industrial actions in schools strikes and student achievement many jurisdictions ban teacher strikes on the assumption that they negatively affect student achievement but there is surprisingly little research on this question the majority of existing studies make cross section comparisons of the achievement of students who do or do not experience a strike they conclude that strikes do not have an impact i present new estimates of this impact of strikes using an empirical strategy that controls for fixed student characteristics at the school cohort level and a sample of industrial actions by teachers in the province of ontario the results indicate that teacher strikes in grades 5 or 6 have a negative statistically significant impact on test score growth between grade 3 and grade 6 the largest impact is on math scores 29 of the standard deviation of test scores across school grade cohorts greves dans les ecoles greves et resultats scolaires plusieurs juridictions prohibent les greves de professeurs a partir du postulat qu elles affectent negativement les resultats des etudiants mais il y a et c est surprenant peu de recherches sur cette question la plupart des etudes qui existent font des comparaisons transversales des resultats des etudiants qui ont et n ont pas subi de greves on conclut que ces greves n ont pas d impact l auteur presente de nouvelles evaluations de cet impact des greves a partir d une strategie empirique qui normalise pour certaines caracteristiques fixes des etudiants au niveau de la cohorte et qui porte sur un echantillon de greves par des professeurs dans la province de l ontario les resultats montrent que les greves de professeurs en 4e et 5e annee ont un impact statistiquement significatif sur la progression dans les tests standardises entre la 3e et la 6e annee l impact le plus important est en mathematique de l ordre de 29 dans l ecart type des resultats des tests pour les cohortes d ecole niveaux

an inventory model for deteriorating items with stock dependent consumption rate and shortages under inflation and time discounting this paper derives an inventory model for deteriorating items with stock dependent consumption rate and shortages under inflation and time discounting over a finite planning horizon we show that the total cost function is convex with the convexity a simple solution algorithm is presented to determine the optimal order quantity and the optimal interval of the total cost function the results are discussed with a numerical example and particular cases of the model are discussed in brief a sensitivity analysis of the optimal solution with respect to the parameters of the system is carried out

partial backlogging inventory lot size models for deteriorating items with fluctuating demand under inflation abstract in this paper the traditional inventory lot size model is extended to allow not only for general partial backlogging rate but also for inflation the assumptions of equal cycle length and constant shortage length imposed in the model developed by moon et al moon i giri b c ko b 2005 economic order quantity models for ameliorating deteriorating items under inflation and time discounting european journal of operational research 162 3 773 785 are also relaxed for any given number of replenishment cycles the existence of a unique optimal replenishment schedule is proved and further the convexity of the total cost function of the inventory system in the number of replenishments is established the theoretical results here amend those in yang et al yang h l teng j t chern m s 2001 deterministic inventory lot size models under inflation with shortages and deterioration for fluctuating demand naval research logistics 48 2 144 158 and provide the solution to those two counterexamples by skouri and papachristos skouri k papachristos s 2002 note on deterministic inventory lot size models under inflation with shortages and deterioration for fluctuating demand by yang et al naval research logistics 49 5 527 529 finally we propose an algorithm to find the solution and obtain some managerial results by using sensitivity analyses

how teachers unions affect education production this study helps to explain why measured school inputs appear to have little effect on student outcomes particularly for cohorts educated since 1960 teachers unionization can explain how public schools simultaneously can have more generous inputs and worse student performance using panel data on united states school districts i identify the effect of teachers unionization through differences in the timing of collective bargaining especially timing determined by the passage of state laws that facilitate teachers unionization i find that teachers unions increase school inputs but reduce productivity sufficiently to have a negative overall effect on student performance union effects are magnified where schools have market power

estimating the effects of global patent protection in pharmaceuticals a case study of quinolones in india under the trips agreement wto members are required to enforce product patents for pharmaceuticals the debate about the merits of this requirement has been extremely contentious many low income economies claim that patent protection for pharmaceuticals will result in substantially higher prices for medicines with adverse consequences for the health and well being of their citizens on the other hand research based global pharmaceutical companies argue that prices are unlikely to rise significantly because most patented products have therapeutic substitutes in this paper we empirically investigate the basis of these claims central to the ongoing debate is the structure of demand for pharmaceuticals in poor economies where because health insurance coverage is so rare almost all medical expense are met out of pocket using a detailed product level data set from india we estimate key price and expenditure elasticities and supply side parameters for the fluoroquinolones sub segment of the systemic anti bacterials i e antibiotics segment of the indian pharmaceuticals market we then use these estimates to carry out counterfactual simulations of what prices profits and consumer welfare would have been had the fluoroquinolone molecules we study been under patent in india as they were in the u s at the time our results suggest that concerns about the potential adverse welfare effects of trips may have some basis we estimate that in the absence of any price regulation or compulsory licensing the total annual welfare losses to the indian economy from the withdrawal of the four domestic product groups in the fluoroquinolone sub segment would be on the order of u s 450 million or about 73 of the sales of the entire systemic anti bacterials segment in 2000 of this amount foregone profits of domestic producers constitute roughly 50 million or 11 the overwhelming portion of the total welfare loss therefore derives from the loss of consumer welfare in contrast the profit gains to foreign producers in the absence of any price regulation are estimated to be only around 53 million per year

