more on estimation risk and simple rules for optimal portfolio selection for the risk averse investor consideration of estimation risk is important in selecting an expected utility maximizing portfolio it has previously been shown that the composition of the tangency portfolio is unaffected by the recognition of estimation risk if the full covariance model is used alternatively if the market model is used the composition of the tangency portfolio has been shown to be affected by the recognition of estimation risk however as is demonstrated in this paper the effect will generally not be as substantive as previously believed and in many situations can be safely ignored in order to determine the composition and location of an efficient frontier from which an optimal portfolio will be selected the investor must employ estimates of expected returns variances and covariances for the set of securities under consideration if the investor simply treats the estimated parameter values for the securities as true parameter values then estimation risk will have been ignored and as shown by barry 1 and klein and bawa 14 15 a suboptimal portfolio will most likely have been selected bawa brown and klein 6 and klein and bawa 14 discuss the effects of estimation risk on the selection of an optimal portfolio from a set of risky assets and note that the location but not the composition of the efficient frontier changes when estimation risk is recognized if security returns are generated by a stationary multivariate normal distribution for which the investor has a diffuse prior furthermore brown 8 has shown these results to be robust for severe misspecification of the underlying multivariate distribution of returns e g assuming it to be normal when in actuality it is student t with small degrees of freedom this paper is concerned with the effects of estimation risk on the composition of the tangency portfolio derived from a set of risky assets and a risk free asset under the assumption that the investor has a diffuse prior 1 barry 2 bawa and brown 4 and brown 7 have shown analytically that the composition of the tangency portfolio is unaffected by estimation risk if the full covariance model is used chen and brown 10 have expanded upon the work of brown 9 and have argued that if security returns are generated by the market model then the composition of the tangency portfolio will be substantively different when estimation risk is recognized

can learning affect exchange rate behavior the case of the dollar in the early 1980 s this paper demonstrates that a change in parameters of the money market that is not immediately understood will affect the behavior of exchange rate forecast errors while the market is learning the analysis is applied to the behavior of u s dollar german mark forecast errors during the early 1980 s when the market appeared to systematically underpredict the strength of the dollar consistent with this observation empirical estimates of implied forecast errors based upon bayesian learning suggest that forecast errors would have been on average negative during the period as the market came to realize the increase in u s money demand

productivity and distribution effects of codetermination in an efficient bargaining model codetermination can be regarded as an extreme regulatory intervention of the legislator in the labor market which might affect the efficiency of production and the bargaining power of labor based on a model that covers both efficient bargaining and employment bargaining a simple equation is derived that is suited to empirical testing the empirical test is based on german data and includes years before and after the extension of german codetermination law in 1976 the estimates determine the productivity of labor and relative bargaining power of capital and labor it turns out that codetermination does not affect productivity but leads to a significant increase in workers bargaining power and the distribution of rents

were price changes during the great depression anticipated abstract this paper reassesses whether the large swings in prices during the 1930 s were anticipated we argue that uncertainty about monetary fiscal and exchange rate policies induced systematic differences between the rate of price change expected by economic agents at the time and the time series forecasts of inflation our analysis of nominal interest rates and ex post inflation strongly supports this view in fact our results suggest that the deflation of the early depression years and the inflation that followed were both largely unanticipated

profitability and profit sharing claims that profit sharing is a purely distributive wealth confiscation scheme without incentive effects due to free rider problems are based on neglect of cooperation and interaction in the workforce when these activities are difficult to monitor directly group incentives such as profit sharing can increase efficiency and maintain a superior nashequilibrium with strictly individual optimization with simultaneous wls tobit estimates we find here strong effects of profit sharing and worker ownership shares on residual owners return on capital in medium sized metal working firms in west germany complementing earlier results on productivity

are product and process innovations independent of each other this paper studies the relationship between product and process innovation after discussing the determinants of product and process innovation a simultaneous equation model is estimated a positive impact of product innovation on process innovation can be proved but no evidence for a reverse effect to the respect to the inclusion of product innovation

