asset pricing in multiperiod securities markets the intertemporal models developed in this paper have been stimulated by the capital asset pricing model capm of sharpe and lintner and the role of factor structure in ross arbitrage pricing theory apt suppose that some one dimensional stochastic process s provides a sufficient statistic for aggregate consumption then a heuristic dynamic programming argument shows that s market wealth and the wealth derivative of the value function for any agent are all locally perfectly correlated it follows from merton s work that there is a linear relationship between the local mean return on a security and the local covariance of that return with the return on the market portfolio the formal development uses martingale representation and martingale projection to obtain an intertemporal capm the history of a scalar brownian motion plays the role of a sufficient statistic we motivate the assumption of a sufficient statistic for aggregate consumption by considering a countable set of securities whose payoffs have an approximate factor structure where the factor components are in the information set generated by an n dimensional brownian motion and the idiosyncratic components are weakly correlated the approximate factor structure on the security payoffs implies that the rates of return have locally an approximate factor structure the role of the market portfolio can now be played by a set of n well diversified portfolios

option pricing when the variance changes randomly theory estimation and an application in this paper we examine the pricing of european call options on stocks that have vari ance rates that change randomly we study continuous time diffusion processes for the stock return and the standard deviation parameter and we find that one must use the stock and two options to form a riskless hedge the riskless hedge does not lead to a unique option pricing function because the random standard deviation is not a traded security one must appeal to an equilibrium asset pricing model to derive a unique option pricing function in general the option price depends on the risk premium associated with the random standard deviation we find that the problem can be simplified by assuming that volatility risk can be diversified away and that changes in volatility are uncorrelated with the stock return the resulting solution is an integral ofthe black scholes formula and the distribution function for the variance of the stock price we show that accurate option prices can be computed via monte carlo simulations and we apply the model to a set of actual prices

the pricing of options on assets with stochastic volatilities one option pricing problem that has hitherto been unsolved is the pricing of a european call on an asset that has a stochastic volatility this paper examines this problem the option price is determined in series form for the case in which the stochastic volatility is independent of the stock price numerical solutions are also produced for the case in which the volatility is correlated with the stock price it is found that the black scholes price frequently overprices options and that the degree of overpricing increases with the time to maturity one option pricing problem that has hitherto remained unsolved is the pricing of a european call on a stock that has a stochastic volatility from the work of merton 12 garman 6 and cox ingersoll and ross 3 the differential equation that the option must satisfy is known the solution of this differential equation is independent of risk preferences if a the volatility is a traded asset or b the volatility is uncorrelated with aggregate consumption if either of these conditions holds the risk neutral valuation arguments of cox and ross 4 can be used in a straightfoward way this paper produces a solution in series form for the situation in which the stock price is instantaneously uncorrelated with the volatility we do not assume that the volatility is a traded asset also a constant correlation between the instantaneous rate of change of the volatility and the rate of change of aggregate consumption can be accommodated the option price is lower than the blackscholes b s 1 price when the option is close to being at the money and higher when it is deep in or deep out of the money the exercise prices for which overpricing by b s takes place are within about ten percent of the security price this is the range of exercise prices over which most option trading takes place so we may in general expect the b s price to overprice options this effect is exaggerated as the time to maturity increases one of the most surprising implications of this is that if the b s equation is used to determine the implied volatility of a near the money option the longer the time to maturity the lower the implied volatility numerical solutions for the case in which the volatility is correlated with the stock price are also examined the stochastic volatility problem has been examined by merton 13 geske 7 johnson 10 johnson and shanno 11 eisenberg 5 wiggins 16 and

option valuation with systematic stochastic volatility we use an extension of the equilibrium framework of rubinstein 1976 and brennan 1979 to derive an option valuation formula when the stock return volatility is both stochastic and systematic our formula incorporates a stochastic volatility process as well as a stochastic interest rate process in the valuation of options if the mean volatility and covariance processes for the stock return and the consumption growth are predictable our option valuation formula can be written in preference free form further many popular option valuation formulae in the literature can be written as special cases of our general formula in this paper we investigate the valuation of individual stock options when the volatility of the underlying stock return is stochastic and has a systematic component which is related to the stochastic volatility of the consumption growth or the market return such an investigation is timely and of significant interest because there is now a considerable amount of evidence that the volatility of stock prices is not only stochastic but that it is also highly correlated with the volatility of the market as a whole for example see black 1975 conrad kaul and gultekin 1991 jarrow and rosenfeld 1984 jorion 1988 and ng engle and rothschild 1992 furthermore empirical work by black and scholes 1972 gultekin rogalski and tinic 1982 and whaley 1982 has shown that the empirical biases inherent in the black scholes option prices are different for options on high and low risk stocks because low risk stocks are mainly large firm stocks with stochastic return volatilities that are highly correlated with the return volatility of the market and high risk stocks are mainly small firm stocks with a lessimportant systematic volatility component incorporating systematic volatility effects in option valuation models has the potential to reduce the empirical biases exhibited by prices computed from the black scholes formula we use equilibrium arguments that extend the consumption based representative agent framework of rubinstein 1976 brennan 1979 and stapleton and subrahmanyam 1984 to allow individual asset returns and the consumption growth to exhibit stochastic volatility in particular we permit the volatility of individual asset returns to consist of a systematic component that is related to the consumption or market volatility in addi

