks increases with wealth because of this feature the model can generate more conservative portfolios for younger than for middle aged households the effects of habits on portfolio choice are robust to income smoothing through borrowing or flexible labor supply one controversial finding is that for high values of the habit strength parameter usually required for the resolution of asset pricing puzzles in general equilibrium the life cycle model predicts counterfactually high wealth accumulation jel g11 g12 copyright 2007 oxford university press

optimal consumption portfolio choices and retirement planning abstract we examine consumption and investment decisions in a life cycle model with habit formation stochastic opportunity set stochastic wages and labor supply flexibility retirement is taken into account by specifying an age at which labor earnings stop but consumption spending continues explicit solutions are obtained for optimal consumption labor supply and the financing portfolio we examine the structure and determinants of the optimal portfolio we also study the effects of the retirement date and of habits on optimal decisions finally we conduct a preliminary analysis to assess the effects of a liquidity constraint on optimal consumption leisure choices

empirical determinants of purchasing power parity deviations abstract this paper investigates the empirical determinants of purchasing power parity ppp deviations over the recent period of flexible exchange rates transitory ppp deviations arise in a world in which prices are sticky but where exchange rates respond instantaneously to news permanent ppp deviations occur when price indices differ across countries and the world is subject to real shocks regressions consistent with the hypothesis that current exchange rate changes create immediate ppp deviations which are slowly dissipated but not eliminated imply that both sticky prices and real shocks are responsible for the recent failure of ppp

lifetime consumption and investment retirement and constrained borrowing retirement flexibility and inability to borrow against future labor income can significantly affect optimal consumption and investment with voluntary retirement there exists an optimal wealth to wage ratio threshold for retirement and human capital correlates negatively with the stock market even when wages have zero or slightly positive market risk exposure consequently investors optimally invest more in the stock market than without retirement flexibility both consumption and portfolio choice jump at the endogenous retirement date the inability to borrow limits hedging and reduces the value of labor income the wealth to wage ratio threshold for retirement and the stock investment

the locational choice for free trade zones rural versus urban options abstract urban and rural areas are compared as appropriate locations for a free trade zone within a developing country suffering from urban unemployment if domestic capital is mobile between the two regions then the rural area is shown to be preferable to the urban area and sufficient conditions for this conclusion are presented this conclusion may be reversed however if capital is sector specific the condition for this reversal is also discussed

optimal consumption and portfolio policies when asset prices follow a diffusion process abstract we consider a consumption portfolio problem in continuous time under uncertainty a martingale technique is employed to characterize optimal consumption portfolio policies when there exist nonnegativity constraints on consumption and on final wealth we also provide a way to compute and verify optimal policies our verification theorem for optimal policies involves a linear partial differential equation unlike the nonlinear partial differential equation of dynamic programming the relationship between our approach and dynamic programming is discussed we demonstrate our technique by explicitly computing optimal policies in a series of examples in particular we solve the optimal consumption portfolio problem for hyperbolic absolute risk aversion utility functions when the asset prices follow a geometric brownian motion the optimal policies in this case are no longer linear when nonnegativity constraints on consumption and on final wealth are included by these examples one can see that our approach is much easier than the dynamic programming approach

saving and investing for early retirement a theoretical analysis we study optimal consumption and portfolio choice in a framework where investors adjust their labor supply through an irreversible choice of their retirement time we show that investing for early retirement tends to increase savings and reduce an agent s effective relative risk aversion thus increasing her stock market exposure contrary to common intuition an investor might find it optimal to increase the proportion of financial wealth held in stocks as she ages and accumulates assets even when her income and the investment opportunity set are constant the model predicts a decrease in risk aversion following strong market gains like those observed in the nineties

flexible exchange rates prices and the role of news lessons from the 1970s recent experience with flexible exchange rate systems has led to renewed interest in the operation of foreign exchange markets as reflected in many recent studies of the principal determinants of exchange rates the 1970s witnessed the dramatic alteration of the international monetary system from a regime of pegged exchange rates which prevailed for about a quarter of a century since the bretton woods conference into a regime of flexible though managed rates as a consequence of the emergence of the new legal and economic system traders national governments and international organisations were confronted with new economic problems choices and instruments during the 1970s ex change rates fluctuated widely and inflation rates accelerated the international monetary system had to accommodate extraordinarily large oil related shocks which affected trade flows in goods and assets huge oil payments had to be recycled uncertainties concerning future developments in international politics reached new heights and the prospects for the world economy got gloomier these developments placed unprecedented pressures on the markets for foreign exchange as well as on other asset markets they were associated with a large slide in the value of the us dollar and resulted in speeding up the creation of new institutions like the european monetary system which provided the formal framework for the management of exchange rates among members

