network externalities technological progress and the competition of market contracts abstract network externalities are used to describe the fact that many modern products become more valuable the more users adopt products of the same technology where network externalities and technological progress exist the various kinds of inefficiencies discussed in the recent literature can be explained by different types of contracts the main categories analysed are simple market contracts update contracts and service contracts it is shown that these types of contract emerge endogenously from the incentive structure of profit maximizing firms competition between these contracts may substantially reduce inefficient allocations caused by network externalities

an extended production recycling model with stationary demand and return rates abstract a production recycling system is investigated a constant demand can be satisfied with production and recycling the used items are bought back and then recycled the non recycled products are disposed of two types of models will be analyzed the first model examines the eoq related costs and minimizes the relevant costs the second model generalizes the first model with the introduction of the cost function with linear waste disposal recycling production and buyback costs it is asked whether the pure either production or recycling or mixed strategies are optimal and it will be shown that under these circumstances the mixed strategies are dominated by the pure strategies the paper generalizes a former model proposed by the authors for the case of one recycling and one production batch to the case of arbitrary batch numbers

integrating replenishment decisions with advance demand information there is a growing consensus that a portfolio of customers with different demand lead times can lead to higher more regular revenues and better capacity utilization customers with positive demand lead times place orders in advance of their needs resulting inadvance demand information this gives rise to the problem of finding effective inventory control policies under advance demand information we show that state dependent s s and base stock policies are optimal for stochastic inventory systems with and without fixed costs the state of the system reflects our knowledge of advance demand information we also determine conditions under which advance demand information has no operational value a numerical study allows us to obtain additional insights and to evaluate strategies to induce advance demand information

inventories stock outs and production smoothing if stock outs are ignored and if demand shocks are additive then optimal behaviour requires that the marginal cost of production mc be equated with the expected marginal revenue of increasing expected sales by one unit emr however with more general demand shocks and still ignoring stock outs the excess of mc over emr has the same sign as the covariance of the slope of the demand curve and the marginal valuation of inventory the equality of emr and mc is also broken by taking account of stock outs even if demand shocks are additive if there is a production lag then taking account of stock outs implies that optimal behaviour will be characterized by production smoothing even if the cost of production is linear two alternative definitions of production smoothing are presented and optimal behaviour in the presence of stock outs displays each type of smoothing it is a well known proposition that a firm producing a storable good under conditions of increasing marginal cost will tend to smooth the time profile of its production relative to the time profile of its sales the incentive to smooth production arises from the fact that the cost function is a convex function of the level of production for a given average level of production average costs can be reduced by reducing the variation in production of course if the cost function is linear in the level of production then this incentive to smooth production disappears however we will demonstrate in this paper that if the possibility of stock outs is explicitly incorporated into the firm s dynamic optimization problem i e if we impose a non negativity constraint on inventories and if there is a lag in production then optimal behaviour can be characterized by production smoothing even if the cost function is linear

bounded growth of the bullwhip effect under a class of nonlinear ordering policies abstract this paper analyzes the bullwhip effect in multi echelon supply chains under a general class of nonlinear ordering policies a describing function approach from control theory is used to derive closed form formulas to predict amplification of order fluctuations along the supply chain it is proven that with consideration of nonlinearity in the ordering policy the magnitude of the bullwhip effect will eventually become bounded after growing through the first few stages of the supply chain it is also proven that the average customer demand as well as the demand fluctuation frequency would directly affect the bounded magnitude while the suppliers demand forecasting method has no effect at all for illustration analytical results for a class of order up to policies are derived and verified by numerical simulations the proposed modeling framework holds the promise to not only explain empirical observations but also serve as the basis for developing counteracting strategies against the bullwhip effect

technological expectations and adoption of improved technology abstract attention is focused upon the adoption demand rather than the creation supply of new technology which improves from time to time based on the expected flow of technological progress over which the firm demander has no control it must decide either to adopt the current best available technology or to postpone adoption the distinguishing features of the model are that more than one technological innovation is anticipated and expectations about the likelihood of such innovations are revised as time passes since the last innovation our analysis shows that the firm will adopt the current best practice if its technological lag exceeds a certain threshold moreover as time passes without new technological advances it may become profitable to purchase a technology that has been available even though it was not profitable to do so in the past

markups aggregation and inventory adjustment in this paper i suggest a unified explanation for two puzzles in the inventory literature first estimates of inventory speeds of adjustment in aggregate data are very small relative to the apparent rapid reaction of stocks to unanticipated variations in sales second estimates of inventory speeds of adjustment in firm level data are significantly higher than in aggregate data the paper develops a multisector model where inventories are held to avoid stockouts and price markups vary along the business cycle the omission of countercyclical markup variations from inventory targets introduces a downward bias in estimates of adjustment speeds obtained from partial adjustment models when the cyclicality of markups differs across sectors this downward bias is shown to be more severe with aggregate rather than firm level data similar results apply not only to inventories but also to labor and prices montercarlo simulations of a calibrated version of the model suggest that these biases are quantitatively significant