cooperation productivity and profit sharing firm specific assets generate an ex post bargaining problem over surplus division and rational workers may collude to obtain a surplus share in nonpecuniary form through restriction of effort conversely profit sharing should motivate cooperation to increase productivity when work organization facilitates interaction and horizontal monitoring since productive effort yields positive externalities to workers under contractual surplus sharing in simultaneous tobit estimates we find a strong influence of profit sharing on factor productivity in a sample of medium sized metalworking capitalist firms in west germany proxies for human capital and organizational factors were included

the role of expectations in stabilization policy abstract this paper develops and tests a theory of the process by which private agents in an economy form expectations about government policy agents form and update their beliefs about the true state of government policy in a bayesian fashion the credibility of a policy is defined to be the subjective probability that the government is pursuing a reform policy rule the credibility of a reform of monetary or exchange rate policies is a function of the parameters of both monetary and fiscal policies the theory is applied to the chilean and argentine exchange reforms of the late 1970 s

the persistence of the peso problem when policy is noisy abstract the peso problem the market s belief that a discrete event may occur has frequently been blamed for the persistence of on average mistaken forecasts of macroeconomic variables this paper demonstrates how beliefs that a policy process may have switched can induce apparent ex post biased forecasts of exchange rates even after the switch has occurred furthermore during this peso problem period exchange rates may appear to contain a speculative bubble component since they will systematically deviate from the levels implied by observing fundamentals ex post and the conditional variance of exchange rates will exceed the variance implied by observing fundamentals

optimal portfolio selection under institutional procedures for short selling abstract this study presents and formally justifies a simple ranking approach for optimal portfolio selection under institutional procedures for short selling it also provides economic insights of the explicit solution of the portfolio problem the analysis is applicable to different treatments of the short sale proceeds and any margin deposits in contrast to previous approaches it does not require assumptions that overstate short sale benefits for maintaining analytical tractability and it can easily identify and filter out securities that are undesirable for investing or for short selling thus this study can enhance the usefulness of portfolio modeling for assisting practical investment decisions

using survey data to test standard propositions regarding exchange rate expectations survey data provide a measure of exchange rate expectations superior to the forward rate in that no risk premium interferes we estimate extrapolative adaptive and regressive models of expectations static or random walk expectations and bandwagon expectations are rejected current appreciation generates the expectation of future depreciation because variables other than the contemporaneous spot rate receive weight in comparing expectations to the process governing the spot rate we find statistically significant bias no variable is as ubiquitous in international financial theory and yet as elusive empirically as investors expectations regarding exchange rates in the past expectations have been modeled in an ad hoc way often by using the forward exchange rate there is however a serious problem with using the forward discount as the measure of the expected change in the exchange rate in that the two may not be equal the gap that may separate the forward discount and expected depreciation is generally interpreted as a risk premium most of the large empirical literature testing the unbiasedness of the forward exchange rate for example has found it necessary either arbitrarily to assume away the existence of the risk premium if the aim

economic effects of codetermination the success of west german scandinavian and japanese economies particularly when compared with lagging productivity and competitiveness of the u s and the u k have focused attention on comparative institutions in labour markets and corporate control declining unions and increasing reliance on competitive market pressures in the angloamerican countries contrast with more state intervention and regulation of the european social market economies as noted by henzler 1992

an alternative approach to the american demand for money with a decade of evidence behind it the profession seems to have agreed on the fact that a structural break shifted the american demand for money shortly after 1973 it is difficult to pinpoint the source of the trouble precisely let alone to explain the event with an econometric model in their survey judd and scadding 1982 tentatively concluded that financial innovation is the source of the problem while this conclusion has not been universally accepted the instability of the money demand function is largely taken as a given stylized fact the primary goal of this article is to provide an alternative solution to the case of the missing money using the methods of hendry 1979 it should be stressed at the outset that as this paper deals with a problem in the applied literature it is unabashedly empirical in nature the paper attempts to explain an empirical difficulty without presenting a new theoretical model of money demand rather in the context of the standard transactions demand theory for narrow money a number of questions are analyzed with an atypical econometric model was there actually a shift or a series of shifts in the demand for money if not why have other investigators concluded that there was in fact a shift most importantly what function seems to be the most reasonable approximation to the data generation process during the period in question

