do minority white unemployment differences really exist we develop a model of labor force status federal employment nonfederal employment unemployment and out of the labor force that depends on human capital variables local labor market conditions and personal characteristics according to the estimated model for white non hispanic males and females a substantial difference exists between blacks and white non hispanics even after correction for the control variables however the control variables explain almost all of the difference between hispanics and white non hispanics

estimating the lead time demand distribution when the daily demand is non normal and autocorrelated hon shiang lau abstract this paper develops convenient formulas for estimating the probability distribution of lead time demand when the inventory item s daily demand follows a probability distribution of any arbitrary shape and when simple univariate models can be found for the autocorrelated daily demand series numerical examples are presented to illustrate the use of these formulas the numerical results also indicate that significant error may be incurred when inventory decisions are made without proper consideration of the autocorrelations or the arbitrary distribution shapes of daily demands

learning and control in a changing economic environment abstract in this paper we investigate optimal bayesian learning and control with lagged dependent variables and time varying unknown parameters we assess both the performance of alternative decision rules as in the computationally oriented dual control literature as well as the dynamics of learning and convergence of beliefs as in the more theoretically oriented bayesian learning literature our numerical results indicate that the optimal decision rule involves a noticeable degree of experimentation for moderate to large levels of uncertainty in most situations though the optimal rule will remain less activist than a certainty equivalent rule and induce gradualism exceptions occur when the process to be controlled is near the deterministic steady state in this situation we find that the decision maker will repeatedly undertake costly experiments the extent of optimal experimentation is lower if the unknown parameter is perceived to vary over time in contrast to the fixed parameter case however parameter uncertainty is continually renewed and the incentive to experiment never ceases

how much demand should be fulfilled we study the inventory replenishment of a product whose demand can be manipulated by restricting the supply this research is motivated by a novel marketing tactic employed by manufacturers of fashion and luxury items such a tactic combines innovative marketing with deliberate understocking in an attempt to create shortages i e waitlists that add to the allure and sense of exclusivity of a product and stimulate its demand we model the problem as a finite horizon periodic review system where demand in each period is a decreasing function of the net ending inventory in the previous period although the optimal structure can be complex in general under certain conditions we are able to characterize the optimal policy as a state dependent monotone base stock policy we compare this policy with the optimal policy for the case in which demand is independent of the net inventory we also show that understocking is optimal in various scenarios we then propose a novel strategy called the inventory withholding strategy to further explore the wait list effect by making customers wait even when there is inventory on hand to satisfy them our numerical experiments study the impact of various model parameters in combination with the wait list effect on the optimal policy and the corresponding expected profits

federal and union job queues further evidence from the us labour market recent research on union differentials suggests that although the premium to unionization is higher in the private sector it can hardly be ignored in the federal sector consequently the nature and length of the federal queue may differ between union and non union sectors similarly the union queue may not necessarily be homogeneous between federal and private sectors we estimate separate queues for federal union federal non union and private union jobs from the same sample this avoids the problem of simultaneity between the federal queue and the union queue in addition it explores several important differences that exist between these queues

optimal policies and approximations for a serial multiechelon inventory system with time correlated demand since clark and scarf s pioneering work most advances in multiechelon inventory systems have been based on demand processes that are time independent this paper revisits the serial multiechelon inventory system of clark and scarf and develops three key results first we provide a simple lower bound approximation to the optimal echelon inventory levels and an upper bound to the total system cost for the basic model of clark and scarf second we show that the structure of the optimal stocking policy of clark and scarf holds under time correlated demand processes using a martingale model of forecast evolution third we extend the approximation to the time correlated demand process and study in particular for an autoregressive demand model the impact of lead times and autocorrelation on the performance of the serial inventory system

