dynamic programming model estimates of social security disability insurance application timing this paper develops a dynamic programming model of the social security disability insurance ssdi application timing decision we estimate the time to application from the point at which a health condition first begins to affect the kind or amount of work that a currently employed person can do we use health and retirement study hrs and restricted access social security earnings data for estimation our results show that the type of work limiting health condition presence of employer accommodation and the relative value of income in the application state to income in the work state significantly affect the timing of ssdi application copyright 2004 john wiley sons ltd

choice under uncertainty a model of applications for the social security disability insurance program abstract not all people with health problems are disabled some individuals with severe physical or mental impairments such as blindness or limb amputation continue to hold jobs and generally function satisfactorily they constitute however a group of potentially disabled individuals who might apply and qualify for disability insurance or other disability related benifits if they were to lose their jobs or to decide that employment offered an inadequate financial or non pecuniary reward thus disability or a health related inability to work is more than a medical problem but involves motivational and attitudinal factors we specify a model of the application process which we model as choice under uncertainty about approval of an application for disability insurance we specify the possible outcomes to the choice process of an individual in which the probability of acceptance for disability insurance is a key consideration we then estimate a joint model of labor supply and application to the disability insurance program based on the 1972 survey we then compare our results to the observed time series applications process since 1976 lastly we estimate the sensitivity of the application process to the probability of acceptance and the level of benifits

bubbles and volatility of stock prices effect of mimetic contagion the author discusses the effect of the mimetic contagion on the dynamics of stock prices each investor bids and or asks prices such that adjusts to his present value calculated from his incomplete information set and to the average price of others buyers and sellers mimetic contagion an original stochastic treatment based on the equation of motion of the probability density function is used to calculate the equations of the mean and variance of the market price as soon as the agents are mimetic and or have correlated present values then the moments of the market price are driven away from the fundamental ones copyright 1991 by royal economic society

the econometrics of kinked budget constraints in the last several years a branch of applied econometrics has developed which is devoted to the development of techniques for the estimation of demand and other functions when the budget constraint is piecewise linear or kinky that is when the constraint consists of a number of segments joined together at kink points such constraints most frequently arise from government tax and transfer programs for example the federal income tax imposes a piecewise linear schedule by the use of constant marginal tax rates within brackets a problem analyzed by hausman 1981 the payroll tax in the social security system likewise generates a kinked schedule inasmuch as the marginal tax rate on earnings is zero above a certain earnings maximum federal and state transfer programs for the poor result in piecewise linear constraints because transfer benefits are taxed in the sense of a negative income tax as income rises and because that tax rate falls to zero at the kink point where an individual or family loses eligibility for the benefit altogether many government transfer programs impose additional nonlinearities by altering this tax rate by discrete amounts over the range of positive benefits as well but kinked constraints sometimes arise in nongovernment contexts a well known example being the block pricing schedule commonly set by utilities and volume discounting in general kinked budget constraints create two difficulties that have several interesting facets one difficulty is that changes in tax and transfer schedules can have unexpected effects that can be exactly the opposite in sign to those expected from economic theory examples of this phenomenon are given below the second difficulty that with which this paper is mostly concerned relates to the implications of kinked budget

a damped diffusion framework for financial modeling and closed form maximum likelihood estimation abstract asset price bubbles can arise unintentionally when one uses continuous time diffusion processes to model financial quantities we propose a flexible damped diffusion framework that is able to break many types of bubbles and preserve the martingale pricing approach damping can be done on either the diffusion or drift function oftentimes certain solutions to the valuation pde can be ruled out by requiring the solution to be a limit of martingale prices for damped diffusion models monte carlo study shows that with finite time series length maximum likelihood estimation often fails to detect the damped diffusion function while fabricates nonlinear drift function an alternative method based on ait sahalia s specification test on parametric models is proposed

