a simple estimator for simultaneous models with censored endogenous reggressors this paper presents a simple two step estimator for models with censored endogenous regressors and sample selection bias the approach unifies the literature on censored endogenous regressors and sample selection bias and provides extensions the procedure employs generalized residuals to adjust for the inconsistency caused by the endogeneity of the censored regressors the paper also provides two new tests of weak exogeneity an empirical example examining the trade off between fringe benefits and wages indicates that the estimation procedure works well a monte carlo experiment suggests that the proposed tests have good power properties copyright 1993 by economics department of the university of pennsylvania and the osaka university institute of social and economic research association

does female education prevent the spread of hiv aids in sub saharan africa cross section estimates of 31 countries for the year 2000 are used to examine the effect of the level of female education and the gap between male and female levels on the prevalence of hiv aids in sub saharan africa many standard types of education are analysed and a non standard category involving under and over aged primary school enrollees are identified although it is found that female education is positively related to country infection rates there is scope to reduce infection rates by substituting one type of education for another it is estimated that female infection rates peak within 15 17 years of the first case reported

a general mean variance approximation to expected utility for short holding periods the mean variance model is precisely consistent with the expected utility hypothesis only in the special cases of normally distributed security returns or quadratic utility functions there is little evidence however that security returns follow normal distributions see 13 for references and quadratic preferences can be shown to generate implausible results exhibiting increasing absolute risk aversion in the pratt ll arrow 1 2 sense and displaying negative marginal utility after some finite wealth level in addition hakansson 4 has shown that single period mean variance efficient portfolios can have disastrous consequences over time even when return distributions are stationary such criticisms of the mean variance approach within the von neumann morgenstern framework have prompted several writers to suggest that investors maximize the expected value of utility functions with more realistic properties while others have criticized the single period focus of the model one popular alternative utility function is the logarithmic function which exhibits decreasing absolute risk aversion and conveniently leads to myopic decision processes through time i e investors treat each period as if it were the last basing investment decisions on that period s wealth and return distributions only 8 4 other utility functions with constant relative risk aversion such as the power function also imply myopic decision rules within a multiperiod setting

methods of pay and earnings a longitudinal analysis using data from the national longitudinal survey of youth 1988 90 the author investigates the relationship between methods of pay including piece rates and bonuses and the level and variance of wages among men piece rate workers earned a premium compared to other workers but the evidence on bonuses is mixed the author finds evidence that female piece rate workers earned more than other female workers once a control variable for the presence of dependents is interacted with the piece rate variable with controls for the wage effects of schooling and experience unobserved worker productivity is found to have accounted for most of the wage variance among both male and female piece rate workers wage variance among workers not having explicit pay for performance schemes in contrast was predominantly due to other factors

international portfolio choice and political instability risk a multi objective approach abstract the benefits derived from international portfolio diversification into foreign nations including the less developed countries are well documented yet this practice is discouraged due to market imperfections such as political instability in practice nations may be differentiated further by many aspects such as border controls or political and social trends which constrain private transactions and financial decisions this paper attempts to examine 1 whether the home asset bias in a portfolio holding is associated with higher political instability risk and 2 to what extent international diversification among stocks in the presence of such risk outperforms domestic stock portfolios using alternative instability risk proxies in the context of a discrete time version of mean variance framework we corroborate the impact of this type of risk on international portfolio investment decisions

effects of family background on earnings and returns to schooling evidence from brazil we investigate whether omitted family background variables are responsible for high returns to schooling estimated in brazil returns to schooling fall by about one third when parental schooling is added to wage equations surprisingly the schooling of fathers in law has larger effects on wages than the schooling of fathers on the basis of a model of assortative mating we interpret this as evidence that parental characteristics represent unobservable worker attributes rather than nepotism in the labor market we conclude that the family background bias in returns to schooling is modest and need not imply returns to family connections

railway development from the japanese occupation period to the present using kaohsiung city as an example abstractthis study intended to discuss the interactive influence of the emergence transformation and decline of the railway in kaohsiung port on urban development the population the activities and the economy in the region during the period of 1895 2010 from the perspectives of urban planning railway development population and industry this study used the crossover analysis method and used the factors of railway development and urban planning within a fixed time period to explore the chain dependence relationship among the industry the population the regional economy and the railway stations in kaohsiung city this study found that urban planning economic development railway development and industry have an interactive influence on the overall urban development urban planning promotes the rapid growth of the population and economic development propels the growth and shaping of the regional economy thus increasing employment opportunities in addition the railway development process moves

an alternative test of the capital asset pricing model reply in our 1980 paper we tested the joint hypothesis that prices are determined by the mean variance mv capital asset pricing model capm and that beliefs are stationary by focusing on the invariance law of prices we avoided the questionable practice of estimating ex ante expectations with ex post returns moreover we circumvented the need to identify the true market portfolio and hence avoided the ambiguity noted by richard roll 1977 in the traditional security market line sml tests of the same joint hypothesis however stuart turnbull and ralph winter t w and richard sweeney point to a further inconsistency in the joint hypothesis that they believe can be removed by relaxing the stationarity assumption this new concern is fundamental in that it applies to all empirical tests which assume stationarity of the return distribution whether they are simply tests of the capm or tests employing the capm the concern would apply a fortiori to tests that assume stationary betas as well both comments also suggest that the ad hoc addition of a random error term to our invariance law equation and the subsequent statistical tests of it are unnecessary we first address these two criticisms and then address some further criticisms raised separately by t w and sweeney

pricing and patents of hiv aids drugs in developing countries this article provides empirical evidence on the impact of patents on drug prices across developing countries it uses sales data on human immunodeficiency virus hiv acquired immuno deficiency syndrome aids drugs in a sample of 34 low and middle income countries between 1995 and mid 2000 the main findings are that patents do shift drug prices up drug prices are correlated to per capita income levels and drug firms follow a skimming strategy when pricing new hiv aids drugs that is there is across country and intertemporal price discrimination in the global drug markets