the impact of the global food crisis on self assessed food security the paper provides the first large scale survey based evidence on the impact of the global food crisis of 2007 08 using an indicator of self assessed food security from the gallup world poll for the sampled countries as a whole this subjective indicator of food security remained the same or even improved seemingly owing to a combination of strong economic growth and limited food inflation in some of the most populous countries particularly india however these favorable global trends mask divergent trends at the national and regional levels with a number of countries reporting substantial deterioration in food security the impacts of the global crisis therefore appear to be highly context specific

jump risks and the intertemporal capital asset pricing model the specification of the stochastic process for stock prices is an important assumption underlying most equilibrium and option pricing models in modern finance this is particularly true of the continuous time capital asset pricing models where it is assumed that asset prices follow diffusion processes with continuous sample paths see merton 1973a breeden 1979 grossman and shiller 1982 the extent to which the implications of these models generalize to discontinuous sample paths is an unanswered question in theoretical finance however the answer to this question is of more than just theoretical interest since accumulated empirical evidence appears to be inconsistent with the continuous sample path assumption see rosenberg 1972 oldfield rogalski and jarrow 1977 rosenfeld 1982 one purpose of this paper is to provide some answers to this question we do this by extending merton s 1973a intertemporal asset pricing model in the special case of a constant investment opportunity set to include discontinuous sample paths for asset prices the constant investment opportunity set assumption is imposed because we are interested in obtaining sufficient conditions under which an instantaneous capital asset pricing model capm results the extension of our model to a stochastic opportunity set is discussed briefly in the text this paper investigates an economy where stock prices follow a jump diffusion process the first part of the analysis derives a sufficient condition under which an instantaneous capm will characterize equilibrium expected returns the sufficient condition is that the jump component of a stock s return must be unsystematic and diversifiable in the market portfolio the second part of the paper is an empirical investigation of the satisfaction of this condition the evidence is seen to be inconsistent with the satisfaction of this hypothesis that is the market portfolio appears to contain a jump component

on jumps in common stock prices and their impact on call option pricing the black scholes call option pricing model exhibits systematic empirical biases the merton call option pricing model which explicitly admits jumps in the underlying security return process may potentially eliminate these biases we provide statistical evidence consistent with the existence of lognormally distributed jumps in a majority of the daily returns of a sample of nyse listed common stocks however we find no operationally significant differences between the black scholes and merton model prices of the call options written on the sampled common stocks

pricing european currency options a comparison of the modified black scholes model and a random variance model we use the modified black scholes model and a random variance option pricing model to study prices of european currency options traded in geneva the options which cannot be exercised early include calls and puts on the dollar swiss franc exchange rate in the empirical analysis we examine the model fit and the biases with respect to the strike price time to maturity and volatility there is some evidence of mispricing and there are small gains available by trading with the random variance model

measuring food insecurity the frequency and severity of coping strategies abstract defining and interpreting food security and measuring it in reliable valid and cost effective ways have proven to be stubborn problems facing researchers and programs intended to monitor food security risks this paper briefly reviews the conceptual and methodological literature on food insecurity measurment describes a particular method for distinguishing and measuring short term food insecurity at the household level and discusses ways of generalizing the method the method developed enumerates the frequency and severity of strategies relied on by urban households when faced with a short term insufficiency of food this method goes beyond more commonly used measures of caloric consumption to incorporate vulnerability elements of food insecurity as well as the deliberate actions of household decision makers when faced with food insufficiency

stock price distributions with stochastic volatility an analytic approach we study the stock price distributions that arise when prices follow a diffusion process with a stochastically varying volatility parameter we use analytic techniques to derive an explicit closed form solution for the case where volatility is driven by an arithmetic ornstein ublenbeck or ar1 process we then apply our results to two related problems in the finance literature 1 options pricing in a world of stochastic volatility and 2 the relationship between stochastic volatility and the nature of fat tailes in stock price distributions article published by oxford university press on behalf of the society for financial studies in its journal the review of financial studies