on rational bubbles and fat tails this paper addresses the statistical properties of time series driven by rational bubbles a la blanchard and watson 1982 using insights on the behavior of multiplicative stochastic processes we demonstrate that the tails of the unconditional distribution emerging from such bubble processes follow power laws exhibit hyperbolic decline more precisely we find that rational bubbles predict a fat power tail for both the bubble component and price differences with an exponent smaller than 1 the distribution of returns is dominated by the same power law over an extended range of large returns although power law tails are a pervasive feature of empirical data these numerical predictions are in disagreement with the usual empirical estimates it therefore appears that exogenous rational bubbles are hardly reconcilable with some of the stylized facts of financial data at a very elementary level

momentum investment strategies portfolio performance and herding a study of mutual fund behavior this study analyzes the extent to which mutual funds purchase stocks based on their past returns as well as their tendency to exhibit herding behavior i e buying and selling the same stocks at the same time the authors find that 77 percent of the mutual funds were momentum investors buying stocks that were past winners however most did not systematically sell past losers on average funds that invested on momentum realized significantly better performance than other funds the authors also find relatively weak evidence that funds tended to buy and sell the same stocks at the same time copyright 1995 by american economic association

social security disability insurance applications awards and lifetime income flows this article provides new evidence about the impact of social security disability insurance on male labor force participation decisions based on estimates from a structural model of applications awards and state contingent lifetime income flows the lifetime framework makes it possible to consider long term opportunity costs associated with early labor force withdrawal and the disincentive to applications resulting from the statutory waiting period before benefits may be received estimation techniques account for the self selected nature of the pool of applicants when predicting the individual specific probability of acceptance and the opportunity costs of applying

the decline in male labor force participation comment in an article in thisjournal parsons 1980a analyzes the doubling in the rate of nonparticipation in the labor force of older men since 1946 using cross sectional data from the national longitudinal survey parnes et al 1970 in an index function model of the labor force participation decision he tests the assertion that the withdrawal of older males is attributable to the rapid expansion of alternatives to work provided by the social security disability insurance ssdi program he reports an elasticity of nonparticipation with respect to the replacement rate of ssdi benefits of 631 and concludes that the recent decline in labor force participation can be largely explained by the increased generosity of social welfare transfers particularly social security disability payments p 130 the magnitude of parsons s estimate and its impact on the public debate over disability transfer policy require careful scrutiny of its basis in section i we describe parsons s econometric model and construction of variables in section ii we provide a critique in section iii we test the robustness of parsons s elasticity estimate by presenting alternative estimates based on corrections and extensions of his basic model section iv concludes

stock market crashes as social phase transitions abstract stock market crashes are traumatic events that affect the lives of millions of people around the globe and have tremendous economic implications crashes are not only dramatic but often completely unexpected the 1987 crash for example was not induced by any obvious trigger even after the fact it is hard to find the reason for the crash why did the market crash in october rather than in september or december why did it crash at all to this day we lack satisfactory answers this paper shows that spontaneous market crashes can be explained by a social phase transition mechanism similar to statistical mechanics phase transitions investors heterogeneity plays the role of temperature and is key in determining the possibility and magnitude of the crash the analysis suggests that dramatic crashes are a robust and inevitable property of financial markets it also implies that market crashes should be preceded by an increase in price volatility as empirically observed thus market crashes like earthquakes are a fundamental and unavoidable part of our world however we can develop early warning systems that may help minimize the damage

disability transfers and the work decision of older men the potential causal relationship between the availability and generosity of disability transfers and the nonparticipation rates of older men is often asserted and much studied parsons 1980 haveman and wolfe 1984 leonard 1986 however estimates of the magnitude of this linkage vary widely the growth in transfer availability and generosity has been credited with from 30 to 100 percent of the significant post 1960 fall in older male participation rates the disparity in these research results stems primarily from 1 alternative sources of data that differentially constrain estimation of relevant expected wage and transfer incomes 2 specifications that are unable to distinguish income transfer from labor market effects and 3 reliance on measures of health status that are endogenous to the work leisure decision this study seeks to narrow the range of estimates by addressing each of these issues our utility maximization model of work status choice assumes that workers who differ in health status choose between the mutually exclusive options of working at the wage offered for their characteristics and accepting public or private disability transfers because the income flows in the two options are censored they are estimated using switching regression techniques as expectations conditional on exogenous individual characteristics hence accounting for the potentially endogenous process that separates wage earners from transfer recipients the marginal utilities of income from the two sources are allowed to differ because of stigma effects in the estimation we adjust the choice based nature of our sample employ longitudinal earnings data to measure expected changes in as distinct from the expected level of income in the two options and use a separately estimated latent health status measure largely purged of its endogeneity with the participation decision