customer order information leadtimes and inventories we have an inventory to manage the scenario is standard in all respects save one instead of arriving unannounced customers provide advance warning of their demands how should we use this information and what is its effect on system performance the answers turn out to be strikingly simple there are very simple policies which perform effectively in some cases optimally also such demand leadtimes improve performance in precisely the same way that replenishment leadtimes degrade it

money and the business cycle with one period nominal contracts a modified version of the nominal contract developed by j a gray 1976 and s fischer 1977 is introduced in a general equilibrium model with money which has been used in the real business cycle literature money is introduced in the model through cash in advance constraint two kinds of contracts are examined namely a nominal wage contract and a nominal price contract the nominal wage contract improves the fit of the model in many respects the nominal price contract increases the output volatility enormously but it has some unrealistic features

uncertainty in sales and inventory behaviour in the u s trade sectors this paper investigates uncertainty in sales and inventory behavior for the u s wholesale and retail trade sectors first using a vector error correction model with garch m the authors find that the uncertainty measured by forecast error variance in sales does not affect inventory behavior in both trade sectors second using forecast error variance decomposition and estimated permanent components they observe that the uncertainty may be attributed more to demand shocks than to cost shocks

the stabilizing effect of inventory in supply chains this paper presents a hierarchical model framework for the analysis of the stabilizing effect of inventories in multiechelon manufacturing distribution supply chains this framework is used to compare the variance of demand to the variance of replenishment orders at different echelons of the system e g retailer wholesaler empirical data and experience with management games suggest that in most industries inventory management policies can have a destabilizing effect by increasing the volatility of demand as it passes up through the chain the bullwhip effect our model helps to explain these observations and indicates mechanisms that can promote stabilization the analysis results also define sufficient conditions for the existence of stabilization and relate these conditions to the optimality of myopic control policies

production smoothing in the linear quadratic inventory model contrary to popular belief the linear quadratic inventory model does not imply that in response to demand shocks output is always less variable than sales when demand shocks are not anticipated and without this assumption it is hard to see why firms should hold inventories in the first place it is shown that output can be more variable than sales even when the only shocks are demand shocks and the inventory target is not a rising function of sales the variance of output will typically exceed that of sales when the firm s marginal cost curve is fairly flat copyright 1994 by royal economic society

the linear quadratic inventory model as a micro foundation for keynesian theories of the business cycle abstract aggregate inventory investment is invariably procyclical this suggests that inventories play a destabilizing role in the economy as predicted by early keynesian models of the business cycle however this behavior is believed to be inconsistent with the most prominent micro theory of inventories the linear quadratic model this is not the case the linear quadratic model when placed in a simple macro framework can account for the procyclical behavior of inventory investment even when the only shocks are independent demand shocks inventory targets are independent of sales and individual firms adjust inventories slowly towards their target levels

the effect of information sharing on supply chain stability and the bullwhip effect this paper analyzes the bullwhip effect in multi stage supply chains operated with linear and time invariant inventory management policies and shared supply chain information such information includes past order sequences and inventory records at all supplier stages the paper characterizes the stream of orders placed at any stage of the chain when the customer demand process is known and ergodic and gives an exact formula for the variance of the orders placed the paper also derives robust analytical conditions based only on inventory management policies to predict the presence of the bullwhip effect and bound its magnitude these results hold independently of the customer demand the general framework proposed in this paper allows for any inventory replenishment policies any ways of sharing and utilizing information and any customer demand processes it is also shown as a special case that sharing customer demand information across the chain significantly reduces but does not completely eliminate the bullwhip effect

the production and inventory behavior of the american automobile industry understanding inventory movements is central to an understanding of business cycles this paper presents an empirical study of the behavior of inventories in the automobile industry it finds that inventory behavior is well explained by the assumption of intertemporal optimization with rational expectations the underlying cost structure appears to have substantial costs of changing production as well as substantial costs of being away from target inventory thelatter being a function of current sales given this cost structure whether inventory behavior is stabilizing or destabilizing depends on the characteristics of the demand process in the automobile industry inventory behavior is destabilizing the variance of production is larger than the variance of sales

a measure of bullwhip effect in supply chains with a mixed autoregressive moving average demand process abstract in this paper we quantify the impact of the bullwhip effect the phenomenon in which information on demand is distorted as moving up a supply chain for a simple two stage supply chain with one supplier and one retailer assuming that the retailer employs a base stock inventory policy and that the demand forecast is performed via a mixed autoregressive moving average model arma 1 1 we investigate the effects of the autoregressive coefficient the moving average parameter and the lead time on the bullwhip effect