unemployment risks and optimal retirement in an incomplete market we develop a new approach for solving the optimal retirement problem for an individual with an unhedgeable income risk the income risk stems from a forced unemployment event which occurs as an exponentially distributed random shock the optimal retirement problem is to determine an individual s optimal consumption and investment behaviors and optimal retirement time simultaneously we introduce a new convex duality approach for reformulating the original retirement problem and provide an iterative numerical method to solve it reasonably calibrated parameters say that our model can give an explanation for lower consumption and risky investment behaviors of individuals and for relatively higher stock holdings of the poor we also analyze the sensitivity of an individual s optimal behavior in changing her wealth level investment opportunity and the magnitude of preference for postretirement leisure finally we find that our model explains a countercyclical pattern of the number of unemployed job leavers

a model of uk real effective exchange rate behaviour an integrated model of the uk real effective exchange rate is examined which links purchasing power parity with trade flow and asset market mechanisms furthermore time series and econometric analysis using quarterly data from 1972 to 1987 are applied the results obtained are broadly consistent with this model and imply that the uk real effective exchange rate index is constant in the long run

hedging in incomplete markets with hara utility in the context of merton s original problem of optimal consumption and portfolio choice in continuous time this paper solves an extension in which the investor is endowed with a stochastic income that cannot be replicated by trading the available securities the problem is treated by demonstrating using analytic and in particular viscosity solutions techniques that the value function of the stochastic control problem is a smooth solution of the associated hamilton jacobi bellman hjb equation the optimal policy is shown to exist and given in a feedback form from the optimality conditions in the hjb equation at zero wealth a fixed fraction of income is consumed for large wealth the original merton policy is approached we also give a sufficient condition for wealth under the optimal policy to remain strictly positive

nontraded assets in incomplete markets pricing and portfolio choice this paper examines portfolio choice and asset pricing when some assets are nontraded for instance when a country cannot trade claims to its output on world capital markets when a government cann

purchasing power parity and real factors it is acknowledged that purchasing power parity ppp fails in empirical tests the position adopted is that real factors are an omitted variable from the ppp relationship and are the cause of divergences from ppp the real exchange rate as being determined by supply and demand shift factors as in stockman 1987 and neary 1988 is modelled we then empirically estimate a real exchange rate equation and use the fitted value as a generated regressor in tests of ppp it is demonstrated that when changes in the real exchange rate are incorporated into the ppp relationship ppp improves

labor supply flexibility and portfolio choice in a life cycle model abstract this paper examines the effect of the labor leisure choice on portfolio and consumption decisions over an individual s life cycle the model incorporates the fact that individuals may have considerable flexibility in varying their work effort including their choice of when to retire given this flexibility the individual simultaneously determines optimal levels of current consumption labor effort and an optimal financial investment strategy at each point in his life cycle we show that labor and investment choices are intimately related the ability to vary labor supply ex post induces the individual to assume greater risks in his investment portfolio ex ante

explicit solutions to an optimal portfolio choice problem with stochastic income abstract this paper solves in closed form the optimal portfolio choice problem for an investor with negative exponential utility over terminal wealth facing imperfectly hedgeable stochastic income the returns on income and the stock are imperfectly correlated so the market is incomplete we identify how an investor adjusts their merton rev econ statist 51 1969 247 portfolio of the stock and riskless asset via an intertemporal hedging demand in reaction to the stochastic income under general assumptions on the process governing the income the sign of the hedging demand is the opposite of the sign of the correlation between the income and stock the optimal portfolio in the stock is long stock if the risk premium is positive and correlation negative and short if these signs are reversed specializing in turn to normally distributed income and lognormally distributed income with or without mean reversion the effect of a number of parameters on the optimal portfolio in the stock can be studied when the risk premium on the stock and correlation have opposite signs the optimal portfolio decreases in magnitude with risk aversion unhedgeable variance of income and time and increases in magnitude with the magnitude of correlation under both the lognormal without mean reversion and normal models for income these relationships do not necessarily hold if the signs on the risk premium and correlation are the same in particular the optimal portfolio is not necessarily monotone in risk aversion violating well known static results in models without income when income follows a lognormal model with mean reversion more complicated behavior can occur for instance the optimal portfolio does not have to be monotonic in time regardless of the signs of correlation and the risk premium

competition cooperation and the neighboring farmer effect abstract in this paper we propose a model that explains how cooperation can emerge spontaneously between firms in a highly competitive market environment the basic idea is that the more competitive is the market the less costly it is for firms to help each other like good neighbors cooperation takes the form of sharing technical know how which speeds up the adoption of new technologies normally developed elsewhere that spur industrial development the model comports with the development history of japan s first example of successful industrial development its cotton spinning industry whose conditions match those of firms in small open economies today

institutional determinants of new firm entry in russia a cross regional analysis we investigate how the regional institutional environment in particular the political environment affects russian new firm entry across regions industries firm size classes and time we find that entry rates in russia are explained by natural entry rates and the institutional environment industries that are characterized by low entry barriers in developed market economies are found to have lower entry rates in regions subject to greater political fluidity as in the case of gubernatorial change we also find that higher levels of political fluidity and democracy increase relative entry rates for small sized firms but reduce them for medium sized or large ones