the rise in the disability rolls and the decline in unemployment between 1984 and 2001 the share of nonelderly adults receiving social security disability insurance income di rose by 60 percent to 5 3 million beneficiaries rapid program growth despite improving aggregate health appears to be explained by reduced screening stringency declining demand for less skilled workers and an unforeseen increase in the earnings replacement rate we estimate that the sum of these forces doubled the labor force exit propensity of displaced high school dropouts after 1984 lowering measured u s unemployment by one half a percentage point steady state calculations augur a further 40 percent increase in the rate of di receipt

the danger of assuming homogeneous expectations the capital asset pricing model the black scholes option valuation model and many other economic models rely on the assumption of homogeneous expectations what are the effects of heterogeneous expectations on price determination are the homogeneous expectations models approximately correct we compare stock price dynamics in models with homogeneous and heterogeneous expectations heterogeneous expectations appear to play a crucial role in risky asset price determination when homogeneous expectations are assumed unacceptable market inefficiencies are observed the introduction of even a small degree of diversity of expectations changes the dynamics dramatically and the result is a much more realistic market these findings make one wonder how far the equilibrium prices of the capm and black scholes model are from the true values in markets with heterogeneous expectations

social interaction and stock market participation we propose that stock market participation is influenced by social interaction in our model any given social investor finds the market more attractive when more of his peers participate we test this theory using data from the health and retirement study and find that social households those who interact with their neighbors or attend church are substantially more likely to invest in the market than non social households controlling for wealth race education and risk tolerance moreover consistent with a peer effects story the impact of sociability is stronger in states where stock market participation rates are higher

portfolio optimization when asset returns have the gaussian mixture distribution abstract in this paper we consider a portfolio optimization problem where the underlying asset returns are distributed as a mixture of two multivariate gaussians these two gaussians may be associated with distressed and tranquil market regimes in this context the sharpe ratio needs to be replaced by other non linear objective functions which in the case of many underlying assets lead to optimization problems which cannot be easily solved with standard techniques we obtain a geometric characterization of efficient portfolios which reduces the complexity of the portfolio optimization problem

the retirement health nexus a new measure of an old puzzle traditional empirical models of retirement which use a self assessed health measure have often found that the wage rate has a surprisingly small effect on retirement using both a self reported health measure and one not based on self report subsequent mortality experience in a more general reduced form joint demand framework we test the importance of the interaction effects of health and retirement our findings are consistent with a joint determination of health and retirement the wage elasticity using either health measure is about equal to that found in a single equation model when a mortality measure is used but all three elasticities are five times greater than one found using self reported health in a traditional single equation model

the economic implications of public disability insurance in the united states a review of previous analyses of labor supply effects of social security disability insurance di concludes that estimates of labor supply effects and net social costs are upward biased because they ignore interactions between di and other insurances a model of optimal insurance postinjury accommodations and labor supply shows that reduction in labor supply and increase in consumption when disabled do not necessarily imply moral hazard optimal postinjury accommodations vary inversely with firm size the americans with disabilities act will reduce wages and labor supply of healthy workers particularly in small firms effects on labor supply of the disabled are ambiguous

the health and earnings of rejected disability insurance applicants applicants for social security disability benefits who fail to pass the medical screening form a natural control group for beneficiaries data drawn from the 1972 and 1978 surveys of the disabled done for the social security administration show that fewer than 50 percent of rejected male applicants work typical earnings of those that do are less than 59 percent of median earnings for other men their age these data cast doubt on recent econometric work that suggests that the disincentive effects of the social security disability program have been substantial copyright 1989 by american economic association