the role of energy in real business cycle models abstract this paper modifies hansen s 1985 analysis of a real business cycle mode with indivisible labor by explicitly including energy as a productive input and modelling the relative price of energy as an exogenous random process one goal is to determine the extent to which the introduction of energy price shocks reduces the reliance of the real business cycle model on unobserved technology shocks the other goal following christiano and eichenbaum 1991 is to compare the correlation between real wages and hours predicted by the energy inclusive model to that predicted by hansen s model

a robustness study of a multi echelon inventory model via simulation abstract this paper examines the robustness of a standard model of multi echelon inventory systems specifically the models discussed in axsater oper res 48 5 2000 686 a simulation model was developed to explore the model s ability to predict system performance for a two echelon one warehouse multiple retailer system using r q inventory policies under conditions that violate the model s fundamental modeling assumptions in particular the impact of non stationary demand on this stationary demand inventory model was examined the model performs well at the low demand and large retailer order batch size situations but our testing of the model indicated that care must be taken when applying this model to situations that violate its fundamental assumption these results should help practitioners to better understand the assumptions of these models and to determine when or when not to apply these models in practice

job queues and the union status of workers this paper develops a model of the determination of the union status of workers that allows for the possibility of queuing for union jobs the empirical results derived using a sample from the university of michigan panel study of income dynamics are supportive of the queuing hypothesis the no queue model can be rejected using a likelihood ratio test this suggests that a simple probit or logit model for union status is misspecified because it is not based on any consistent behavioral theory an important implication of the model is that because most new entrants to the labor market prefer union jobs but cannot get them and because accrual of nonunion seniority makes workers progressively less likely to desire union jobs the union status of workers is largely determined by their success in being selected from the queue early in their working life

a bayesian approach to optimal monetary policy with parameter and model uncertainty abstract this paper undertakes a bayesian analysis of optimal monetary policy for the u k we estimate a suite of monetary policy models that include both forward and backward looking representations as well as large and small scale models we find an optimal simple taylor type rule that accounts for both model and parameter uncertainty for the most part backward looking models are highly fault tolerant with respect to policies optimized for forward looking representations while forward looking models have low fault tolerance with respect to policies optimized for backward looking representations in addition backward looking models often have lower posterior probabilities than forward looking models bayesian policies therefore have characteristics suitable for inflation and output stabilization in forward looking models

oil and the macroeconomy since world war ii all but one of the u s recessions since world war ii have been preceded typically with a lag of around three fourths of a year by a dramatic increase in the price of crude petroleum this does not mean that oil shocks caused these recessions evidence is presented however that even over the period 1948 72 this correlation is statistically significant and nonspurious supporting the proposition that oil shocks were a contributing factor in at least some of the u s recessions prior to 1972 by extension energy price increases may account for much of post opec macroeconomic performance

a periodic review model with serially correlated inventory level dependent demand abstract it has been established that the demand rates of many consumer products are serially correlated and are dependent on the amount of inventory displayed to the customer a periodic review model is developed that considers both of these effects an adaptive base stock policy based on the critical fractile is presented and a solution methodology is developed the effect of this demand pattern on the safety stock requirement is investigated

impact of the worker s employment probability on wage rates the employment probability is a significant determinant of the worker s wage rate expecially in the presence of employers hiring discrimination several tests suggest that the omission of this variable in the wage regression may lead to misspecification

a neoclassical model of unemployment and the business cycle this paper investigates a general equilibrium model of unemployment and the business cycle in which specialization of labor plays a key role a rational expectations equilibrium with fully flexible wages and prices can exhibit unemployment in which the marginal product of employed workers exceeds the reservation wage of those who are without jobs workers are unemployed either because they are in the process of relocating for a better job or because they are waiting for conditions in the depressed sector to improve moreover seemingly small disruptions in the supplies of primary commodities such as energy could be the source of fluctuations in aggregate employment and can exert surprisingly large effects on real output

black white life cycle earnings differences and the vintage hypothesis a longitudinal analysis a common finding of virtually all previous studies of black white earnings differences is that the earnings of white males appear to rise at a more rapid rate with each additional year of work experience or with age than do the earnings of black workers this finding has been noted by economists since at least the mid 1950 s when morton zeman called