information distortion in a supply chain the bullwhip effect this article originally appeared in management science april 1997 volume 43 number 4 pp 546 558 published by the institute of management sciences consider a series of companies in a supply chain each of whom orders from its immediate upstream member in this setting inbound orders from a downstream member serve as a valuable informational input to upstream production and inventory decisions this paper claims that the information transferred in the form of orders tends to be distorted and can misguide upstream members in their inventory and production decisions in particular the variance of orders may be larger than that of sales and distortion tends to increase as one moves upstream a phenomenon termed bullwhip effect this paper analyzes four sources of the bullwhip effect demand signal processing rationing game order batching and price variations actions that can be taken to mitigate the detrimental impact of this distortion are also discussed

measuring endogenous supply chain volatility beyond the bullwhip effect most recent research on supply chain volatility has focused on one particular dimension of that volatility namely the amplification of upstream order variability while not ignoring this aspect of supply chain volatility we focus on a different but equally critical aspect of volatility the cyclical oscillation of on hand and on order inventories about their target values we prove that such cyclicality does not require oscillatory or random retailer demand as a prerequisite the resulting volatility is therefore endogenous rather than simply an amplification of exogenous demand inputs we also measure the amount of amplification resulting from a step increase in demand the order amplification is the product of two factors each of which is clearly linked to either on hand or on order inventory our results attest that supply chain volatility can arise in the absence of exogenous oscillatory or random demand and suggest strategies for avoiding or minimizing such volatility

an examination of consumer heterogeneity in a stochastic model of consumer purchase dynamics with explanatory variables abstract a stochastic model of brand choice and purchase incidence is proposed that relates marketing variables including advertising exposures to brand performance measures such as market share penetration and depth of repeat purchase dynamics over time the approach considers various aspects of consumer heterogeneity including individual differences in brand loyalty levels advertising exposures and purchase rates for a population of consumers a major focus of this study is on the evaluation of the impact of consumer heterogeneity in alternative models on the basis of single source scanner panel data for an actual market situation in particular we demonstrate the critical importance of considering heterogeneity over a consumer population as a means of enhancing descriptive and predictive model fit as well as for allowing the analysis of advertising media schedules

nonconvex costs and the behavior of inventories this paper explores one possible explanation for the apparent excess volatility of production relative to sales nonconvexities in the technology facing firms it is shown that if firms operate in a region of declining marginal costs then small shifts in demand can cause production to jump substantially estimates for six production to stock industries as well as the automobile industry suggest that all these industries behave as if they were operating in the region of nonconvex costs the results have important implications not only for inventory investment but also for the cyclical behavior of productivity and prices

the bullwhip effect in supply chain networks this paper analyzes the propagation and amplification of order fluctuations i e the bullwhip effect in supply chain networks operated with linear and time invariant inventory management policies the supply chain network is allowed to include multiple customers e g markets any network structure with or without sharing information the paper characterizes the stream of orders placed by any supplier for any stationary customer demand processes and gives exact formulas for the variance of the orders placed and the amplification of order fluctuations the paper also derives robust analytical conditions based only on inventory management policies to predict the presence of the bullwhip effect for any network structure any inventory replenishment policies and arbitrary customer demand processes numerical examples show that the analytical results accurately quantify the bullwhip effect managerial insights are drawn from the analysis the methodology presented in this paper generalizes those in previous studies for serial supply chains

modeling and analysis of cash flow bullwhip in supply chain abstract the bullwhip effect that occurs in supply chain inventory can distort demand forecasts and lead to inefficiencies such as excessive inventory stock outs and backorders in this paper we theorize that inventory bullwhip also leads to cash flow bullwhip cfb specifically this paper focuses on studying cfb by developing mathematical and simulation models to analyze the relationship between inventory and cash flow bullwhip by using cash conversion cycle ccc as a metric the mathematical models for inventory bullwhip are developed for two stage and generic multi stage supply chains and then by extending these inventory models the cfb models are developed for two stage cfb predicted by the proposed mathematical models approximately differ 14 from detailed simulation models we find that increasing variability increases inventory and cash flow bullwhip along with lead time whereas increasing the demand observation period has the opposite effect the average marginal impact of the bullwhip effect on the cfb is approximately 20 additionally the cfb is also an increasing function of an expected value of inventory and a decreasing function of an expected value of demand