the returns to schooling a selectivity bias approach with a continuous choice variable the essence of selection bias is that we do not observe nonoptimal choices this applies whether the choice variable is discrete or continuous this paper extends the selection bias methodology to the case where the choice variable is continuous and the choice set is ordered the leading practical application of this analysis is the schooling choice problem schooling is treated as a continuous choice variable and selectivity corrected rates of return are estimated the findings suggest selectivity is of considerable importance and support the comparative advantage hypothesis of willis and rosen 18

macroeconomic consequences of the russian mortality crisis abstract this paper examines macroeconomic consequences of the russian mortality crisis life expectancy in russia decreased from 70 to 65 years during the first half of the 1990s which we estimate accounts for approximately 1 6 million excess deaths during 1990 1995 coupled with its disproportionate impact on working age males the large number of excess deaths suggests the crisis may have had a significant negative impact on the level and growth of russia s per capita income we estimate the economic cost of the crisis using two alternative approaches first we estimate the capitalized value of the income forgone due to the crisis which represents between 1 8 and 2 7 of russia s 1990 gdp there are however both theoretical and empirical problems with this approach to estimating the cost of the crisis second we estimate the parameters of a macroeconomic growth model and use it to calculate the effect of the crisis on russia s rate of economic growth our calculations suggest that the net effect of the drop in life expectancy the decline in the rate of total population growth and the even larger decline in the rate of growth of the working age population have been to lower the annual rate of growth of income per capita in russia by roughly one third of one percentage point given that russia s per capita income fell at an average annual rate of 9 during 1990 1995 we conclude that the mortality crisis which has unquestionably been catastrophic in human terms has been at most a small contributor to russia s poor macroeconomic performance the paper also discusses the effects of the crisis on other macroeconomic variables such as income inequality and the fiscal balance of the pension system the paper concludes with a discussion of possible new approaches to modeling the two way linkages between health status and economic growth

partial monitoring adverse selection and the internal efficiency of the firm abstract the paper investigates an adverse selection model with monitoring of managerial effort in contrast to the literature we assume that the manager can be punished only if his effort is below a certain level that is monitored by the principal surprisingly the optimal labor contract may induce an equilibrium effort which is lower than in the standard model without monitoring this result holds for any discrete distribution of managerial types in the continuous type case the optimal contracts for high quality low quality managers are purely output dependent effort dependent

the mean variance optimization puzzle security portfolios and food portfolios the markowitz mean variance optimization framework presents a puzzle although it is the standard model of portfolio construction investors rarely use it and when used it is constrained so much that portfolios reflect the constraints more than the optimization why do investors dislike unadulterated optimized mean variance portfolios the typical answer focuses on biases introduced by estimation errors more important is the fact that investors goals are quite different from mean variance optimization people care about more than cost and nutrition when they construct their diets they also care about palatability similarly investors care about more than expected returns and variance as they construct their securities portfolios they also care about the investment equivalent of palatability we use an analogy between security portfolios and food portfolios to explore the nature of the gap between intuitively appealing portfolios and mean variance optimized portfolios

normality solvency and portfolio choice this paper examines whether investors with power utility functions choose mean vari ance mv efficient portfolios when returns are approximately normally distributed and there is borrowing or lending at a riskless interest rate the results show that the unlevered portfolios of power utility investors plot very closely to the mv efficient frontier how ever there are marked differences in the mix of risky assets regardless of whether the portfolios are highly concentrated or widely diversified such differences allow power investors to remain solvent even when they lever their optimal portfolios to a greater ex tent than less risk averse mv investors who risk bankruptcy it is concluded that the investment policies of power utility and mv investors with similar risk aversion measures are not as similar as is commonly believed this is particularly true for high power inves tors unless explicit solvency constraints are imposed on the mv problem and for low power investors when quadratic utility approximations are made to the power utility func tions these differences in the investment policies of power utility and mv investors lead us to question the widely accepted assertion that the assumptions of homogeneous beliefs normality a riskless asset and risk averse investors imply the simple mv capm where all investors including power utility investors hold combinations ofthe market portfolio and the riskless asset

on the sensitivity of mean variance efficient portfolios to changes in asset means some analytical and computational results tbis paper investigates the sensitivity of meanvariance mv efficientportfolios to changes in the means of individual assets when only a budget constraint is imposed on the investment problem the analytical results indicate that an mv efficient portfolio s weights mean and variance can be extremely sensitive to cbanges in asset means when nonnegativity constraints are also imposed on the problem the computational results confirm that a positively weigbted mv efficient portfolio s weigbts are extremely sensitive to cbanges in asset means but the portfolio s returns are not a surprisingly small increase in the mean of just one asset drives balf the securities from the portfolio yet the portfolio s expected return and standard deviation are virtually uncbanged this paper supersedes should investors hold well diversified portfolios financial support from the natural science and engineering research council of canada is gratefully acknowledged we also acknowledge the most capable assistance of ruth cornale simon ng jean marc potier and frederick shen the paper was presented at simon fraser university and the western finance association meetings in san diego we thank the participants especially stephen brown john herzog john heaney ray koopman and bruce lehmann and the editors jon ingersoll and chester spatt for

high and declining prices signal product quality high and declining prices signal a high quality product high prices are the efficient means of signaling because the consequent loss of sales volume is most damaging for lower cost lower quality products as time passes and the number of informed consumers increases the signaling distortion lessens resulting in a declining price profile the prediction of high and declining prices is robust across a variety of dynamic models and is consistent with recent empirical findings copyright 1991 by american economic association

hiv status and labor market participation in south africa abstract we use econometric methods based on the propensity score to estimate the causal effect of hiv status on employment outcomes in south africa relying on rich data from a national survey which included hiv testing we control for systematic differences between hiv positive and hiv negative individuals we provide the first nationally representative estimates of the impact of hiv status on employment outcomes for southern africa being hiv positive is associated with an increase of 6 to 7 percentage points in the likelihood of unemployment overall and 10 to 11 percentage points for those who are less educated this disadvantage reinforces existing inequalities in south africa