this is what happened to the oil price macroeconomy relationship abstract many of the quarterly oil price increases observed since 1985 are corrections to even bigger oil price decreases the previous quarter when one looks at the net increase in oil prices over the year recent data are consistent with the historical correlation between oil shocks and recessions

safety stock determination with correlated demands and arbitrary lead times abstract in this new paper a new method is proposed for determining the safety stock when daily demands are autocorrelated and lead times follow an arbitrary distribution the method is then used as a basis for examining effects on the safety stock when the usual assumptions namely independence and normality of daily demand and normality of lead times are violated the new method is derived by using inequalities on the basis of probability arguments it is simple to use and provides an upper bound of the safety stock further numerical investigation based on the new method shows that the effect of autocorrelation is more pronounced than departure from normality in determining the safety stock substantial error may be incurred if such autocorrelation is ignored in the test cases

coordinating lead times and safety stocks under autocorrelated demand we consider a supply chain in which orders and lead times are linked endogenously as opposed to assuming lead times are exogenous this assumption is relevant when a retailer s orders are produced by a supplier with finite capacity and replenished when the order is completed the retailer faces demands that are correlated over time either positively or negatively which may for example be induced by a pricing or promotion policy the auto correlation in demand affects the order stream placed by the retailer onto the supplier and this in turn influences the resulting lead times seen by the retailer since these lead times also determine the retailer s orders and its safety stocks which the retailer must set to cover lead time demand there is a mutual dependency between orders and lead times the inclusion of endogenous lead times and autocorrelated demand represents a better fit with real life situations however it poses some additional methodological issues compared to assuming exogenous lead times or stationary demand processes that are independent over time by means of a markov chain analysis and matrix analytic methods we develop a procedure to determine the distribution of lead times and inventories that takes into account the correlation between orders and lead times our analysis shows that negative autocorrelation in demand although more erratic improves both lead time and inventory performance relative to iid demand positive correlation makes matters worse than iid demand due to the endogeneity of lead times these effects are much more pronounced and substantial error may be incurred if this endogeneity is ignored

oil shocks and aggregate macroeconomic behavior the role of monetary policy hamilton and herrera hh have provided an interesting comment on our 1997 paper bernanke gertler and watson 1997 bgw we take the opportunity offered to us by the editors to respond briefly the goal of bgw was to show that the magnitude and shape of the economy s response to a particular exogenous shock will typically depend critically on how monetary policy makers choose to react to the shock as a consequence we argued that assessments of the importance of monetary policy for real activity should take into account the systematic portion of policy i e the policy rule as well as the unsystematic component i e monetary policy shocks the specific type of exogenous shock that we considered in bgw was a sharp increase in the price of oil of the magnitude observed during several episodes in the 1970s using a modified var framework we considered counterfactual scenarios in which monetary policy represented by the level of the federal funds rate does not respond to an oil price shock we found that the adverse effects of an oil price shock on output are reduced considerably when the endogenous response of the funds rate is shut off indeed our point estimates suggested that the endogenous response of monetary policy accounted for virtually all the negative impact of the oil shock on this research was funded in part by nsf grants to each of the authors we thank michele cavallo for research assistance

benefits from u s monetary policy experimentation in the days of samuelson and solow and lucas a policy maker knows two models of ination unemplo yment dynamics one implies an exploitable trade o the other does not the policy maker s prior probability over the two models is part of his state vector bayes law converts the prior probability into a posterior probability at each date and gives the policy maker an incentive to experiment for two models calibrated to u s data through the early 1960s we isolate the component of government policy that is due to experimentation by comparing the outcomes from two bellman equations the rst of which experiments and learns the second of which learns but doesn t experiment we interpret the second as an anticipated utility model and study how well its outcomes approximate those from the experiment and learn bellman equation the approximation is good for our calibrations the benets from purposeful experimentation are small