discrete choice with social interactions this paper provides an analysis of aggregate behavioural outcomes when individual utility exhibits social interaction effects we study generalized logistic models of individual choice which incorporate terms reflecting the desire of individuals to conform to the behaviour of others in an environment of noncooperative decisionmaking laws of large numbers are generated in such environments multiplicity of equilibria in these models which are equivalent to the existence of multiple self consistent means for average choice behaviour will exist when the social interactions exceed a particular threshold local stability of these multiple equilibria is also studied the properties of the noncooperative economy are contrasted with the properties of an economy in which a social planner determines the set of individual choices finally a likelihood function based on the theoretical model is given and conditions for the econometric identifiability of the model are established

disability earnings income and consumption using longitudinal data for the period 1968 2005 for a sample of male household heads we determine the prevalence of disability during the working years and examine how the extent of disability affects a range of outcomes including earnings income and consumption we have seven main findings first disability rates are high we divide the disabled along two dimensions based on the persistence and severity of their work limiting condition we estimate that a person reaching age 56 has a 53 percent chance of having been disabled at least once during his working years and a 19 percent chance that he has begun a chronic and severe disability second the economic consequences of disability are frequently profound ten years after disability onset a person with a chronic and severe disability on average experiences a 68 percent decline in earnings a 32 percent decline in after tax income a 22 percent decline in food and housing consumption and a 21 percent decline in food consumption third the various economic consequences differ sharply across disability groups the outcome declines for those with a chronic and severe disability are often more than twice as large as those for the average disabled fourth our findings show the partial and incomplete roles that individual savings family support and social insurance play in reducing the consumption drop that follows disability only about half of this most disabled group reports receiving social security disability insurance or supplemental security income fifth we find a noticeable fall in earnings and income prior to the onset of a reported disability consumption also falls somewhat suggesting that future disability is partially but incompletely predictable in the short run sixth time use and detailed consumption data further indicate that disability is associated with a decline in well being seventh the quantities we have estimated combined with elasticities from the literature allow us to examine the optimality of current compensation for the disabled we find that the current compensation for our most disabled group appears to be lower than is optimal

is mean variance analysis applicable to hedge funds abstract this paper shows that the mean variance analysis of hedge funds approximately preserves the ranking of preferences in standard utility functions this extends the results of levy and markowitz 1979 levy h markowitz h m 1979 approximating expected utility by a function of mean and variance american economic review 69 308 317 and hlawitschka 1994 hlawitschka w 1994 the empirical nature of taylor series approximations to expected utility american economic review 84 713 719 for individual stocks and portfolios of stocks

disability insurance rejection rates and the labor supply of older workers abstract we investigate the effects of trying to mitigate moral hazard in the disability insurance di program by raising the stringency of the screening process for applicants we do so by studying a dramatic increase in rejection rates for the di program in the late 1970s which varied substantially across the us states we find that each 10 rise in denial rates led to a statistically significant 2 8 fall in labor force non participation among 45 64 year old males we also find that the denial rate increases effectively targeted their incentive effects to more able individuals according to an anthropometric measure of disability

a life cycle model of unemployment and disability insurance abstract a general equilibrium life cycle model is developed in which individuals choose a sequence of saving and labor supply faced with search frictions and uncertainty in longevity health status and medical expenditures unemployed individuals decide whether to apply for disability insurance di benefits if eligible we investigate the effects of cash transfer and in kind medicare component of the di system on the life cycle employment without medicare benefits di coverage could fall significantly we also study how di interacts with reforms of social security and medicare and find that di enrollment amplifies the effects of reforms

does disability insurance receipt discourage work using examiner assignment to estimate causal effects of ssdi receipt abstract we present the first causal estimates of the effect of social security disability insurance benefit receipt on labor supply using all program applicants we use administrative data to matc