joint inventory allocation and pricing decisions for perishable products abstract we jointly determine the price and the inventory allocation for a perishable product with a predetermined lifetime we assume that the price of the product increases as the time when it perishes approaches as in the airline industry demand for the product is price sensitive to maximize the expected revenue we developed a discrete time dynamic programming model to obtain the optimal prices and the optimal inventory allocations for the product with a two period lifetime we then proposed three heuristics when the lifetime is longer than two periods the computational results showed that the expected revenues from the proposed heuristics were very close to that of the optimal solution we extended these results to i the case where the price for the product consistently decreases and ii the case where the price for the product first increases and later decreases

fuzzy inventory problems for perishable commodities abstract this paper considers an inventory control model for a single perishable product with a fuzzy shortage cost and a fuzzy outdating cost this model is a single period horizon model due to fuzziness of shortage and outdating costs an expected profit function is represented with a fuzzy set the purpose of this paper is to find the solution maximizing the expected profit function after defining a nondominated ordering quantity based on fuzzy max order we seek some of them and investigate an effect of the fuzziness on the obtained solutions

blood platelet inventory management with protection levels abstract we consider a discrete time inventory system for a perishable product where demand exists for product of different ages an example of such a product is blood platelets in addition to the classical costs for inventory holding outdating and shortage our model includes substitution mismatch costs incurred when a demand for a certain aged item is satisfied by a different aged item we propose a simple inventory replenishment and allocation heuristic to minimize the expected total cost over an infinite time horizon in our heuristic inventory of the newest items is replenished in fixed quantities and the newest items are protected for future use by limiting some substitutions when making allocation decisions according to a critical level policy we model our problem as a markov decision process mdp derive the costs of our heuristic policy and computationally compare this policy to extant near optimal policies in the literature our extensive computational study shows that our policy leads to superior performance compared to existing heuristics in the literature particularly when supplies are limited

review of inventory systems with deterioration since 2001 abstract this paper presents an up to date review of the advances made in the field of inventory control of perishable items deteriorating inventory the last extensive review on this topic dates back to 2001 goyal s k and giri b c recent trends in modeling of deteriorating inventory european journal of operational research 134 1 16 since then over two hundred articles on this subject have been published in the major journals on inventory control indicating the need for a new review we use the classification of goyal and giri based on shelf life characteristics and demand characteristics contributions are highlighted by discussing main system characteristics including price discounts backordering or lost sales single or multiple items one or two warehouses single or multi echelon average cost or discounted cash flow and payment delay

the effect of teachers unions on education production evidence from union election certifications in three midwestern states using a unique data set on teachers union election certifications from iowa indiana and minnesota i estimate the effect of teachers unions on school district resources and on student educational attainment my empirical strategy allows for nonparametric leads and lags of union age i find no impact on teacher pay or per student district expenditures but that unions increase teacher employment by 5 i find no class size effect because of enrollment increases in unionized districts and i estimate that unions have no net effect on high school dropout rates these findings highlight the importance of correctly measuring unionization status

a production inventory model for a deteriorating item with trended demand and shortages abstract a production inventory model is developed for a deteriorating item over a finite planning horizon with a linear time varying demand finite production rate and shortages the resulting nonlinear constrained minimization problem is numerically solved by using the box complex algorithm the optimal number of production cycles that minimizes the average system cost is determined sensitivity analysis of the optimal solution is carried out