an alternative approach to the analysis of wage differentials a key question in many studies of male female or black white wage differentials is how much of the differential can be explained by economic factors and how much remains unexplained the unexplained portion is then ascribed to discrimination since oaxaca 17 first formalized this decomposition the residual difference methodology has been the dominant methodology utilized in empirical studies of wage differentials 4 7 8 10 15 18 but recently the validity of the assumptions underlying the residual difference methodology have been called into question by butler 5 6 in this paper the theoretical underpinnings of the residual difference methodology are reexamined and an alternative theoretical framework for this methodology is suggested the new framework overcomes the shortcomings inherent in oaxaca s specification of the model and therefore provides a sound theoretical foundation for the residual difference decomposition

robust optimal policy in a forward looking model with parameter and shock uncertainty this paper characterizes a robust optimal policy rule in a simple forward looking model when the policymaker faces uncertainty about model parameters and shock processes we show that the robust optimal policy rule is likely to involve a stronger response of the interest rate to fluctuations in inflation and the output gap than is the case in the absence of uncertainty thus parameter uncertainty alone does not necessarily justify a small response of monetary policy to perturbations however uncertainty may amplify the degree of super inertia required by optimal monetary policy we finally discuss the sensitivity of the results to alternative assumptions copyright 2007 john wiley sons ltd

sex differentials in unemployment rates a case for no concern this paper reevaluates the concept of unemployment in the context of differing labor market and nonmarket opportunities for men and women discussing common fallacies in female to male unemployment rate comparisons and their use as an indicator of labor market equality suggestive empirical evidence is presented for an alternative unemployment rate concept for women for interpreting the procyclical variation in female to male unemployment rate differentials and for decomposing unemployment differences into differences in labor market characteristics and in behavioral coefficients for the two sexes the paper concludes that a large part of the observed unemployment rate differential may be attributed to the definition and methodology used in deriving unemployment statistics rather than to discrimination in productive opportunities

effects of correlation on intermittent demand forecasting and stock control abstract this study investigates the effects of three different types of correlation on forecasting and stock control of intermittent demand items applying appropriate forecasting and stock control methods to theoretically generated compound poisson demand data we show that correlation in intermittent demand does play a role in forecast quality and stock control performance negative autocorrelation levels lead to higher service levels than positive values while cost does not significantly change our results also show that high intermittency levels intensify these changes in service level we also show that cross correlation produces results in the opposite direction of autocorrelation in size or intervals that is positive negative cross correlation leads to higher lower service levels

learning by doing and the value of optimal experimentation abstract recent research on learning by doing has provided the limit properties of beliefs and actions for a class of learning problems in which experimentation is an important aspect of optimal decision making however under these conditions the optimal policy cannot be derived analytically because bayesian learning about unknown parameters introduces a nonlinearity in the dynamic optimization problem this paper utilizes numerical methods to characterize the optimal policy function for a learning by doing problem that is general enough for practical economic applications the optimal policy is found to incorporate a substantial degree of experimentation under a wide range of initial beliefs about the unknown parameters dynamic simulations indicate that optimal experimentation dramatically improves the speed of learning and the stream of future payoffs furthermore these simulations reveal that a policy which separates control and estimation and does not incorporate experimentation frequently induces a long lasting bias in the control and target variables while these sequences tend to converge steadily under the optimal policy they frequently exhibit non stationary behavior when estimation and control are treated separately

the role of model uncertainty and learning in the u s postwar policy response to oil prices abstract this paper studies optimal monetary policy in a framework that explicitly accounts for policymakers uncertainty about the channels of transmission of oil prices into the economy more specifically using postwar us data i examine the evolution of the policy recommendations originating from an optimal linear regulator problem that encompasses model uncertainty and learning as proposed by cogley and sargent 2005b in this environment i find that one of the underlying models dominates the robust interest rate response to oil prices and i show that this result is due to the instability of this specification in the sample period under analysis