information marketing and pricing in the u s antiulcer drug market introduced into the united states in 1977 tagamet was the pioneer product in the class of antiulcer drugs known as h2antagonists by promoting ulcer healing through inhibiting acid secretion tagamet was able to heal ulcers and treat pre ulcer conditions pharmacologically on an outpatient basis thereby substituting for more costly hospital admissions and surgeries in 1983 another h2 antagonist called zantac entered and by early 1987 u s zantac sales surpassed those of the pioneering tagamet today there are four h2 antagonists sold in the united states tagamet zantac pepcid and axid zantac is now the world s largest selling prescription drug having estimated worldwide sales in 1994 of about 4 billion each of the four h2 antagonists is among the top 100 in world drug sales although tagamet lost u s patent protection on may 17 1994 in this paper we examine empirically the role of information in facilitating and explaining growth of the overall antiulcer drug market as well as in shaping the changing market shares of the four patented products the dissemination of information is due largely to the use of marketing channels such as visits by manufacturers representatives to physicians called detailing advertising in medical journals and most recently by direct to consumer advertising we examine these and also explore pricing policies product differentiation and orderof entry effects

unobserved ability efficiency wages and interindustry wage differentials interindustry wage differentials in wage regressions estimated for individuals have been interpreted as evidence consistent with efficiency wage models a principal competing explanation is that these differentials are generated by differences across workers in unobserved ability this paper tests the unobserved ability hypothesis by incorporating test scores into standard wage regressions as error ridden indicators of unobserved ability the results indicate that differences in unobserved ability explain relatively little of interindustry or interoccupation wage differentials this abstract was borrowed from another version of this item

further results on the macroeconomic effects of aids the dualistic labor surplus economy this article generalizes and extends the earlier analyses of cuddington 1993 and cuddington and hancock forthcoming by incorporating the presence of underemployment and dual labor markets considerations that seem particularly important when assesssing the likely impact of aids in many african countries the dual economy simulations of the economic impact of aids using tanzanian data suggest that the macroeconomic consequences of the epidemic are of the same order of magnitude as those obtained using a single sector full employment model gross domestic product gdp is 15 to 25 percent smaller by 2010 than it would have been wtihout aids and per capita gdp is 0 to 10 percent smaller the output loss from aids in the dual economy framework is roughly the same as the output gain achievable through policies designed to increase labor market flexibility the exercise is crude but it suggests that meaningful efforts at economic reform in economies devastated by aids may at least ameliorate some of the negative economic effects of the epidemic although they would certainly not offset its personal and social costs

consumption externalities and diffusion in pharmaceutical markets antiulcer drugs we examine the role of consumption externalities in the demand for pharmaceuticals at both the brand level and over a therapeutic class of drugs externalities emerge when use of a drug by others affects its value and or conveys information about efficacy and safety to patients and physicians this can affect the rate of market diffusion for a new entrant and can lead to dominance of one drug despite the availability of close substitutes we use data for h2 antagonist antiulcer drugs to estimate a dynamic demand model and quantify these effects the model has three components an hedonic price equation that measures how the aggregate usage of a drug as well as conventional attributes affect brand valuation equations relating equilibrium market shares to quality adjusted prices and marketing levels and diffusion equations describing the dynamic adjustment process we find that consumption externalities influence both valuations and rates of diffusion and that they operate at the brand and not the therapeutic class level

the long run economic costs of aids a model with an application to south africa primarily a disease of young adults acquired immuno deficiency syndrome aids imposes economic costs that could be devastatingly high in the long run by undermining the transmission of human capital the main driver of long run economic growth across generations aids makes it harder for victims children to obtain an education and deprives them of the love nurturing and life skills that parents provide these children will in turn find it difficult to educate their children and so on an overlapping generations model is used to show that an otherwise growing economy could decline to a low level subsistence equilibrium if hit with an aids type increase in premature adult mortality calibrating the model for south africa where the hiv prevalence rate is over 20 percent simulations reveal that the economy could shrink to half its current size in about four generations in the absence of intervention programs to combat the disease and to support needy families could avert such a collapse but they imply a fiscal burden of about 4 percent of gross domestic product gdp

bayesian estimation of the global minimum variance portfolio in this paper we consider the estimation of the weights of optimal portfolios from the bayesian point of view under the assumption that the conditional distribution of the logarithmic returns is normal using the standard priors for the mean vector and the covariance matrix we derive the posterior distributions for the weights of the global minimum variance portfolio moreover we reparameterize the model to allow informative andnon informative priors directly for the weights of the global minimum variance portfolio the posterior distributions of the portfolio weights are derived in explicit form for almost all models the models are compared by using the coverage probabilities of credible intervals in an empirical study we analyze the posterior densities of the weights of an international portfolio

earnings productivity and performance related pay jobs with performance related pay prp attract workers of higher ability and induce workers to provide greater effort we construct an integrated model of effort and sorting that clarifies the distinction between observable and unobservable ability and the relationship between earnings and productivity predictions are tested against data from the british household panel survey bhps the prp raises wages by 9 for men and 6 for women theoretical calculations show that these estimated earnings differentials represent average productivity differentials net of monitoring costs at the marginal firm using prp but not of the disutility of additional effort expended by workers

returns to endogenous education the case of honduras the rapid expansion of the education sector in developing countries and the scarcity of public funds have increased the need for an accurate evaluation of educational policies estimates of rates of return to education have often been used as an integral part of cost benefit studies and programme evaluation efforts this study uses household survey data from honduras for 1990 to estimate returns to education that allow for worker heterogeneity and individual self selection in the education process a sequential estimation procedure is used that enables study of the interaction between educational attainment and earnings determination it is found that accounting for endogenous educational attainment leads to substantially higher estimated returns to education compared to traditional least squares estimates the possible magnitude of the bias underscores the importance of recognizing the role of self selection and comparative advantage in the education process

adult mortality and consumption growth in the age of hiv aids the authors use a 13 year panel of individuals in tanzania to assess how adult mortality shocks affect both short and long run consumption growth of surviving household members using unique data which tracks individuals from 1991 to 2004 they examine consumption growth controlling for a set of initial community household and individual characteristics the effect is identified using the sample of households in 2004 which grew out of baseline households the authors find robust evidence that an affected household will see consumption drop 7 percent within the first five years after the adult death with high growth in the sample over this time period this creates a 19 percentage point growth gap with the average household there is some evidence of persistent effects of these shocks for up to 13 years but these effects are imprecisely estimated and not significantly different from zero the impact of female adult death is found to be particularly severe