trade in environmental goods evidences from an analysis using elasticities of trade costs negotiations on the liberalization of environmental goods egs and services within the wto doha round mandated in november 2001 are facing specific challenges conflicting interests and differing perceptions of the benefits of increased trade in egs were reflected in different approaches proposed for determining egs using import data of 34 organisation for economic co operation and development oecd member countries and from a sample of 167 countries from 1995 to 2012 we discuss the trade effect of reducing barriers on egs we analyze the lists of egs proposed by the asia pacific economic cooperation and oecd using a translog gravity model we found that removing tariff barriers for egs will have a modest impact because for the biggest importers and exporters elasticities of trade costs are very low while for most trading relationships they are very high making it difficult for exporters to maintain their markets overall our results suggest that because of their substantial effect on international trade future negotiations on egs should also address the issues of standards and nontariff barriers

determining optimal selling price and lot size with a varying rate of deterioration and exponential partial backlogging in this paper a deterministic inventory model for deteriorating items with price dependent demand is developed the demand and deterioration rates are continuous and differentiable function of price and time respectively in addition we allow for shortages and the unsatisfied demand is partially backlogged at a negative exponential rate with the waiting time under these assumptions for any given selling price we first develop the criterion for the optimal solution for the replenishment schedule and prove that the optimal replenishment policy not only exists but also is unique if the criterion is not satisfied the inventory system should not be operated next we show that the total profit per unit time is a concave function of price when the replenishment schedule is given we then provide a simple algorithm to find the optimal selling price and replenishment schedule for the proposed model finally we use numerical examples to illustrate the algorithm

should retailers hold a perishable product having different ages the case of a homogeneous market and multiplicative demand model this paper specializes in investigating the common practice of the coexistence of multiple competing perishables each with different age and price all of which are associated with the same product the fundamental postulate investigated by our model is the replacement of the policy of selling a single product age with a policy of selling multiple product ages coexistence of multiple product ages on the shelf is associated with shorter cycle lengths as well as with providing consumers with the option of choosing between a fresher product on average and a cheaper product on average we use a utility corresponding to the factors of price and time we axiomatically assume the coexistence of multiple product ages while posing several propositions which present certain difficulties in preferring this policy with the support of a multiplicative demand with respect to price and time and by assuming that consumers are homogeneous in their preferences we analyze a deterministic version of the problem and derive the optimal pricing policy given any cycle length and any duration for which both types coexist on the shelf we prove that the optimal policy is not to sell multiple product types at all by means of a numerical example we show that the operational mode of the coexistence of multiple product ages reduces the retailer s profit per unit time by at least 15 sensitivity analysis of some of the most influential parameters is introduced the superiority of the single product age operational mode over the competitor mode sharply decreases as the optimal cycle length is approached

perishable inventory management with stochastic leadtime and different selling prices abstract this paper discusses a model for a perishable product with stochastic procurement leadtime and different selling prices this model is a generalization of the one period horizon model of nahmias 4 5 ishii et al 3 and nose et al 7 for the model the optimal ordering policy and its properties are derived

pass through of exchange rates and competition between floaters and fixers this paper studies how a rise in the share of u s imports from china or any country with a fixed exchange rate could disproportionately lower pass through of exchange rates to u s import prices we develop a theoretical model showing how changes in the competitive environment induce exporters from other countries to lower markups in response to a dollar depreciation thereby moderating pass through the model indicates that a particular local bias condition is necessary for this effect and that free entry amplifies it the model also produces an approximately log linear structural equation for pass through regressions including the china share panel regressions over 1993 2006 indicate that the rising share of trade from china or from all countries with fixed exchange rates can explain a decline in pass through by about onefifth of its size

perishable inventory management subject to stochastic leadtime abstract this paper discusses the model for a perishable product with the stochastic procurement leadtime zero or 1 unit leadtime is considered and its optimal ordering policy is derived this is a generalization of the one period horizon model of nahmias 4 further the chance constraint as for shortage is added and under this additional constraint again optimal ordering policy is obtained

an optimal production inventory model for deteriorating items with multiple market demand the global markets of today offer more selling opportunities to the deteriorating items manufacturers but also pose new challenges in production and inventory planning from a production management standpoint opportunities to exploit the difference in the timing of the selling season between geographically dispersed markets for deteriorating items are important to improving a firm s profitability in this paper we examined the above issue with an insightful production inventory model of a deteriorating items manufacturer selling goods to multiple markets with different selling seasons we also provided a solution procedure to find the optimal replenishment schedule for raw materials and the optimal production plan for finished products a numerical example was then used to illustrate the model and the solution procedure finally sensitivity analysis of the optimal solution with respect to major parameters was carried out