on the deviations from purchasing power parity the case of the ringgit effective exchange rate the paper investigates the extent to which the ringgit exchange rate converges on its purchasing power parity level in the long run using the cointegration and variance ratio tests the results indicate that shifts in the real exchange rate are dominated by permanent stochastic shocks which prevent it from reverting to its ppp base level further analysis indicates that low frequency movements in the relative price of tradable goods and the external terms of trade cannot explain the long run swing in the real exchange rate

optimal retirement with unemployment risks abstract this paper investigates the optimal retirement of an individual in the presence of involuntary unemployment risks and borrowing constraints in a complete market with frictions we use an intensity model and loading factors to illustrate the involuntary unemployment risks and frictions in unemployment insurance markets using reasonably calibrated parameters we observe that high involuntary unemployment intensity and loading factors could be important explanations for the empirical findings emphasized in recent studies we also find that an individual with high leisure demand after retirement reduces consumption during retirement and increases stockholdings as retirement time approaches

contestable markets an uprising in the theory of industry structure comment a situation traditionally identified as conducive to imperfect competition is when average costs decline and the cheapest scale of production is large relative to the size of the market however some of the more recent literature on industrial organization has emphasized a supposed distinction between fixed costs of production and sunk costs of production a point frequently made is that while the possibility of sunk costs can create genuine barriers to entry pure fixed costs per se do not inhibit competitive market performance this approach finds its logical extreme in the norm or abstraction of perfect contestability perfect contestability is essentially a theory of the polar case of frictionless entry and exit as william baumol stated a contestable market is one into which entry is absolutely free and exit is absolutely costless p 3 certainly this is the most reasonable interpretation of a situation where potential entrants feel free to disregard an incumbent s price response suppose every potential and actual producer has access to the same technology in a perfectly contestable market there are no set up or shut down losses the main result is that even with declining average costs of production the incumbent firm does not dare to post a price higher than average cost price above cost invites being undercut by a hit and run shadow entrant capable of producing at the same flow rate and at identical unit cost during just the briefest instant of time i argue that this line of reasoning is misleading perfect contestability gets around the problem of increasing returns only by in effect assuming it away a hit and run technology makes the firm behave as if it is competitive in a market precisely because the convexity preconditions for competition are de facto being met in that market this comment shows that strictly speaking there is no such thing as a pure fixed cost unless there are sunk costs located somewhere in the relevant production technology all costs are variable as a matter of formal theory you cannot have a range of decreasing average cost without sunk costs presumably there is also an approximation theorem which states that when sunk costs are close to being negligible then average production costs are practically nondecreasing perfect contestability holds approximately in a market only to the extent that production costs for the market are approximately nondecreasing my discussion will be restricted to the familiar case of a single well defined homogeneous fully divisible commodity while more general approaches are possible for the sake of simplicity the following definition is used the average cost function a c y t describes say the minimum cost per unit of output produced at a uniform flow rate y throughout the time interval 0 t especially in applications to industrial organization theory it is essential to remember that cost functions are not generally timeless and that writing ac as a function of y alone can be dangerously vague behind the free entry and exit of a hitand run technology in a perfectly contestable market is the abstraction of no sunk costs investments are fully reversible because nothing is lost in setting up or shutting down production

sunk costs and antitrust barriers to entry us antitrust policy takes as its objective consumer welfare not total economic welfare with that objective joe bain s definition of entry barriers is more useful than george stigler s or definitions based on economic welfare it follows that economies of scale that involve sunk costs may create antitrust barriers to entry a simple model shows that sunk costs without scale economies may discourage entry without creating an antitrust entry barrier this abstract was borrowed from another version of this item

consumption and portfolio policies with incomplete markets and short sale constraints the infinite dimensional case abstract we employ a martingale approach to study a dynamic consumption portfolio problem in continuous time with incomplete markets and short sale constraints we introduce a notion of minimax local martingale and transform the dynamic problem into a static problem of maximizing expected utility over the consumption bundles that satisfy a single budget constraint formed using that measure we establish the existence of and characterize the minimax local measure provide sufficient conditions for the dynamic consumption portfolio problem to have a solution and relate the optimal policies to the solution of quasi linear partial differential equation

limited participation and consumption saving puzzles a simple explanation and the role of insurance in this paper we show that the existence of a large negative wealth shock and insufficient insurance against such a shock could explain both the limited stock market participation puzzle and the low consumption high savings puzzle we then conduct an empirical analysis on the relation between household portfolio choices and access to private insurance and various types of government safety nets the empirical results demonstrate that a lack of insurance against large negative wealth shocks is positively correlated with lower participation rates and higher saving rates overall the evidence suggests an important role of insurance in household investment and savings decisions

the transhipment problem smuggling and welfare in paraguay abstract this paper studies the effects of contraband on resource allocation and welfare using parguayan data a major portion of exports from this economy involves the transhipment of goods from third countries through paraguay to brazil and argentina to avoid trade taxes both explicit and implicit via quantitative restrictions and multiple exchange rates using international and paraguayan databases for 1990 we calculate that contraband accounted for 58 of exports and 31 of imports finally we estimate that such trade increased welfare by 2 1 of gdp