aids crisis and growth abstract we investigate an olg economy where an aids epidemic influences human capital accumulation and growth through the creation of large numbers of orphans we study how intra family allocations regarding school and work time of children are adjusted in the face of aids within a family and how in turn these adjustments influence accumulation of physical and human capital we compute the aggregate effects of an aids epidemic on human and physical capital accumulation and growth we find that growth effects of an aids epidemic are large some policies such as subsidization of aids medication have relatively small effects

strategic pricing of new pharmaceuticals this paper provides empirical evidence on the leading factors affecting the prices of new pharmaceuticals both at introduction and after 4 6 and 8 years most important is the extent of therapeutic advance embodied in a new product for drugs which represent important therapeutic gains launch prices can be two or three times those of existing drugs used for the same purposes while drugs that largely duplicate the actions of currently available products are typically priced at comparable levels in addition the number of branded substitutes has a substantial negative effect on launch prices which reflects the importance of competitive pressures duplicate products thereby play an important economic role in pharmaceutical markets

occupational social value and returns to long hours this paper examines the phenomenon of uncompensated long hours in jobs with pro social characteristics and presents evidence that long hour wage premiums and occupational social value are substitutes in compensating salaried workers who supply hours exceeding the standard working week i show that the social value of an occupation in particular the degree to which jobs involve helping or providing service to others is inversely related to long hour pay allowing for heterogeneity in the degree to which workers value their job s helping orientation lets me explore how gender differences in employees attitudes toward pro social behaviour can explain some of the observed occupational sorting trends and gender differences in long hour compensation women tend to be more strongly drawn to helping occupations and at the same time receive lower long hour premiums in these jobs relative to men i offer a theoretical framework to rationalize the empirical trends

pricing dynamics in the pharmaceutical industry pricing behaviour has traditionally been approached from the concept of long term static equilibrium this paper argues that this approach is inappropriate at least with respect to the pharmaceutical market because new innovation and patent expiry lead to a continually changing environment a theoretical analysis argues that price change will depend on the age of the therapeutic class the degree of brand loyalty the extent to which it is sold over the counter rather than on prescription and measures of competition the empirical results based on an analysis of the leading twenty five therapeutic class of pharmaceuticals in the usa the uk west germany and france over the period 1981 1988 tends to support the theoretical conclusions although it would appear that government controls in the uk are distorting profit maximizing behaviour more than in the other three countries

how much of a threat to economic growth is a mature aids epidemic the article models the impact on economic growth of hiv aids when the epidemic is in a mature phase in contrast with previous studies focused on periods of expansion as it is typically the case in african countries simulations for honduras the epicentre of the epidemic in central america show that aids is not likely to threaten economic growth neither through labour nor capital accumulation channels impacts are estimated between 0 007 and 0 27 points of gross domestic product gdp growth annually for the period 2001 to 2010 increasing spending on prevention higher public treatment subsidies and increasing treatment access will not jeopardize economic growth prospects critical factors that slash economic growth in africa such as human capital reductions and shifts in relative skills are not strong in honduras

pharmaceutical patents prices and welfare losses policy options for india under the wto trips agreement c oncerns on the effect of product patents on the prices of medicines have been acute in many developing countries which up to the entry into force of the world trade organisation wto agreement on trade related aspects of intellectual property rights trips in 1995 could and did disallow such patenting in their national patent laws with trips all members of and those seeking accession to the wto have to make available with limited exceptions both product and process patents in every sector including pharmaceuticals more specifically trips provides that all wto members have to receive product patent applications for pharmaceuticals from the date of establishment of the wto i e january 1995 it is important to note that even under the trips regime patents are to be granted only on applications received from 1995 onwards for new patentable pharmaceutical inventions thus prices of existing pharmaceuticals already on the market or even those covered by patent

pricing profits and technological progress in the pharmaceutical industry the decades old debate over pharmaceutical industry prices profits and innovation has again intensified a number of events coalesced to refocus public interest on pharmaceuticals contributing to public concern were bureau of labor statistics price index increases for pharmaceuticals far outpacing those for the products of other industries another prominent characteristic of the pharmaceutical industry has been its extraordinarily high reported profitability this article examines the phenomena that precipitated the current pharmaceuticals debate their historical antecedents and the principal questions at issue in the author s considered judgment a pell mell march toward regulation of pharmaceutical industry pricing could seriously impair the industry s incentives for investment in new products

there is no silver bullet the value of diversification in planning invasive species surveillance abstract in this study we demonstrate how the notion of diversification can be used in broad scale resource allocation for surveillance of invasive species we consider the problem of short term surveillance for an invasive species in a geographical environment we find the optimal allocation of surveillance resources among multiple geographical subdivisions via application of a classical portfolio framework which allocates investments among multiple financial asset types with uncertain returns in a portfolio that maximizes the performance and by meeting the desired diversification targets protects against errors in estimating the portfolio s performance we illustrate the approach with a case study that applies a spatial transmission model to assess the risk of spread of the emerald ash borer eab a significant pest in north america with infested firewood that may be carried by visitors to campground facilities in central canada adding the diversification objective yields an expected survey performance that is comparable with undiversified optimal allocation but more importantly makes the geographical distribution of survey priorities less subject to possible errors in the spread rate estimates overall diversification of pest surveillance can be viewed as a viable short term strategy for hedging against uncertainty in expert and model based assessments of pest invasion risk