a critique of variance bounds tests for monetary exchange rate models note the monetary approach to exchange rate determination attributes the observed volatility of floating rates to revisions of expectations about current and future disturbances that affect the supply and demand conditions in the money market see for example frenkel and mussa 1980 a number of recent studies have proposed and implemented variance bounds tests of monetary exchange rate models along the lines of bond price and stock price volatility tests pioneered by leroy and porter 1981 shiller 1979 1981 and singleton 1980 huang 1981 presents evidence apparently demonstrating that some exchange rates are more volatile than a simple monetary model based on the assumptions of purchasing power parity and uncovered interest parity can rationalize meese and singleton 1983 derive but do not test the variance bounds implied by a number of monetary models vander kraats and booth 1983 henceforth referred to as v b implement volatility tests for three monetary models they conclude that only a variant of the sticky price model developed by dornbusch 1976 can potentially explain under certain rather implausible assumptions about parameter values the observed volatility of the exchange rates included in their sample in the literature this evidence of excess volatility of floating rates is considered damaging to the monetary approach and or to the rational expectations hypothesis for example in his recent survey of the literature richard levich remarks that on the basis of huang s results it follows that either the market is inefficient or that the rational expectations monetary model is incorrect or both levich 1985 p 994 the primary purpose of the present paper is to point out that the excess volatility evidence presented by huang and by ai b arises from a calculation error namely the value they assign to the interest semielasticity of money demand may be appropriate for a study using annual time series but is inappropriate for their monthly data once this error is corrected their exchange rate series no longer violate the variance bounds they test

testing for bubbles in exchange markets a case of sparkling rates this paper investigates the possibility that the observed deviations of major bilateral exchange rates from values implied by market fundamentals are a consequence of rational asset market bubbles when a new econometric methodology for detecting asset market bubbles is used the joint hypothesis of no bubbles and stable autoregressive processes for relative money supplies and real incomes is rejected for the dollar deutsche mark and dollar pound ratesusing monthly data over the period 1973 82 additional tests for coefficient stability and for lack of cointegration between exchange rates and market fundamentals suggest that the bubble findings must be interpreted with care

firm size and job quality a survey of the evidence from germany small firms provide and create a large proportion of jobs in germany are these jobs worse than jobs in larger firms the mosaic picture that emerges from a review of several recent empirical studies using german individual or firm level micro data shows that all in all wages are lower non wage incomes fringes are lower job security is lower work organisation is less rigid institutionalized possibilities for workers participation in decision making are weaker and opportunities for skill enhancement are worse in small firms compared to large firms the weight of evidence therefore indicates that on average small firms offer worse jobs than large firms it is argued that there is no need for policy measures targeted to improve job quality in small firms because higher incomes in large firms can in part be seen as compensating differentials for more rigid work organisation and can follow from wage policies to reduce shirking and turnover that is more costly in large than in small firms furthermore a lower level of remuneration less protection against dismissals a lower level of workers participation and less opportunities for further training all contribute to lower costs in small firms that might be needed to compensate for size related cost disadvantages compared to large firms economic policy should concentrate on keeping barriers to entrepreneurs entry to markets low to foster new firm formation and creative destruction

hours layoffs and unemployment insurance funding theory and practice in an international perspective the strikingly different behaviour of important economic aggregates in the united states and other industrial countries has received surprisingly little attention from economists among recent exceptions however gordon i 982 has shown that wages and hours of work are much more flexible in the united kingdom and japan than in the united states such relative hours variability is confirmed in a macro analysis by capdevielle and alvarez i98i and at micro level by sengenberger and kohler i982 the latter authors are concerned with labour market adjustment within the u s and west german automobile industries between i 97 i and i 980 estimates of the german workeroutput elasticity are found to be less than half that of the united states while the german hours elasticity is twice the united states figure at the national aggregate level capdevielle and alvarez also reveal much greater employment variability in the united states than in most other oecd countries in the years following the i973 74 opec supply shock much in line with these employment hours observations moy and sorrentino i98i argue that after