an intertemporal general equilibrium model of asset prices this paper develops a continuous time general equilibrium model of a simple but complete economy and uses it to examine the behavior of asset prices in this model asset prices and their stochastic properties are determined endogenously one principal result is a partial differential equation which asset prices must satisfy the solution of this equation gives the equilibrium price of any asset in terms of the underlying real variables in the economy in this paper we develop a general equilibrium asset pricing model for use in applied research an important feature of the model is its integration of real and financial markets among other things the model endogenously determines the stochastic process followed by the equilibrium price of any financial asset and shows how this process depends on the underlying real variables the model is fully consistent with rational expectations and maximizing behavior on the part of all agents our framework is general enough to include many of the fundamental forces affecting asset markets yet it is tractable enough to be specialized easily to produce specific testable results furthermore the model can be extended in a number of straightforward ways consequently it is well suited to a wide variety of applications for example in a companion paper cox ingersoll and ross 7 we use the model to develop a theory of the term structure of interest rates many studies have been concerned with various aspects of asset pricing under uncertainty the most relevant to our work are the important papers on intertemporal asset pricing by merton 19 and lucas 16 working in a continuous time framework merton derives a relationship among the equilibrium expected rates of return on assets he shows that when investment opportunities are changing randomly over time this relationship will include effects which have no analogue in a static one period model lucas considers an economy with homogeneous individuals and a single consumption good which is produced by a number of processes the random output of these processes is exogenously determined and perishable assets are defined as claims to all or a part of the output of a process and the equilibrium determines the asset prices our theory draws on some elements of both of these papers like merton we formulate our model in continuous time and make full use of the analytical tractability that this affords the economic structure of our model is somewhat similar to that of lucas however we include both endogenous production and

a continuous time arbitrage pricing model with stochastic volatility and jumps we formulate and test a continuous time asset pricing model using u s equity market data we assume that stock returns are driven by common factors including random jump size poisson processes and brownian motions with stochastic volatility the model places overidentifying restrictions on the mean returns allowing one to identify risk neutral probability distributions useful in pricing derivative securities we test for the restrictions and decompose moments of the asset returns into the contributions made by different factors our econometric methods take full account of time aggregation

temporal aggregation and the continuous time capital asset pricing model we examine how the empirical implications of the capital asset pricing model capm are affected by the length of the period over which returns are measured we show that the continuous time capm becomes a multifactor model when the asset pricing relation is aggregated temporally we use hansen s generalized method of moments gmm approach to test the continuous time capm at an unconditional level using size portfolio returns the results indicate that the continuous time capm cannot be rejected in contrast the discrete time capm is easily rejected by the tests these results have a number of important implications for the interpretation of tests of the capm which have appeared in the literature few results in finance are as familiar or as widely used as the linear relation between expected returns and market betas implied by the capital asset pricing model capm however because both the discrete and continuous time versions of the capm lead to this linear relation 1 the literature often fails to distinguish between their respective empirical implications for example discrete and continuous time models are frequently used interchangeably to motivate empirical tests that use discretely observed return data 2 this paper examines how the empirical implications of the capm are affected by the length of the period over which returns are measured 3 we show that if this period differs from the implicit time frame of the model then the familiar linear capm relation need not hold for the observed returns for example the capm can imply a multifactor expression for expected returns when the asset pricing relation is properly aggregated this aspect has many important implications for applied work as well as the interpretation of empirical tests of the capm that have appeared in the literature we illustrate the importance of the temporal aggregation issue by deriving the

how do indicators of household food insecurity measure up an empirical comparison from ethiopia abstract renewed emphasis on programs and policies aimed at enhancing food security has intensified the search for accurate rapid and consistent indicators measures of food security are urgently required for purposes of early warning assessment of current and prospective status of at risk populations and monitoring and evaluation of specific programs and policies different measures are often used interchangeably without a good idea of which dimensions of food security are captured by which measures resulting in potentially significant misclassification of food insecure populations the objective of this paper is to compare how the most frequently used indicators of food security portray static and dynamic food security among the same sample of rural households in two districts of tigray state northern ethiopia seven food security indicators were assessed the coping strategies index csi the reduced coping strategies index rcsi the household food insecurity and access scale hfias the household hunger scale hhs food consumption score fcs the household dietary diversity scale hdds and a self assessed measure of food security safs these indicators provide very different estimates of the prevalence of food insecurity but are moderately well correlated and depict generally similar food security trends over time we suggest that the differences in prevalence estimates and in some cases the weaker than expected correlation can be explained in three ways first the indicators differ in the underlying aspect of food security they attempt to capture second each indicator is likely only sensitive within a certain severity range of food insecurity and these ranges do not always overlap third categorization of the prevalence of food insecurity is strongly dependent on the choice of cut off points for valid reasons food insecurity has no accepted gold standard metric against which individual indicators can be gauged though without one it is difficult to say which indicator performs best in correctly and reliably identifying food insecure households the implication is that using more than one indicator is advisable and policy makers should be aware of what elements of food insecurity each indicator portrays