60 years of portfolio optimization practical challenges and current trends abstract the concepts of portfolio optimization and diversification have been instrumental in the development and understanding of financial markets and financial decision making in light of the 60 year anniversary of harry markowitz s paper portfolio selection we review some of the approaches developed to address the challenges encountered when using portfolio optimization in practice including the inclusion of transaction costs portfolio management constraints and the sensitivity to the estimates of expected returns and covariances in addition we selectively highlight some of the new trends and developments in the area such as diversification methods risk parity portfolios the mixing of different sources of alpha and practical multi period portfolio optimization

do national patent laws stimulate domestic innovation in a global patenting environment a cross country analysis of pharmaceutical patent protection 1978 2002 this paper evaluates the effects of patent protection on phar maceutical innovations for 26 countries that established pharmaceutical patent laws during 1978 2002 controlling for country characteristics through matched sampling techniques to establish two proper comparison sets among 92 sampled countries and through country pair fixed effects regressions this study yields robust results national patent protection alone does not stimulate domestic innovation as estimated by changes in citation weighted u s patent awards domestic r d and pharmaceutical industry exports however domestic innovation accelerates in countries with higher levels of economic development educational attainment and economic freedom additionally there appears to be an optimal level of intellectual property rights regulation above which further enhancement reduces innovative activities

how many stocks make a diversified portfolio we show that a well diversified portfolio of randomly chosen stocks must include at least 30 stocks for a borrowing investor and 40 stocks for a lending investor this contradicts the widely accepted notion that the benefits of diversification are virtually exhausted when a portfolio contains approximately 10 stocks we also contrast our result with the levels of diversification found in studies of individuals portfolios

portfolio selection under distributional uncertainty a relative robust cvar approach robust optimization one of the most popular topics in the field of optimization and control since the late 1990s deals with an optimization problem involving uncertain parameters in this paper we consider the relative robust conditional value at risk portfolio selection problem where the underlying probability distribution of portfolio return is only known to belong to a certain set our approach not only takes into account the worst case scenarios of the uncertain distribution but also pays attention to the best possible decision with respect to each realization of the distribution we also illustrate how to construct a robust portfolio with multiple experts priors by solving a sequence of linear programs or a second order cone program

the impact of aids on income and human capital this paper studies the impact of hiv aids on per capita income and education it explores two channels on how hiv aids affects income that have not been sufficiently stressed by previous literature the reduction of the incentives to stay in school due to shorter expected longevity and the reduction in productivity of experienced workers in the model individuals live for three periods may get infected in the second period and with some probability die of aids before reaching the third period of their lives parents care for the welfare of the future generations so that they will maximize lifetime utility of their dynasty the simulations predict that the most affected countries in sub saharan africa in the future will be on average 30 poorer than they would be without aids schooling will decline in some cases by 40 these figures are dramatically reduced with widespread medical treatment as it increases the survival probability and productivity of infected individuals

pricing patent loss and the market for pharmaceuticals dustry the drug price competition and patent term restoration act of 1984 very clearly reflects the determination of policy makers to simultaneously address issues of price control and technical progress the 1984 act increased returns to innovation by extending the period of patent protection to take into account the time between receipt of a patent and food and drug administration fda approval of a drug for sale in the market the 1984 act also reduced the testing requirements for approval of new generic brands of existing chemical entities thus reducing entry barriers in markets where patents have expired the expected outcome from eased entry conditions for generic substitutes was substantially enhanced price competition and lower prices for brand name drugs in fact prices for brand name drugs have tended to increase following entry by generics wagner and duffy 28 examined price changes for top selling generics and name brands they show substantial price increases in brand name prices accompanying large reductions in generic prices as entry of generics occurs grabowski and vernon 9 examined data on 18 major orally administered rug products subject to generic competition between 1983 and 1987 and found that the name brand price increased by an average of 7 one year subsequent to generic entry and 11 two years following generic entry

auditing the producer price index micro evidence from prescription pharmaceutical preparations from january 1984 through december 1989 the bureau of labor statistics bls price index for prescription pharmaceuticals grew at 9 09 per year using bls type laspeyres index procedures with monthly price and quantity data on all prescription pharmaceuticals sold by four u s pharmaceutical manufacturers accounting for 24 of industry domestic sales we find that the four company index increases at 6 68 per year when we employ a divisia price index with smoothed weights incorporating new goods the index grows 6 03 per year why does the bls index grow 50 more rapidly than the divisia index that mystery is the focal point of our article

portfolio analysis an analytic derivation of the efficient portfolio frontier abstract in this paper the efficient portfolio frontier is derived explicitly for cases in which short sales are not allowed when all securities are risky it is shown that the efficient portfolio frontier consist of a series of monotonously increasing arcs of convex parabolas in the return variance plane if the efficient portfolio frontier of risky securities are known the efficient frontier can easily be revealed when there is a riskless security an upper limit on borrowing is also introduced

firms choice of method of pay using data from the bls industry wage survey the author tests the theory that firms choose their methods of pay by balancing the gains from more precise links between performance and pay against m

brazil widening the scope for balanced growth abstract the paper explores issues bearing upon the growth process in brazil assessing the importance of constraints on growth and the scope of government policies designed to attenuate them in the coming years the workings of the economy are described in a simple model which highlights how trade liberalization the new pattern of public spending and environmental conservation policies may affect growth possibilities medium term prospects are examined using the model first without considering the effects of environmental policies and then taking them into account

wages and performance based pay evidence from the nlsy abstract the link between performance and pay should be strongest where performance is more accurately observed brown industrial and labor relations review 1990 43 1655 1825 rand journal of economics 1992 23 366 375 more productive workers self select into jobs with performance based pay consequently workers whose pay is based on performance should earn more than those whose pay is not based on such measures this paper adds to the literature on the subject by providing new empirical evidence for brown s model using the national longitudinal surveys of youth nlsy data

the effect interruptions in work experience have on wages individuals who interrupt their employment are generally expected to pay a price in the workplace 15 most researchers acknowledge that wages rise more rapidly with time spent in paid employment than with time spent in other noneducational activities thus the wages received by individuals reentering employment are expected to be below those obtained by similar individuals with continuous work records how far below is still a matter of debate one important line of research has focused upon the difference between pre interruption and post interruption wages specifically do real wages rise fall or remain unchanged during periods of nonemployment two findings stand out from past research first a wide variety of studies employing a wide variety of data sets have found that wages fall during periods of nonemployment the estimated decline ranges from 0 6 to over 5 annually but averages around 2 second this estimated depreciation rate is higher when the sample under investigation contains a greater proportion of recent reentrants thus there is a pattern to the estimates the purpose of this study is to investigate the observed sensitivity to sample composition in the past such sample sensitivity has been attributed to a rapid depreciation followed by a rebound in wages that over time partially offsets the initial decline if true the depreciation rate will be underestimated especially if the data include few recent reentrants two alternative hypotheses are tested in this study the first relies upon certain assumptions regarding part time employment patterns and wages if part time workers are paid less than full time workers and if part time employment is more common following reentry because it is used as a bridge to full time employment then estimates of the depreciation rate will be biased upward particularly when obtained from samples of recent reentrants if information on hours worked is ignored there may in fact be no depreciation at all results indicate that while part time workers are paid less than full time workers estimates