short selling and efficient sets the effect of short selling on the composition and location of the efficient set has been analyzed in a variety of ways however the situation typically facing investors where the initial margin requirement is less than 100 percent and the riskfree interest rate that is paid on the short proceeds is less than the rate paid on initial margin has not previously been considered the elton gruber padberg algorithm 1976 1978 subject to certain modifications is shown here to be capable of identifying the efflcient set under such conditions when harry markowitz 1952 developed the notion of efficient sets as a method of identifying an investor s optimal portfolio he did so in a setting where short selling was prohibited since then the effect of short selling on the composition and location of the efficient set has been considered in a variety of ways for example lintner 1965 suggested that short sales be treated from the perspective of a broker dealer where an amount of money equal to the short proceeds must be put up as initial margin with the short seller receiving riskfree interest on both the short proceeds and the margin alternatively black 1972 and merton 1972 assumed that the short seller did not have to put up any initial margin and that the short seller actually got the use of the short proceeds more recently dyl 1975 has assumed that the short seller must put up initial margin that is less than the short proceeds but receives no interest on either the margin or short proceeds this paper is concerned with the generation of efficient sets where short selling is allowed but with certain restrictions attached to it referred to hereafter as restricted short selling in particular initial margin is required but can be met by depositing interest bearing securities with the brokerage firm where the short seller s account is kept furthermore the model allows the short seller to earn interest on the short proceeds accordingly the model

parameter based decision making under estimation risk an application to futures trading this study shows how the standard portfolio model of futures trading should be modified when there is less than perfect information about the relevant parameters estimation risk the standard and the optimal decision rules for futures trading in the presence of estimation risk are compared and discussed an operational model of futures trading for use under estimation risk is advanced in the presence of relevant prior and sample information the model can be used to optimally blend both types of information many of the contributions of economic theory to the study of financial markets involve the use of parameters that are assumed known or estimable by the economic agents examples include the risk premium coefficient 18 and the security market lines that underlie the capital asset pricing model the volatility measures required for option pricing and the minimum variance hedge ratio and expected basis used to construct portfolios of futures contracts and cash positions generally it is left to practitioners to provide estimates of these parameters which are then directly substituted for the actual parameter values of the theoretical model whenever textbooks demonstrate how these parameters can be estimated there is usually a cookbook formula provided that requires some relatively straightforward analysis of the relevant data e g marshall 1989 chapters 6 and 7 cox and rubinstein 1985 chapter 6 the problems with the procedure described above are twofold first the theory has been slow to acknowledge that the practical application of the model almost always involves parameter estimates generally the additional risk of not knowing the true parameters is completely neglected second practitioners or the market participants will often have some type of nonsample information such as insider information or subjective priors that seems relevant for decision making however this potentially important information is ignored altogether when only sample data are used to obtain the parameter estimates

changing beliefs and systematic rational forecast errors with evidence from foreign exchange this paper addresses a new interpretation to the appearance in the early 1980s of systematic errors in forecasting the dollar exchange rate following a change in the process of a fundamental variable market participants revise their beliefs about the process using bayes rule since the market does not immediately recognize the change forecast errors are on average wrong during a period when the market is rationally learning for conservative parameter values the learning behavior of the dollar exchange rate in the early 1980s appears consistent with about half of the dollar s underprediction implied by the forward market copyright 1989 by american economic association

internal rent seeking works councils and optimal establishment size abstract using a microeconomic model and data from the establishment panel of the german institute for employment research we analyze the optimal establishment size against the background of rent seeking workers and the influence of works councils the theoretical part shows that establishment size has not only a discouragement effect on the level of individual rent seeking but also a quantity effect as the number of rent seekers increases the interplay of both effects together with technological considerations determines whether the employer chooses an inefficiently small or large establishment size introduction of a works council restores efficient establishment size although it is purely used as rent seeking device whether the employer benefits from a works council or not depends on the degree of contract incompleteness and the degree of worker coordination via a works council the empirical part indicates dominance of the discouragement effect over the quantity effect in establishments without works council as theoretically predicted works councils are beneficial by disentangling rent seeking and production issues thus eliminating the influence of the two rent seeking effects