new products with a symmetric aids expenditure function abstract we study a symmetric aids expenditure function that allows for variation in the range of goods solving for the reservation prices for goods not available a convenient form for the expenditure function is obtained this functional form should prove useful in monopolistic competition models were the range of products changes due to entry and exit

perishable inventory control with two types of customers and different selling prices under the warehouse capacity constraint abstract this paper discusses an inventory model for a single perishable product with two types of customers high priority and low priority ones the former buys only the newest commodity while the latter buys either one whether the newest or not different selling prices reflecting the remaining lifetime of commodity and the constraint of the warehouse capacity i e the capacity of own warehouse and so the excess inventory are stored in the rental warehouse further demands in successive periods are assumed to be independent nonnegative random variables with known distribution functions and high priority and low priority demands are independent stock is depleted by high priority demand first and then low priority demand using fifo issuing policy assuming two types of shortage costs different selling prices outdating cost purchasing cost two types of holding costs an optimal ordering policy to maximize the expected profit is derived

can school sports reduce racial gaps in truancy and achievement while existing research supports that participation in high school athletics is associated with better education and labor market outcomes the mechanisms through which these benefits accrue are not well established using individual microdata collected daily and team specific schedules we retrieve estimates of the causal effect of high school athletic participation on absenteeism suggesting that participation decreases absences driven primarily by reductions in unexcused absences in boys there are also strong game day effects in truancy in both boys and girls with truancy declines on game days more than offset by subsequent absenteeism important heterogeneity by race gender and family structure may serve to substantially reduce racial gaps in truancy and achievement jel i21 l83

a perishable inventory model with markovian renewal demands abstract in the inventory model people usually assume that the inter demand time is independently identical distributed which may not be true in reality here we study an s s continuous review model for items with an exponential random lifetime and a general markovian renewal demand process by constructing markovian renewal equations we derive the mean and the variance of the reorder cycle time and lead to a simple expression for the total expected long run cost rate the numerical results illustrate the system behavior and lead to managerial insights into controlling such inventory systems

on a finite horizon production lot size inventory model for deteriorating items an optimal solution abstract a generalized production lot size inventory model for deteriorating items over a finite planning horizon is considered the demand production and deteriorating rates are assumed to be known and continuous functions of time shortages are allowed and completely backlogged the conditions under which the system total cost attains its unique global minimum are derived an example which illustrate the applicability of theoretical results is also introduced

an optimal replenishment policy for deteriorating items with effective investment in preservation technology abstract in this paper considering the amount invested in preservation technology and the replenishment schedule as decision variables we formulate an inventory model with a time varying rate of deterioration and partial backlogging the objective is to find the optimal replenishment and preservation technology investment strategies while maximizing the total profit per unit time for any given preservation technology cost we first prove that the optimal replenishment schedule not only exists but is unique next under given replenishment schedule we show that the total profit per unit time is a concave function of preservation technology cost we then provide a simple algorithm to figure out the optimal preservation technology cost and replenishment schedule for the proposed model we use numerical examples to illustrate the model

two warehouse inventory models for deteriorating items with shortages under inflation abstract in this paper the two warehouse inventory problem for deteriorating items with constant demand rate and shortages under inflation is considered in contrast to the traditional deterministic two warehouse inventory model with shortages at the end of each replenishment cycle an alternative model in which each cycle begins with shortages and ends without shortages is proposed here the optimal solution not only exists but also is unique comparing these two two warehouse inventory models the study shows that the proposed model is less expensive to operate than the traditional one in the case of the inflation rate is greater than zero hence under the consideration of inflationary effect the proposed model is less expensive finally some numerical examples for illustration are provided

an economic order quantity model for deteriorating items with partially permissible delay in payments linked to order quantity abstract to attract more sales suppliers frequently offer a permissible delay in payments if the retailer orders more than or equal to a predetermined quantity w in this paper we generalize goyal s k 1985 eoq under conditions of permissible delay in payments journal of the operational research society 36 335 338 economic order quantity eoq model with permissible delay in payment to reflect the following real world situations 1 the retailer s selling price per unit is significantly higher than unit purchase price 2 the interest rate charged by a bank is not necessarily higher than the retailer s investment return rate 3 many items such as fruits and vegetables deteriorate continuously and 4 the supplier may offer a partial permissible delay in payments even if the order quantity is less than w we then establish the proper mathematical model and derive several theoretical results to determine the optimal solution under various situations and use two approaches to solve this complex inventory problem finally a numerical example is given to illustrate the theoretical results