a diffusion model incorporating product benefits price income and information we start by assuming that a major benefit of many new durable products such as dishwashers and microwave ovens is time savings others such as vcrs also enhance the value of our leisure time using a household production framework we demonstrate that a utility maximizing individual will have a reservation price for the product which is a function of the product benefits and his wage rate by assuming that the wage rate has an extreme value distribution across the population we are able to derive for the aggregate process an income price dependent logistic adoption equation we then allow for the possibility that certain eligible consumers may delay their purchase of the product because they are unaware that it exists are suspicious of its quality or expect its price to fall unawareness uncertainty and hope for further price declines are assumed to decrease with the increase in the number of previous adopters the resulting diffusion model has the property that the product life cycle phenomenon can be explained jointly or separately by the income price process and the awareness uncertainty expectations process using data on household income on durable penetration within different income classes and on first purchase sales the aggregate diffusion model and its premises are tested and supported it is found that both the income price and awareness uncertainty expectations processes are at work however the dependence of the awareness uncertainty expectations delay process on the number of previous adopters e g word of mouth type effect exists only in certain product categories and is usually relatively weak it is demonstrated that if the word of mouth type effects are weak a price skimming strategy is optimal for a monopolist and also is likely to be implemented by oligopolists the sales forecasting implications of the model also are pursued

the production impact of cash for clunkers implications for stabilization policy during july and august of 2009 americans purchased nearly 700 000 new automobiles or light trucks under the government s cash for clunkers program officially the car allowance rebate system or cars under the terms of the purchase qualified buyers traded in their old vehicles to receive a rebate on the price of a new vehicle the amount of the rebate either 3 500 or 4 500 depended on both the model that was traded in and the model that was acquired the direct cost to taxpayers of subsidizing these purchases was roughly 2 8 billion the program had two primary goals to reduce energy consumption and pollution by inducing consumers to replace their old gas guzzlers with newer fuel efficient models and to serve as a stimulus for the troubled automobile industry and the u s economy as a whole in this article we take a close look at the second objective exploring how the cars program affected sales and more important production in the automobile industry 1 drawing on our findings we then propose an answer to the more difficult question of the program s impact on u s gross domestic product gdp 2 in line with other recent studies our analysis shows that the cars program had only a transitory cumulative effect on sales we estimate an initial impact of about 450 000 additional automobile sales but these were essentially shifted from the periods before and especially after the program we calculate that by january 2010 the cumulative effect of the cars program on auto sales was essentially zero 3 more important for our purposes however is the program s effect on automobile production while most studies of cars have focused on sales we argue that the program s success as a stimulus to the economy hinges on its impact on production production increases are more likely to translate into higher gdp and employment gdp being fundamentally a measure of production sales clearly rose at the outset but given that the industry can simply let inventory stocks absorb the increase in sales higher sales alone do not imply higher gdp or employment 4 overall we find that the program had a very modest and short lived effect on production production was about 200 000 units higher during the program in comparison to the 450 000 increase in sales sales from september 2009 to january 2010 were correspondingly lower than they would have been in the absence of cars which allowed producers to have lower production while still replenishing their inventory stocks thus on a quarterly basis we estimate that the cars program shifted production by around 100 000 units from 2009q4 and 2010q1 to 2009q3 these calculations suggest that the program had a negligible direct effect on gdp shifting less than roughly 2 billion or less than one tenth of 1 of gdp into 2009q3 from the subsequent two quarters this contrasts starkly with a study released by the department of transportation dot in the immediate aftermath of the program which concluded that cars had given a substantial boost to both gdp and employment in the final section of the article we discuss why our conclusions differ from those of the dot study our findings raise broader questions beyond just this particular program about the efficacy of efforts to stimulate short term spending it is clearly a mistake to gauge their impact by just looking at the spending they induce without looking at the supply side it is reasonable to expect that producers will use other margins than production and employment to respond to temporary movements in sales so the only question is quantitative how large is the gap between the sales and production impact we find it to be large in the case of cash for clunkers in what follows we will lay out the economics behind our analysis by examining how rebates and other transitory price changes affect consumer purchases and manufacturers inventory decisions

price competition and co operation in a duopoly closed loop supply chain abstract this paper studies co operation and competition issues in a closed loop supply chain the supply chain comprises of two manufacturers who compete for selling their new product as well as for collection of the used products for remanufacturing through a common retailer to analyze the situation mathematical models are developed here for three different cases i non co operative system ii channel co operative system and iii global co operative system for each of the cases we have characterized optimal wholesale price and fraction of collection of used product to draw more managerial insights we also examine the sensitivity of various parameters such as market size acquisition cost and transfer price on total channel profit a numerical study is carried out to illustrate the model and the results reveal that global co operative system is the best among all the three cases considered here weighted shapely value mechanism is used for sharing of surplus generated in the system due to channel co operation

analysis of the bullwhip effect in two parallel supply chains with interacting price sensitive demands abstract this paper offers insights into how the bullwhip effect in two parallel supply chains with interacting price sensitive demands is affected in contrast to the situation of a single product in a serial supply chain in particular this research studies two parallel supply chains each consisting of a manufacturer and a retailer and the external demand for a single product depends on its price and the other s price in a situation in which each price follows a first order autoregressive process in this paper we propose an analytical framework that incorporates two parallel supply chains and we explore their interactions to determine the bullwhip effect we identify the conditions under which the bullwhip effect is amplified or lessened with interacting price sensitive demands relative to the situation without interaction