the crash of ʼ87 was it expected the evidence from options markets transactions prices of s p 500 futures options over 1985 1987 are examined for evidence of expectations prior to october 1987 of an impending stock market crash first it is shown that out of the money puts became unusually expensive during the year preceding the crash second a model is derived for pricing american options on jump diffusion processes with systematic jump risk the jump diffusion parameters implicit in options prices indicate that a crash was expected and that implicit distributions were negatively skewed during october 1986 to august 1987 both approaches indicate no strong crash fears during the 2 months immediately preceding the crash attempts to explain what caused the stock market crashes around the world in october 1987 have suffered from the paucity of major economic developments occurring around that time that could have triggered the crashes shifting expectations regarding monetary policy foreign investors fears of a dollar decline increasing riskiness of assets none of these appeared major enough if present at all to explain the magnitude of the crashes and although portfolio insurance strategies could conceivably magnify the effects of a jump in fundamentals the initiating jump in fundamentals appears to be lacking

a theory of the nominal term structure of interest rates a model of the nominal term structure of interest rates is developed that has a positive and stationary process for the interest rate and delivers closed form expressions for the prices of discount bonds and european options on bonds unlike the one state variable version of the cox ingersoll and ross 1985 model this model even in its one state variable version allows the term premium to change sign as a function of the state and the term to maturity and also allows for shapes of the yield curve that are observed in the u s data but that are disallowed in the cox ingersoll and ross model article published by oxford university press on behalf of the society for financial studies in its journal the review of financial studies

option pricing when the variance is changing the monte carlo method is used to solve for the price of a call when the variance is changing stochastically

on jump processes in the foreign exchange and stock markets exchange rates exhibit systematic discontinuities even after allowingfor conditional heteroskedasticity in the diffusion process the results are much more significant in theforeign exchange market than in the stock market which suggests differences in the structure of these markets finally this jump component is shown to explain some of the empirically observed mispricings in the currency options market the objective of this article is to analyze and compare the empirical distribution of returns in the stock market and in the foreign exchange market there are a number of reasons why a better understanding of the stochastic processes driving prices in these markets would be useful many financial models rely heavily on the assumption of a particular stochastic process while relatively little attention is paid to the empirical fit of the postulated distribution as a result models like option pricing models are applied indiscriminately to various markets such as the stock market and the foreign exchange market when the underlying processes may be fundamentally different the foreign exchange market for instance is characterized by active exchange rate man

option values under stochastic volatility theory and empirical estimates abstract this paper numerically solves the call option valuation problem given a fairly general continuous stochastic process for return volatility statistical estimators for volatility process parameters are derived and parameter estimates are calculated for several individual stocks and indices the resulting estimated option values do not differ dramatically from black scholes values in most cases although there is some evidence that for longer maturity index options black scholes overvalues out of the money calls in relation to in the money calls

maximum likelihood estimation of latent affine processes this article develops a direct filtration based maximum likelihood methodology for estimating the parameters and realizations of latent affine processes filtration is conducted in the transform space of characteristic functions with a version of bayes rule used for recursively updating the joint characteristic function of latent variables and the data conditional upon past data an application to daily stock returns over 1953 96 reveals substantial divergences from emm based estimates in particular more substantial and time varying jump risk the implications for stock index options prices are discussed

general equilibrium pricing of options on the market portfolio with discontinuous returns when the price process for a long lived asset is of a mixed jump diffusion type pricing of options on that asset by arbitrage is not possible if trading is allowed only in the underlaying asset and a risk less bond using a general equilibrium framework we derive and analyze option prices when the underlying asset is the market portfolio with discontinuous returns the premium for the risk of jumps and the diffusion risks forms a significant part of the prices of the options in this economy an attempted replication of call and put options by the black scholes type of trading strategies may require substantial infusion of funds when jumps occur we study the cost and risk implications of such dynamic hedging plans article published by oxford university press on behalf of the society for financial studies in its journal the review of financial studies