assessing the impact of aids on the growth path of the malawian economy abstract a modified solow growth model is used to simulate the impact of the aids epidemic on output capacity and other key macroeconomic aggregates in malawi comparing a counterfactual no aids scenario to medium and extreme aids projections suggests that average real gdp growth over the 1985 2010 period will be 0 2 0 3 1 2 1 5 percentage points lower in the medium extreme case relative to the no aids case as a result the size of the economy by the year 2010 will be reduced from a real gdp of 5 03 billion constant 1985 kwacha without aids to 4 81 4 77 3 80 3 46 billion kwacha in the medium extreme scenario

the effect on black white wage differences of differences in the quantity and quality of education using data from the national longitudinal survey of youth for the years 1979 88 the author examines the extent to which black white differences in educational attainment educational quality and unmeasured individual ability can explain black white wage differences an analysis that corrects for both selectivity and ability biases inherent in estimating the education wage relationship shows that the main source of the black white wage differential is the racial difference in the quality rather than quantity of schooling in fact the author concludes closing the racial gap in the basic skills learned in school could reduce the wage differential by two thirds

parental childcare and children s educational attainment evidence from china this paper examines the determinants of child educational attainment in addition to those examined in previous studies it is found that maternal childcare is another important determinant of child educational attainment the results are robust after controlling for endogeneity the iv estimates show that once childcare time is controlled for child health does not have an effect on school enrolment age this finding suggests that omitting the childcare time may have biased the estimated effect of child health on school enrolment in previous studies

educational attainment and earnings determination in colombia the expansion of the education sector in developing countries since the mid 1950s is certainly impressive between 1950 and 1980 primary and secondary enrollment ratios in many of these countries tripled or quadrupled and the educational gap with respect to developed countries narrowed although most social planners and politicians would argue that there is still a long way to go before socially optimal levels of education are attained it is also commonly acknowledged that there is an increasing need for a more careful and systematic evaluation of educational policies and by implication public funding priorities 2 although there is the question of whether all types of education should be considered equally much of the work in the evaluation process has been devoted to the production of estimates of the social and private rates of return to schooling 3 most of the early research in this area ignored the effects of educational quality heterogeneous individual abilities and other types of selection bias issues these so called first generation models produced relatively high rates of return to additional years of education from 15 to 30 depending on the country and statistical methodology employed 4 these estimates led to a form of consensus that education was a high priority item in government budget planning there is only limited evidence of how rates of return have fared subsequent to the growth of the education sector in the case of colombia however g psacharopoulos noted that the rate of return to education fell from about 20 in the early sixties to below 10 by 1979 5 during the eighties a number of second generation studies

aggregate price indices new goods and generics this paper examines the appropriate treatment in the cost of living index of the appearance of new varieties of old goods existing theory here applies to individual households thus we first show in what sense laspeyres and paasche indices for groups of households can be considered approximations to theoretically desirable group indices and then go on to the case of new goods we apply our results to the case of the introduction of generics in pharmaceuticals and show that proper treatment can make a considerable difference

generics and new goods in pharmaceutical price indexes drug prices and their rate of inflation are a major focus of current policy debates on u s health care in this paper we show that where patent expiration and generic entry are significant as they are for many important classes of drugs movements in the official price indexes may be poor indicators of the actual prices paid and the resulting changes in consumer welfare when a drug goes off patent those consumers who regard the branded and generic versions as more or less perfect substitutes experience a substantial price decline and concomitant welfare gain which the current methods used by the statistical agencies fail to capture we suggest a number of alternative ways of proceeding although our computations are based on a limited number of cases they imply that the overall rate of inflation in drug prices may be quite seriously overstated while generic pharmaceuticals are the topic of our calculations the problem discussed is also of wider importance generic drugs are a special and possibly easy case

why do diplomas pay an expanded mincerian framework applied to mexico we compare four explanations for the value of diplomas each of which has implications for unemployment and wage variation amongst graduates most of which have not previously been tested for when seeking to explain the effects of diplomas we test for these implications using a refined econometric framework exploiting idiosyncrasies in mexican labour market and educational institutions premiums in mexico appear to result from diplomas tied to jobs with downwards rigid wages an uncommon but simple explanation the standard explanations including screening are not suggested by mexican data our results illuminate how labour markets segmented by diplomas clear this depends upon the nature of the labour market rigidities exactly as predicted by neoclassical theory

hiv aids and development a reappraisal of the productivity and factor accumulation effects besides the dreadful direct effects enduring epidemics like hiv aids induce much more subtle effects in the economy principally via labor productivity and factor accumulation concerning the former the impact of morbidity on effective labor has been recognized and accounted for since the early work of over 1992 and cuddington and hancock 1994 the impact of mortality shocks on savings and therefore on factor accumulation has also been documented in this early literature with an emphasis on the detrimental role of the induced health expenditures recently asiedu jin and kanyama 2015 show that hiv aids has a negative but diminishing effect on foreign direct investment fdi and this adverse effect occurs even when the prevalent hiv rate is low in contrast the consequences of hiv aids on human capital accumulation have been more rarely treated in particular its impact on schooling time n generally omitted in the macroeconomic literature ferreira pessoa and dos santos 2011 is an exception the inherent mechanism is known as the ben porath mechanism ben porath 1967 a downward trend in life expectancy following mortality shocks reduces the profitability of schooling leading to a decline of human capital accumulation in the medium and long run boucekkine de la croix and licandro 2002 have proposed a theory of endogenous growth based on the ben porath mechanism notice also that the same essential argument that shorter time horizons discourage investment can be applied to physical capital accumulation the latter may collapse not only because of the massive increase in health expenditures undermining savings as in the early literature but also via this indirect mechanism both channels are taken into account by freire 2004 in her analysis of saving behavior in south africa after the outbreak of the hiv aids crisis