estimation risk and simple rules for optimal portfolio selection elton gruber and padberg egp 6 7 have recently simplified the process of constructing optimal portfolios by developing simple criteria for optimal portfolio selection which do not involve use of mathematical programming their simple decision rules permit one to determine easily which securities to include in an optimal portfolio and how much to invest in each however in practical applications of theoretical models sample estimators are usually treated as if they were true values of unknown parameters as a result the effect of the standard errors of sample estimators on decision rules are completely ignored bawa brown and klein 1 have shown that what is optimal in the absence of estimation risk is not necessarily optimal or even approximately optimal in the presence of estimation risk moreover brown 4 examined optimal portfolio choice under uncertainty for various portfolio selection procedures the diffuse bayes rule the markowitz certainty equivalent ce rule the aggregation ce rule and the equal weight rule 1 and found that the diffuse bayes rule uniformly dominates the markowitz ce rule in repeated samples for the quadratic utility case as the sample size increases the bayes rule becomes superior to the aggregation ce and the equal weight rules in addition the result holds even where the probability distribution of returns is seriously misspecified thus brown s 4 study has clearly indicated that without taking estimation risk into account portfolio selection rules other than the bayes rule can lead investors to select suboptimal portfolios this paper shows by using the single index model for the return generating process that the simple decision rules for optimal portfolio selection derived by elton gruber and padberg 7 are not identical under the bayesian and the traditional methods of analysis 2 moreover in the case where short sales are not

accounting for exchange rate variability in present value models when the discount factor is near 1 a well known stylized fact about nominal exchange rates among low inflation advanced countries particularly u s exchange rates is that their logs are approximately random walks michael i mussa 1979 is most frequently cited for observing this regularity in a famous pair of papers richard a meese and kenneth rogoff 1983a b found that the structural models of the 1970 s could not beat a random walk in explaining exchange rate movements recently some authors menzie chinn and meese 1995 nelson mark 1995 mark and donggyu sul 2001 have argued that the models can outforecast the random walk at long horizons but a comprehensive recent study by yin wong cheung et al 2003 documents that no model consistently outperforms a random walk why one obvious explanation is that the macroeconomic variables that determine the exchange rate themselves follow random walks if the log of the nominal exchange rate is a linear function of forcing variables that are random walks then it will inherit the random walk property the problem with this explanation is that the economic fundamentals proposed in the most popular models of exchange rates do not in fact follow simple random walks one resolution to this problem is that there may be some other fundamentals ones that have been proposed in some models but are not easily measurable or ones that have not yet been proposed at all that are important in determining exchange rates if these unobserved fundamentals follow random walks and dominate the variation in exchange rate changes then exchange rates will nearly be random walks even if the standard observed fundamentals are not in engel and west 2003a hereinafter ew we propose an alternative explanation we consider linear models of the exchange rate that are in the asset market approach to exchange rates these models emphasize the role of expectations of future economic fundamentals in determining the current exchange rate the exchange rate expressed as the home currency price of foreign currency in this paper can be written as a discounted sum of the current and expected future fundamentals

accounting for forward rates in markets for foreign currency absteract forward and spot exchange rates between major currencies imply large standard deviations of both predictable returns from currency speculation and of the equilibrium price measure the intertemporal marginal rate of substitution representative agent theory with time additive preferences cannot account for either of these properties we show that the theory does considerably better along these dimensions when the representative agent s preferences exhibit habit persistence but that the theory fails to reproduce some of the other properties of the data in particular the strong autocorrelation of forward premiums since the advent of flexible exchange rates in the early 1970s a large body of statistical work has established that forward rates for major currencies are not optimal predictors of future spot rates relevant evidence is reported in studies by baillie lippens and mcmahon 1983 bekaert 1991 bilson 1981 boothe and longworth 1984 cumby 1988 cumby and obstfeld 1984 fama 1984 gregory and mccurdy 1984 hansen and hodrick 1983 hodrick and srivastava 1984 and korajczyk and viallet 1990 a more complete list of references is provided by hodrick 1987 these papers indicate that returns from speculation in forward and spot currency markets are predictable and that the predictable components vary considerably over time a number of alternative explanations have been offered for the predictable variation in foreign currency market excess returns kaminsky 1988 korajczyk 1985 and krasker 1980 suggest that infrequent extreme events may make returns appear predictable in small samples the so called peso problem lewis 1989 argues that rational learning following infrequent changes in the process governing equilibrium prices can explain part of the ex post predictability of currency returns froot and frankel 1989 and froot and thaler 1990 examine the hypothesis that market forecasts of future spot