technology adoption in the presence of network externalities we analyze technology adoption in industries where network externalities are significant the pattern of adoption depends on whether technologies are sponsored a sponsor is an entity that has property rights to the technology and hence is willing to make investments to promote it key findings include the following 1 compatibility tends to be undersupplied by the market but excessive standardization can occur 2 in the absence of sponsors the technology superior today has a strategic advantage and is likely to dominate the market 3 when one of two rival technologies is sponsored that technology has a strategic advantage and may be adopted even if it is inferior 4 when two competing technologies both are sponsored the technology that will be superior tomorrow has a strategic advantage

inventories and sticky prices note in a recent contribution to this review alan blinder provides an interesting analysis of the relationship between optimal inventory decisions and the process of price adjustment arguing that inventory permits separation of production and sale decisions and allows the firm greater flexibility in responding to anticipated demand disturbances blinder shows that the responsiveness of relative prices depends critically upon the cost of storage and the temporal structure of the demand shocks few economists would fault the intuitive substance of blinder s basic proposition and the proposition is justified with characteristic precision the analysis however is considerably less general than blinder maintains the formal argument of his paper relies upon a simple model of a monopolist capable of backlogging orders and storing unsold goods as the model is constructed order backlogs assume a role of fundamental importance in any stationary equilibrium this feature of the model vitiates blinder s extension of his result to situations in which order backlogs are prohibited the basic monopoly model developed in sections i and ii of blinder s paper places no restriction upon the sign of inventory negative inventory is interpreted as net unfilled orders while no distinction is drawn between reductions in gross inventory and additions to the order backlog as a result the cost of holding inventory is symmetric around an arbitrary minimum point the only role of inventory is to permit the time paths of production and sales to differ gross inventory allows production to antedate sales while order backlogs generate revenue before production costs are borne under these circumstances if future costs and revenues are discounted it is natural to expect any stationary equilibrium level of net inventory to be negative this can be shown to be true of blinder s model it is useful to distinguish in general between the nonstochastic stationary level of inventory n and the stochastic stationary level n the former is realized when the current expected demand disturbance eo is zero and production equals sales the latter which differs from customary usage represents the level of inventory expected to prevail when adjustment to the current nonzero expected demand disturbance is complete if the demand disturbance is not a random walk so that p 1 in blinder s 5 the two equilibria coincide relatively little attention is devoted to either stationary solution because blinder s main interest is in the optimal current solution level n1 the stochastic stationary level is crucially important however since it represents the goal toward which the current choice must provide an optimal first step to verify that both nand n are negative whenever production is strictly positive note that blinder s necessary condition 7 with the coefficient cl set equal to zero together with the definition of xa as the deviation of the shadow value of inventory q from its nonstochastic stationary value q implies

rational expectations and the smoothing properties of inventories of finished goods abstract this paper formulates and estimates a dynamic rational expectations equilibrium model of inventories of finished goods and employment of labor the view that the primary role of inventories of finished goods is to act as a buffer stock in the face of fluctuating demand is examined both the model and estimation results indicate that this is the case because of differences in the costs involved for firms in changing their inventory stocks and labor force in addition to providing some new evidence on the behavior of inventories of finished goods and employment the paper illustrates a technology for maximum likelihood estimation of structural parameters under the hypothesis of rational expectations

inventories inflation dynamics and the new keynesian phillips curve abstract we introduce inventories into an otherwise standard new keynesian model and study the implications for inflation dynamics inventory holdings are motivated as a means to generate sales for demand constrained firms we derive various representations of the new keynesian phillips curve with inventories and show that one of these specifications is observationally equivalent to the standard model with respect to the behavior of inflation when the model s cross equation restrictions are imposed however the driving variable in the new keynesian phillips curve real marginal cost is unobservable and has to be proxied by for instance real unit labor cost an alternative approach is to impute marginal cost by using the model s optimality conditions we show that the stock sales ratio is linked to marginal cost we also estimate these various specifications of the new keynesian phillips curve using gmm we find that the predictive power of the inventory specification at best approaches that of the standard model but does not improve upon it

inventories and the volatility of production a stylized fact associated with inventory behavior is that the variance of production exceeds the variance of sales this paper presents a model of production decisions with demand uncertainty that incorporates no nnegativity constraints on inventories even with no productivity shocks optimal behavior by the firm is consistent with this stylized fact either if demand exhibits positive serial correlation or if the firm can backlog excess demand the reason is that a demand shock affects both the actual inventory level given unchanged production and the desired level production must replenish the stock and adjust to the new desired level copyright 1987 by american economic association