participation and investment decisions in a retirement plan the influence of colleagues choices abstract this paper investigates whether peer effects play an important role in retirement savings decisions we use individual data from employees of a large university to study whether individual decisions to enroll in a tax deferred account plan sponsored by the university and the choice of the mutual fund vendor for people who choose to enroll are affected by the decisions of other employees in the same department to overcome the identification problems we divide the departments into sub groups along gender status age and tenure lines and we instrument the average participation of each peer group by the salary or tenure structure in this group our results suggest that peer effects may be an important determinant of savings decisions

how do unemployment insurance benefits affect the decision to apply for social security disability insurance this paper examines whether unemployment insurance ui benefits affect the decision to apply for social security disability insurance di using data from the survey of income and benefits matched to administrative records on di applications i find that higher ui benefits reduce applications for di this substitution effect is imprecisely estimated but economically significant implying that a 1 00 increase in ui benefits reduces di expenditures by 15 cents recognizing this cost saving effect would increase the optimal ui benefit level by more than 20 percent for coefficients of relative risk aversion ranging from two to five

the welfare implications of increasing disability insurance benefit generosity abstract in order to evaluate whether workers are over or under insured through the disability insurance di program we develop a framework that allows us to simulate the benefits as well as the costs associated with marginal changes in payment generosity from a representative cross sectional sample of the population under the assumption that individuals are reasonably risk averse we find that the typical worker would value increased benefits somewhat above the average costs of providing them however whether the benefit increases tend to lower or raise utility when we average across all individuals in our sample is sensitive to assumptions that affect the relative marginal utility of income to disabled individuals

the economic implications of disability insurance in canada the article empirically estimates the effects of disability pensions provided under the canada quebec pension plans on the labor force participation rates of males aged 45 64 years two data sets are used one consists of pooled cross section annual time series data by province for the years 1975 83 the other consists of observations as of 1985 on 651 males in the specified age group naive estimation results from both sets of data suggest a large negative effect of pension income in the case of the micro data this effect becomes small and statistically nonsignificant when more sophisticated estimation methods are used

aching to retire the rise in the full retirement age and its impact on the social security disability rolls abstract the social security amendments of 1983 reduced the generosity of social security retired worker benefits in the u s by increasing the program s full retirement age from 65 to 67 and increasing the penalty for claiming benefits at the early retirement age of 62 these changes were phased in gradually so that individuals born in or before 1937 were unaffected and those born in 1960 or later were fully affected no corresponding changes were made to the program s disabled worker benefits and thus the relative generosity of social security disability insurance ssdi benefits increased in this paper we investigate the effect of the amendments on ssdi enrollment by exploiting variation across birth cohorts in the policy induced reduction in the present value of retired worker benefits our findings indicate that the amendments significantly increased ssdi enrollment since 1983 with an additional 0 6 of men and 0 9 of women between the ages of 45 and 64 receiving ssdi benefits in 2005 as a result of the changes our results further indicate that these effects will continue to increase during the next two decades as those fully exposed to the reduction in retirement benefit generosity reach their fifties and early sixties

diversification as a public good community effects in portfolio choice within a rational general equilibrium model in which agents care only about personal consumption we consider a setting in which due to borrowing constraints individuals endowed with local resources underparticipate in financial markets as a result investors compete for local resources through their portfolio choices even with complete financial markets and no aggregate risk agents may herd into risky portfolios this yields a pareto dominated outcome as agents introduce community risk unrelated to fundamentals moreover if some agents are behaviorally biased or cannot completely diversify their holdings rational agents may choose more extreme portfolios and amplify the effect