wage levels and method of pay the traditional literature on method of pay distinguishes workers who are paid time rates from those who are paid piece rates the theory predicts that the piece rate workers will earn more and empirically they do a simple generalization is to divide time rate workers into two groups those whose wage depends on their supervisor s ratings and those whose wage does not theory predicts that the workers whose pay is linked to supervisor ratings will earn more than the other time rate workers wage data for workers in over 3 000 manufacturing establishments show they do not and several simple explanations fail to resolve this empirical puzzle

a possibilistic mean semivariance entropy model for multi period portfolio selection with transaction costs abstract this paper deals with a multi period portfolio selection problem with fuzzy returns a possibilistic mean semivariance entropy model for multi period portfolio selection is presented by taking into account four criteria viz return risk transaction cost and diversification degree of portfolio in the proposed model the return level is quantified by the possibilistic mean value of return the risk level is characterized by the lower possibilistic semivariance of return and the diversification degree of portfolio is measured by the originally presented possibilistic entropy furthermore a hybrid intelligent algorithm is designed to obtain the optimal portfolio strategy finally the comparison analysis between the possibilistic entropy model and the proportion entropy model is provided by two numerical examples to illustrate the efficiency of the proposed approaches and the designed algorithm

an analytic derivation of admissible efficient frontier with borrowing the admissible efficient portfolio selection problem for risky assets has been discussed by zhang and nie in this paper the admissible efficient portfolio model is proposed under the assumption that there exists the borrowing money or a risk free asset case the admissible efficient frontiers are developed by the spreads of expected return and risk from admissible errors the analytic forms of the admissible efficient frontiers when short sales are not allowed on all risky assets are derived from two cases the borrowing with an upper bound constraint or without an upper bound constraint the influence on the admissible efficient frontier is explained under the different interest rates of the borrowing the differences between the results with the borrowing and the results without the borrowing is revealed by a real numerical example

aids and economic growth a human capital approach abstract using a model that combines growth and health capital equations this study analyses the impact of hiv aids on economic growth the econometric results indicate that the epidemic s effects have been substantial in africa the marginal impact on income per capita of a 1 increase in hiv prevalence rate is minus 0 59 even in countries with lower hiv prevalence rates the marginal impacts are non trivial hence while the human and social costs of the hiv aids epidemic are major causes for concern these results indicate that the macroeconomic affects of the hiv aids epidemic are important

capital asset pricing compatible with observed market value weights we show that the set of expected return vectors for which an observed portfolio is mean variance mv efficient is a two parameter family we identify ten ways to specify the time series behavior of the two parameters the result highlights a number of inconsistencies involved in mv modelling for each of the cases it permits the inference of the time series of expected return vectors as well as all the other capital asset pticing model capm variables compatible with a known covariance matrix and the observed time series of market value weights the empirical work shows that there are substantial case to case differences in the time series of mean vectors and many of them are quite different from the constant mean vector envisioned in tests of

an investigation of the labor market earnings of panamanian males evaluating sources of inequality this paper presents empirical evidence on the determinants of labor market earnings and inequality for males in panama using newly available microdata we estimate earnings equations based on the measurement framework of mincer 1974 and compare them with those for other countries at various stages of economic development we present evidence on two aspects of inequality in less developed economies labor market segmentation and social stratification we present tests of the segmentation hypothesis including several of the dual labor market hypotheses and discuss their inherent ambiguity we also present evidence on the importance of family background for earnings determination and educational attainment

uncertain lifetime risk aversion and intertemporal substitution abstract this paper describes a simple utility function for dynamic choice problems under uncertain lifetime preferences are time consistent and similar to selden s ordinal certainty equivalent hypothesis for yaari s model of consumption savings decisions holding intertemporal substitution fixed the consumption growth rate is increasing decreasing in the mortality rate if risk aversion is lower higher than under expected utility preferences

the trade off between supervision cost and performance based pay does gender matter the study adds to the literature by providing new empirical evidence consistent with efficiency wage theory and by providing estimates of the average cost of supervising a worker by industry this research uses the 1996 wave of the nlsy and incorporates estimates of supervision cost computed from industry classifications we further detect presence of no gender differences neither in risk averseness nor in productivity gains associated with cost of supervision and performance based pay while the findings imply that employers should consider the incentive effects of supervision and performance based pay when constructing pay schemes there is no need for employers to devote resources to constructing gender specific payment mechanisms our evidence suggests that profit maximizing firms should treat males and females equally and develop gender neutral pay schemes

education policy reform local average treatment effect and returns to schooling from instrumental variables in the philippines a nationally representative dataset from the philippines is used to derive returns to schooling estimates from instrumental variables utilizing a supply side intervention in the education market capable of generating significant changes in schooling these estimates apply to a subgroup of mainly liquidity constrained individuals in the spirit of the local average treatment effect late literature returns to schooling estimates which apply to a subgroup of individuals affected by policy intervention may be more interesting from a policy perspective than the return to the average individual the findings are consistent with other recent evidence suggesting that the causal effect of education at least for certain subgroups of individuals is as big or bigger than what is suggested by ols estimates

improving diversification opportunities for socially responsible investors socially responsible investment sri has grown enormously and has expanded globally in recent years it allows sri investors to reduce their portfolio risk assumptions through international diversification in this context the aim of this paper is twofold i to examine price and volatility linkages among the most representative sri indexes for north america europe and asia pacific employing a multivariate approach and ii to provide the out of sample performance of an optimal portfolio constructed on the basis of time varying return and volatility forecasts from this specification approach our overall results show that using this technique it is possible to reduce risk and out perform the naive rule which is usually employed in this type of investment these findings are relevant not only for academics but also for practitioners especially for professional managers of sri portfolios

a cost benefit analysis of female primary education as a means of reducing hiv aids in tanzania this article uses panel data related to 20 tanzania regions and 8 years to estimate the direct and indirect effects of female primary education on hiv aids rates a recursive framework for education income and infections is employed based on two autoregressive equations that allow us to obtain dynamic estimates of effectiveness we find that the indirect effect working through changes in income outweighs the direct positive effect of education on infections implying that female education can be effective as an intervention to lower the disease in tanzania the estimates of effectiveness are then utilized to carry out a cost benefit analysis of the education expenditures the human capital approach is used to measure the benefits irrespective of the timing of the benefits and costs and the discount rate alternatives we consider our best estimates result in positive net benefits with benefit cost ratios in the range 1 3 2 9 this article was completed with the financial assistance provided by the