capital labor and the firm a study of german codetermination under the german corporate governance system of codetermination employees are legally allocated control rights over corporate assets through seats on the supervisory board that is the board of nonexecutive directors the supervisory board oversees the management board the board of executive directors approves or rejects its decisions and appoints its members and sets their salaries we empirically investigate the implications of this sort of labor participation in corporate decision making we find that companies with equal representation of employees and shareholders on the supervisory board trade at a 31 stock market discount as compared with companies where employee representatives fill only one third of the supervisory board seats we show that under equal representation management board compensation provides incentives that are not conducive to furthering shareholders interests possibly because labor maximizes a different objective function than shareholders we document that under equal representation companies have longer payrolls than their one third representation peers have finally we provide evidence that shareholders respond to the allocation of control rights to labor by linking supervisory board compensation to firm performance and by leveraging up the firm jel g32 g34

commodity prices exchange rates and their relative volatility abstract exchange rates are move volatile than rates implied by ppp using conventional price indexes this fact has led many to believe that exchange rates fluctuate more than is warranted by the variability in commodity prices and supports those who believe that fluctuations in exchange rates are excessive we show that exchange rates are less volatile than commodity prices in auction markets and less volatile than rates implied by the law of one price using such prices we also show that the behavior of exchange rates and the rates implied by these commodity prices is not consistent with the dornbusch overshooting model

efficiency and internal organization works councils in west german firms efficiency voice theory has not explained why highly competent managers cannot maintain effective communication without formal or mandatory institutions of l abor s voice powerful west german works councils are negatively rela ted to productivity in the sample suggesting that the best managers can do better without councils however excessive pressure on worker s should encourage both unionization and councils to gain compensatin g differentials and the simultaneous wls tobit estimates also suppor t this effect general productivity benefits from formal voice organi zation are strongly rejected but evaluating welfare efficiency and causality directly requires data on job satisfaction and managerial ability copyright 1987 by the review of economic studies limited

works councils and employment growth in german establishments using data from german manufacturing establishments this article examines the relationship between works councils and employment growth taking the endogeneity of councils into account the estimates show a positive growth effect of works councils this suggests that the performance enhancing voice role of german works councils dominates their monopoly role moreover the findings of this study support the hypothesis that workers are more likely to implement a council to protect their quasi rents when the establishment is facing a long term crisis copyright the author 2009 published by oxford university press on behalf of the cambridge political economy society all rights reserved oxford university press

on the choice of incentives in firms abstract simple models of individual and group incentives under uncertainty are compared and comparative performance is shown to depend upon various exogenous parameters the incentive effects of profit sharing will thus vary with organizational and other characteristics that may be difficult to observe and attempts to quantify productivity effects that neglect selection bias are likely to be misspecified significant selection effects are found in previously used firm level data and productivity effects of existing profit sharing are found to be much larger than potential effects in firms without sharing arrangements this throws doubt on policies to encourage sharing in isolation

a note on simple criteria for optimal portfolio selection using sharpe s 7 single index model elton gruber and padberg egp 4 5 have established some simple ranking criteria for optimal portfolio selection a further extension has been made by chen and brown 2 and alexander and resnick 1 to incorporate the risk associated with the estimation of input parameters this note explores the economic rationale underlying the portfolio formation process based on the single index model in so doing we seek to enhance the intuitive appeal of the simplified portfolio criteria developed in the above studies to practitioners to this end we restate the egp solution with short sales allowed as