disability benefit generosity and labor force withdrawal abstract a key component for estimating the optimal size and structure of disability insurance di programs is the elasticity of di claiming with respect to benefit generosity yet in many countries including the united states all workers face identical benefit schedules which are a function of one s labor market history making it difficult to separate the effect of the benefit level from the effect of unobserved preferences for work on individuals claiming decisions to circumvent this problem we exploit exogenous variation in di benefits in austria arising from several reforms to its di and old age pension system in the 1990s and 2000s we use comprehensive administrative social security records data on the universe of austrian workers to compute benefit levels under six different regimes allowing us to identify and precisely estimate the elasticity of di claiming with respect to benefit generosity we find that over this time period a 1 increase in potential di benefits was associated with a 1 2 increase in di claiming

herding among security analysts the paper shows that the buy or sell recommendations of security analysts have a signi cant positive in uence on the recommendations of the next two analysts this in uence can be traced to short lived information in the most recent revisions in contrast the in uence of the prevailing consensus is not stronger if the consensus accurately forecasts subsequent stock price movements this indicates consensus herding consistent with models in which analysts herd based on little information the consensus also has a stronger in uence when market conditions are favorable the resulting poorer information aggregation could cause bull markets to be intrinsically more fragilea e g bikhchandani et al j political economy 100 5 1992 992 1026 2000 elsevier science s a all rights reserved jel classixcation g11 g14 g24

does the choice of performance measure influence the evaluation of hedge funds abstract the sharpe ratio is adequate for evaluating investment funds when the returns of those funds are normally distributed and the investor intends to place all his risky assets into just one investment fund hedge fund returns differ significantly from a normal distribution for this reason other performance measures for hedge fund returns have been proposed in both the academic and practice oriented literature in conducting an empirical study based on return data of 2763 hedge funds we compare the sharpe ratio with 12 other performance measures despite significant deviations of hedge fund returns from a normal distribution our comparison of the sharpe ratio to the other performance measures results in virtually identical rank ordering across hedge funds

a microscopic model of the stock market cycles booms and crashes abstract we present a model of the stock market based on the behavior of individual investors simulations exhibit rich phenomena which include cycles booms and crashes low dividend yield and more homogeneous market participants are shown to induce crashes

the impact of economic conditions on participation in disability programs evidence from the coal boom and bust abstract we examine the impact of the coal boom of the 1970 s and the coal bust of the 1980 s on disability program participation these shocks provide clear evidence that as the value of labor market participation increases disability program participation falls for the disability insurance program the elasticity of payments with respect to local earnings is between 0 3 and 0 4 and for supplemental security income the elasticity is between 0 4 and 0 7 consistent with a model where qualifying for disability programs is costly the relationship between economic conditions and program participation is much stronger for permanent than for transitory economic shocks

market efficiency of oil spot and futures a mean variance and stochastic dominance approach this paper examines the market efficiency of oil spot and futures prices by using both mean variance mv and stochastic dominance sd approaches based on the west texas intermediate crude oil data for the sample period 1989 2008 we find no evidence of any mv and sd relationships between oil spot and futures indices this infers that there is no arbitrage opportunity between these two markets spot and futures do not dominate one another investors are indifferent to investing spot or futures and the spot and futures oil markets are efficient and rational the empirical findings are robust to each sub period before and after the crises for different crises and also to portfolio diversification

market liquidity hedging and crashes in the absence of significant news hedging strategies were blamed for the stock market crash of october 1987 but traditional models cannot explain how a relatively small amount of selling could cause so large a price drop the authors develop a rational expectations model in which prices play an important role in shaping expectations markets are much less liquid in their model than in traditional models discontinuities or crashes can occur even with relatively little hedging the model is consistent with theories as disparate as keynes beauty contest insights and thom s catastrophe analysis and suggests means to reduce volatility copyright 1990 by american economic association

financial crises and interacting heterogeneous agents in this paper we examine various types of financial crises and conjecture their underlying mechanisms using a deterministic heterogeneous agent model ham in a market maker framework forward looking investors update their price expectations according to psychological trading windows and cluster themselves strategically to optimize their expected profits the switches between trading strategies lead to price dynamics in market that subsequently move price up and down and in the extreme case cause financial crises the model suggests that both fundamentalists and chartists could potentially contribute to the financial crises