modeling the macroeconomic effects of aids with an application to tanzania a solow style model is developed to study the effects of the aids epidemic on the growth path of the economy and gdp per capita the model uses conjectures about the demographic effects of aids in tanzania to estimate the macroeconomic effects on the economy the findings suggest that without decisive policy action aids may reduce tanzanian gdp in the year 2010 by 15 to 25 percent in relation to a counterfactual no aids scenario per capita income levels are expected to fall by 0 to 10 percent by 2010

the quality of schooling quantity alone is misleading although much research discusses the quantity of schooling as an effective impact on productivity and earnings most such research leaves out the idea of the quality of schooling which may cause biases in the estimated returns to schooling this paper consequently attempts to extend the standard mincerian approach to incorporate school quality as well as quantity it demonstrates how exclusion of quality in the standard procedure may cause biases in the estimated returns to years of schooling probably in the upward direction the paper explores the implications of this extension of the standard model for the case of young brazilian males it shows that the estimate of the private return to years of schooling using the preferred quality inclusive specification is only one half the estimate using the standard procedure indicating substantial upward bias in the standard estimates it further outlines a method for estimating a social return to quality and finds that it exceeds substantially the social return to quantity the paper then shows why this in turn suggests there may be an equity productivity trade off in schooling investments

earnings schooling ability and cognitive skills conventional estimates now available for a large number of countries generally indicate that the social returns to education are positive large and competitive with returns to investment in physical capital that such estimates are good guides for public resource allocation has however been questioned the heart of the problem lies in the interpretation of the positive relationship between the education and the earnings of workers whether as the conventional estimates assume the coefficient of the education variable in the earnings function measures the effect on the productivity of workers of human capital acquired in school it has been hypothesized that education in part or instead represents screening for native ability and motivation or credentialism and that as a consequence conventional measures of the social benefit of education are substantially upward biased 2 in this paper we attempt to distinguish the influence on earnings of cognitive achievement native ability and years of education as a means of adjudicating the human capital screening and credentialist hypotheses our econometric analysis is based on two rigorously comparable micro data sets from kenya and tanzania generated by surveys of the urban wage labor force specifically for this study these data sets contain the usual variables found in earnings function estimates of the benefits of schooling individual earnings years of education and years of employment experience in addition they contain two variables measures of the worker s cognitive skills and of his or her reasoning ability not previously found in studies of developing countries and only rarely found in studies of the education earnings relationship in developed countries 3 with these variables we can estimate the direct effects on earnings of cognitive skills ability and years of schooling by using them to estimate educational production functions and educational attainment functions and linking these functions with the earnings function in a recursive framework we can also assess the various indirect effects on earnings of ability and years of schooling having data sets from two countries very similar with respect to size resource endowments structure of production and employment and level of development means that not only can we subject our results to the usual statistical tests but we can also assess their replicability both kenya and tanzania have nearly achieved the objective of universal primary education while university enrollments remain at less than 1 percent of the relevant age group the important policy issues re boissiere development research department the world bank 1818 h street washington d c 20433 knight institute of economics and statistics oxford university sabot williams college williamstown ma 01267 we are grateful to the educational testing service of princeton for the design of tests used in this study and to j armitage j behrman j hausman d hendry d jamison and an anonymous referee for their insights and advice helpful comments were also received from participants in seminars at oxford and yale universities the views presented here are our own they should not be interpreted as reflecting those of the world bank george psacharopoulos 1973 1981 contains a listing of 44 countries in which rate of return studies had been conducted and of the estimates obtained 2for instance kenneth arrow 1973 mark blaug 1976 samuel bowles and herbert gintis 1976 john riley 1979 michael spence 1976 and lester thurow 1975 3for attempts to control for ability and or for cognitive achievement in studies for the united states see jere behrman et al 1980 gary chamberlain and zvi griliches 1977 griliches and william mason 1972 michael olneck 1977 paul taubman and terence wales 1974 taubman 1975 and david wise 1975 see also the survey articles by griliches 1977 1979 in most instances the data refer to special subgroups in the population and clear distinction cannot be made between natural ability and cognitive skills acquired in school

more possessions more worry abstract a common wisdom asserts that the wider the universe of assets to choose from the greater the investor s welfare we show that this is not the case in practice where parameters have to be estimated even when the estimates are unbiased surprisingly risk aversion plays a crucial role corresponding to the desirability of asset expansion by dividing investors in three groups investors with very low risk tolerance and investors with very high risk tolerance are better off with asset expansion and investors with moderate risk tolerance are worse off despite the option to refrain from investing in the additional asset

hiv testing subjective beliefs and economic behavior this paper examines the effects of learning hiv status on economic behavior among rural malawians according to economic life cycle models if learning hiv results is informative about additional years of life being diagnosed hiv positive or negative should predict changes in consumption investment and savings behavior with important micro and macro economic implications using an experiment that randomly assigned incentives to learn hiv results i find that while learning hiv results had short term effects on subjective belief of hiv infection these differences did not persist after two years consistent with this there were relatively few differences two years later in savings income expenditures and employment between those who learned and did not learn their status

the long run economic costs of aids primarily a disease of young adults aids imposes economic costs that could be devastatingly high in the long run by undermining the transmission of human capital the main driver of long run economic growth across generations aids makes it harder for victims children to obtain an education and deprives them of the love nurturing and life skills that parents provide these children will in turn find it difficult to educate their children and so on an overlapping generations model is used to show that an otherwise growing economy could decline to a low level subsistence equilibrium if hit with an aids type increase in premature adult mortality calibrating the model for south africa where the hiv prevalence rate is over 20 percent simulations reveal that the economy could shrink to half its current size in about four generations in the absence of intervention programs to combat the disease and to support needy families could avert such a collapse but they imply a fiscal burden of about 4 percent o