the empirical minimum variance hedge decision making under unknown true parameters estimation risk is discussed along with bayes and parameter certainty equivalent pce criteria bayes criterion incorporates estimation risk in a manner consistent with expected utility maximization the pce method which is the most commonly used is not consistent with expected utility maximization bayes criterion is employed to solve for the minimum variance hedge ratio empirical application of bayes minimum variance hedge ratio is addressed and illustrated simulations shoe that discrepancies between prior and sample parameters may lead to substantial differences between bayesian and pce minimum variance hedges

firm size efficiency and employment a review article s j s book contains much careful and interesting discussion of small firm employment data and related issues and will be read by all workers in the field however it also contains too much detailed quantification and international comparison of doubtful relevance at least for most economists and misses much background material of direct importance for evaluating the role of small firms as a result the authors seriously under estimate the contribution of small business to both employment and efficiency of modern economies as well as the importance of policy to correct the traditional and still pervasive bias towards large organizations

a note on market neutral portfolio selection abstract long short equity strategies allow investors to benefit potentially from both undervalued and overvalued securities the present study develops a normative portfolio model under the practical conditions that a market neutral strategy entails the offsetting long and short equity holdings are established jointly and without any constraints by the underlying market index while accurately capturing institutional procedures for short selling the model contains the analytical and economic properties as required for a ranking approach to filter out any undesirable securities under consideration in view of its practical features the analysis should be of interest to practitioners for assisting their long short investment decisions

portfolio analysis using single index multi index and constant correlation models a unified treatment in this study a simple common algorithm which is applicable to seven models is proposed for optimal portfolio selection disallowing short sales of risky securities the models considered in the analysis consist of a single index model four multi index models and two constant correlation models unlike the previous approach the proposed algorithm does not require explicit ranking of securities therefore it is particularly useful for two multi index models with orthogonal indices which do not provide any ranking criterion also because of its algorithmic efficiency as demonstrated in a simulation study on models with multiple groups the approach here can enhance their usefulness in portfolio analysis in a series of publications elton and gruber 2 and elton gruber and padberg hereafter egp 3 8 have considered extensively portfolio optimization problems using a variety of index models and constant correlation models these models are sharpe s 12 single index model cohen and pogue s 1 multi index model in the diagonal form a multi index model with orthogonal indices 8 a constant correlation model with a single group 3 and a constant correlation model with multiple groups 7 hereafter sim mim di mim or ccm s and ccm m respectively using these models egp have developed some ranking procedures to reach optimal portfolios disallowing short sales of risky securities all securities in each group are ranked according to their performance as measured by a ratio of excess return to risk they are sequentially added to feasible portfolios following the ranking hierarchy until the optimal portfolio is reached for models where explicit ranking criteria can be established the egp approach is easy to implement and it clearly explains why a security belongs or does not belong to a portfolio besides the above models it is also applicable to cohen and pogue s 1 multi index model in the covariance form hereafter mim co however it does not work well for models lacking appropriate criteria to rank securities in order to overcome ranking difficulties in mim or egp 8 have introduced a market portfolio with zero residual risk to establish an alternative ranking criterion unfortunately as egp have indicated this causes internal inconsistency in the analysis in the present study a simple algorithm for optimal portfolio selection disal

tests of three parity conditions distinguishing risk premia and systematic forecast errors abstract this study provides evidence that uncovered interest differentials between currencies cannot be attributed to either risk premia or systematic forecast errors alone the evidence is based on developing joint tests of three parity conditions uncovered interest parity purchasing power parity and real interest parity the study tests parameter restrictions based on knowing that risk premiums only affect nominal and real interest differentials but not inflation differentials while systematic errors in forecasting exchange rates only affect nominal interest differentials and inflation differentials but not real interest differentials the study finds a variety of cases where deviations from some or all of the parity conditions can be systematically related to variables currently known to investors and borrowers the most intriguing evidence is that for some currencies these deviations from parity are perfectly correlated as if they were driven by a common factor