managing new and differentiated remanufactured products we study a firm that makes new products in the first period and uses returned cores to make remanufactured products along with new products in future periods the remanufactured product is differentiated from the new product so the firm needs to choose differentiated prices we analyze the monopoly environment in two period multi period three four and five and infinite planning horizons and characterize the optimal remanufacturing and pricing strategy for the firm in the process we identify remanufacturing savings thresholds that determine the production and pricing strategy for the firm among other results we find counter to intuition that in a finite horizon multi period setting the optimal policy is not necessarily monotone in remanufacturing savings

production smoothing evidence from physical product data we reconsider the paradox that the variance of production often exceeds the variance of shipments a result that casts doubt on the production smoothing model of inventory behavior most studies of production smoothing have analyzed two digit sic dollar value data from commerce department surveys in contrast this paper examines disaggregated physical product data and finds that production is smoother than shipments in about two thirds of the 38 industry or product groupings considered however doubts about the model persist most notably euler equation estimates of the model s cost parameters are usually imprecise and often do not have the signs postulated by production smoothing models

an empirical investigation of dynamic ordering policies adaptive base stock policy is a well known tool for managing inventories in nonstationary demand environments this paper presents empirical tests of this policy using aggregate firm level data first we extend a single item adaptive base stock policy in previous literature to a multi item case second we transform the policy derived for the multi item case to a regression model that relates firm level inventory purchases to firm level sales and changes in sales forecasts we focus on two research questions can the adaptive base stock policy explain cross sectional ordering behaviors under sales growth to the extent that the adaptive base stock policy fails to explain ordering behaviors under sales growth are there frictions that explain such a finding our empirical results demonstrate disparities in ordering behaviors between firms experiencing high and moderate sales growth contrary to theoretical prediction this implies that inventory purchases are a function of not only current sales and changes in sales forecast but also past sales growth as potential explanations for this departure from theoretical prediction we show that both future demand dynamics and inventory holding risks depend on past sales growth in addition we find that firms inventory holding risks may also be affected by purchasing constraints imposed by supply chain contracts our results provide managerial implications for practitioners and inform future theoretical research this paper was accepted by martin lariviere operations management

on the stability of supply chains this paper examines the stability of decentralized multistage supply chains under arbitrary demand conditions it looks for intrinsic properties of the inventory replenishment policies that hold for all customer demand processes and for policies with desirable properties it is found that the overall conditions experienced by suppliers several stages removed from the final customer e g the variances of the orders they receive and the inventories they keep depend on the policy much more than on the demand process a policy specific but demand independent upper bound for the order variance amplification factor of any decentralized policy is shown to exist and its formula is presented the bound is always tight for the suppliers at the end of a long chain so that a policy exhibits the bullwhip effect if and only if its bound is greater than 1 a simple necessary condition for bullwhip avoidance is also identified in terms of a policy s gain gain is the marginal change in average inventory induced by a policy when there is a small but sustained change in the demand rate it is shown thatall policies with positive gain produce the bullwhip effect if they do not use future order commitments because manufacturers can reduce costs by operating with positive gain this explains the prevalence of the bullwhip effect a family of commitment based policies that can dynamically maintain any desired inventory level for any demand rate e g achieve positive gain without the bullwhip effect is also presented the family includes just in time strategies as a special case simulation results are used as an illustration

a high tech product market share model with customer expectations in a product category based on dynamic technology new products enter the market in rapid succession and the competitive situation changes almost daily because technological features of available products tend to improve while prices tend to decline customers develop expectations that may influence their purchase decisions we model the impact of customer expectations regarding price and technology on product market share in the personal computer industry finding significant nonlinear effects of both these effects are observed when actual product price and or technology differ from expectations by a threshold amount our results suggest implementable implications for high tech product managers in particular price and technology should meet but not exceed customer expectations this does not mean that managers should strive for mediocrity rather continuous improvement should be implemented so that product development efforts lead customer expectations

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

the interactive and causal relationships involving precious metal price movements an analysis of the gold and silver markets to explain the interactive and causal relationships between gold and silver price movements time series procedures are used to identify reduced form parameters corresponding to a general arbitrage model enveloped in a framework of expectations about capital gains current price changes are conjectured to be functions of lagged and present values of the substitute precious metal prices and the interest rate plus lagged values of its own price to determine the appropriate number of lags to identify the appropriate interaction and to examine the exogeneity between the gold and silver prices and the rate of interest we use schwarz s bayesian information criterion and akaike s final prediction error criterion the resultant estimated model is simultaneous and provides information on participants average lead times in forming these expectations

a dynamic it adoption model for the soho market pc generational decisions with technological expectations thesmall office home office soho professionals comprise the fastest growing segment in the labor force today typically being a one person business based at home soho owners mostly rely on office information technology to single handedly run their entire operation despite the segment s ostensibly growing dependence and influence on the information technology it industry still very little is known about the dynamics between soho and it products with the purpose of addressing this void we investigate the soho professionals adoption patterns of multigenerational it products accordingly we develop and empirically estimate an individual soho levelinitial andrepeat purchase logit model that captures the procurement patterns for successive generations of technological products namely the pc category specifically we find that soho professionals procurement choices are influenced by a number of salient dimensions i e income performance price interpurchase time network externalities furthermore some soho owners are found to have a preference for a future expected generation over a currently available one which is explained via their business dispositions i e technology orientation result orientation search orientation toward accepting technological incertitude

a panel data study on spanish firms inventory investment this paper raises several questions about inventory investment of a sample of 172 big nonfinancial spanish companies inventory investment has been usually explained by two alternative theories the production smoothing model and the s s model first we provide a descriptive analysis based on industry level data to show some shortcomings of the first model then we test a flexible accelerator model using firm level data the results seem to show that inventory investment previous period inventories and sales are closely and significantly related this evidence although not conclusive rejects both the pure production smoothing model and the s s model at the same time our results confirm the view of a target inventory level and the plausibility of the so called stock adjustment model so that the optimal inventory holding buffers sales volatility

the bullwhip effect in capacitated supply chains with consideration for product life cycle aspects abstract this paper presents an analysis of the bullwhip effect and net stock amplification in a three echelon supply chain considering step changes in the production rates during a product s life cycle demand the analysis is focused around highly complex and engineered products e g automobiles that have relatively long production life cycles and require significant capital investment in manufacturing using a simulation approach we analyze three stages of the product life cycle including low volumes during product introduction peak demand and eventual decline toward the end of the life cycle parts of the simulation model have been adopted by a major north american automotive oem as part of a scenario analysis tool for strategic supply network design and analysis the simulation results show that performance of a system as a whole deteriorates when there is a step change in the life cycle demand while restriction in production capacity does not significantly impact the bullwhip effect it increases the net stock amplification significantly for the supply chain setting under consideration furthermore a number of important managerial insights are presented based on sensitivity analysis of interaction effect of capacity constraints with other supply chain parameters

a generalized ordering and recovery policy for reusable items this paper deals with a joint eoq and epq model in which a stationary demand is satisfied by recovered products as well as newly purchased products it is assumed that a fixed proportion of the used products are collected from customers and later recovered for reuse we generalize the p r policy in the literature by treating the sequence of orders for newly purchasing products and setups for recovery process within a cycle as a decision variable through example problems we illustrate the validity of the model and solution procedure developed

investment under uncertainty the case of replacement investment decisions we analyze the determinants of replacement investment decisions in a contingent claims model with maintenance and operation cost uncertainty we find that the optimal time between replacements is increasing in the volatility of cost the purchase price of a new asset and the corporate tax rate and is decreasing in the systematic risk of cost the salvage value of the asset and the investment tax credit the optimal time between replacements can either increase or decrease with an increase in the depreciation rate extensions of the model to examine the effects of technological and tax policy uncertainty on replacement investment decisions give intuitive but striking results uncertainty about the arrival of a technological innovation that would decrease maintenance and operation cost results in a significant decrease in replacement investment uncertainty in a tax law change that would encourage investment decreases current investment and uncertainty in a tax law change that would discourage investment increases current investment

a diffusion theory model of adoption and substitution for successive generations of high technology products this study deals with the dynamic sales behavior of successive generations of high technology products new technologies diffuse through a population of potential buyers over time therefore diffusion theory models are related to this demand growth furthermore successive generations of a technology compete with earlier ones and that behavior is the subject of models of technological substitution building upon the bass bass f m 1969 a new product growth model for consumer durables management sci 15january 215 227 diffusion model we develop a model which encompasses both diffusion and substitution we demonstrate the forecasting properties of the model by estimating parameters over part of the data and projecting shipments for later periods

bullwhip effect measurement and its implications the bullwhip effect or demand information distortion has been a subject of both theoretical and empirical studies in the operations management literature in this paper we develop a simple set of formulas that describe the traditional bullwhip measure as a combined outcome of several important drivers such as finite capacity batch ordering and seasonality our modeling framework is descriptive in nature as it features certain plausible approximations that are commonly employed in practical inventory systems the results are nonetheless compelling and can be used to explain various conflicting observations in previous empirical studies building on the theoretical framework we discuss the managerial implications of the bullwhip measurement we show that the measurement can be completely noninformative about the underlying supply chain cost performance if it is not linked to the operational details such as decision intervals and leadtimes specifically we show that an aggregated measurement over relatively long time periods can mask the operational level bullwhip in addition we show that masking also exists under product or location aggregation in some illustrative cases

equilibrium adjustment with endogenous information and inventories the paper analyzes the interaction of information acquisition and inventory flexibility with industry adjustment to imperfectly perceived cost and demand disturbances improved information about disturbances reduces the extent to which disturbances are unperceived and dampens the use of inventories reduced inventory flexibility induces firms to devote more resources to acquiring information about disturbances the analysis demonstrates how equilibrium price and output adjustment depend endogenously on the degree of inventory flexibility and other structural parameters influencing the acquisition of information in this paper we analyze how endogenous information acquisition and inventory flexibility influence price and output adjustment in a competitive industry we focus on the potential substitutability of information acquisition for inventory flexibility when disturbances are imperfectly perceived by individual firms the analysis highlights the general issue of how market adjustment depends on structural parameters that influence agents incentives to acquire information there are several reasons why information acquisition may play a role in market adjustment first the rapid development of information technology has enabled firms to gather and process data relevant to production and sales decisions from a greater number of external and internal sources this trend has reduced the costs of forecasting and monitoring factors influencing production and demand conditions for the individual firm relative to those of its competitors as well as for the industry as a whole in particular it has permitted quicker awareness of changing customer demand as well as greater control of the flow of inputs and intermediate goods during the production process this implies that the resources devoted to information acquisition and processing have come to play an important role in firm decisions 2 second improved information about demand and cost conditions may affect the function of inventories inventory adjustment allows a firm s production costs to be smoothed in response to anticipated movements in demand and costs and to be buffered against unanticipated disturbances see ashley and orr 1985 thus

can the production smoothing model of inventory behavior be saved the production smoothing model of inventory behavior has a long and venerable history and theoretical foundations that seem very strong yet certain overwhelming facts seem not only to defy explanation within the production smoothing framework but actually to argue that the basic idea of production smoothing is all wrong most prominent among these is the fact that the variance of detrended production exceeds the variance of detrended sales this paper first documents the stylized facts then it derives the production smoothing model rigorously and explains how the model can be amended to make it consistent with the facts finally it reviews the theoretical and empirical evidence and tries to draw some tentative conclusions

economic order quantity for growing items abstract economic order production quantity eoq epq models have generally been presented for manufacturing products incorporating some important features of a specific category of products different eoq epq models have been proposed in literature this study proposes a new class of inventory models i e a model for a specific type of inventory items growing items poultry and livestock are good examples of growing inventory items we begin by proposing a general mathematical model which can be used for different types of growing items followed by a particular mathematical model for a specific type of poultry we calculate the optimal order quantity of the growing items at the start of a growing cycle the optimal length of the growing cycle and the optimal total profit numerical examples are provided for a type of poultry to illustrate the model a sensitivity analysis is presented to study the effect of the main parameters of the model in terms of its decision variables and objective function the results of the sensitivity analysis suggest that production costs are the most crucial parameter

characterization of the bullwhip effect in linear time invariant supply chains some formulae and tests the authors analyze the bullwhip effect in multistage decentralized supply chains operated with linear and time invariant inventory management policies the focus is on robustness the supply chain is modeled as a single input single output control system driven by arbitrary customer demands the authors derive robust analytical conditions to predict the presence of the bullwhip effect and bound its magnitude based only on the way inventories are managed these results hold independently of the customer demand the authors also characterize the stream of orders placed at any stage of the chain when the customer demand process is known and ergodic and give an exact formula for the variance of the orders placed this formula generalizes existing results by broadening the class of inventory replenishment policies and customer demand processes to which it applies the authors also show that the bullwhip effect can be mitigated by introducing commitments for future orders into the ordering policies

measuring and avoiding the bullwhip effect a control theoretic approach an important contributory factor to the bullwhip effect i e the variance amplification of order quantities observed in supply chains is the replenishment rule used by supply chain members first the bullwhip effect induced by the use of different forecasting methods in order up to replenishment policies is analysed variance amplification is quantified and we prove that the bullwhip effect is guaranteed in the order up to model irrespective of the forecasting method used thus when production is inflexible and significant costs are incurred by frequently switching production quantities up and down order up to policies may no longer be desirable or even achievable in the second part of the paper a general decision rule is introduced that avoids variance amplification and succeeds in generating smooth ordering patterns even when demand has to be forecasted the methodology is based on control systems engineering and allows important insights to be gained about the dynamic behaviour of replenishment rules

financing constraints and inventories abstract this paper investigates the impact of financing constraints on firms inventory and cash management in particular it examines the extent to which the presence of such constraints may account for certain empirical regularities these include e g the excess variance of production vis a vis that of sales as well as the counter cyclicality and persistence of the inventory sales ratio we model the intertemporal decision making on production cash retention and dividends of a firm that is exposed to stochastic demand shocks in every period and faces constrained access to external sources of finance it is found that the presence of financing constraints can explain the excess variance of production in a model which otherwise would not deliver this result moreover as long as demand is positively serially correlated they also contribute to the counter cyclicality and persistence of the inventory sales ratio the paper suggests that financing constraints should not be discarded as a factor driving the cyclical behaviour of inventories