assortment planning and inventory decisions under stockout based substitution we present an efficient dynamic programming algorithm to determine the optimal assortment and inventory levels in a single period problem with stockout based substitution in our model total customer demand is random and comprises fixed proportion of customers of different types customer preferences are modeled through the definition of these types each customer type corresponds to a specific preference ordering among products a customer purchases the highest ranked product according to his type if any that is available at the time of his visit to the store stockout based substitution we solve the optimal assortment problem using a dynamic programming formulation we establish structural properties of the value function of the dynamic program that in particular help to characterize multiple local maxima we use the properties of the optima to solve the problem in pseudopolynomial time our algorithm also gives a heuristic for the general case i e when the proportion of customers of each type is random in numerical tests this heuristic performs better and faster than previously known methods especially when the mean demand is large the degree of substitutability is high the population is homogeneous or prices and or costs vary across products

optimizing multinomial logit profit functions the multinomial logit model is a standard approach for determining the probability of purchase in product line problems when the purchase probabilities are multiplied by product contribution margins the resulting profit function is generally nonconcave because of this standard nonlinear search procedures may terminate at a local optimum which is far from the global optimum we present a simple procedure designed to alleviate this problem the key idea of this procedure is to find a path of prices from the global optimum of a related but concave logit profit function to the global optimum of the true but nonconcave logit profit function

conditions that cause risk pooling to increase inventory abstract we say product a is a partial substitute for product b if a fraction of the customers who prefer b are willing to accept a when b is out of stock when demand is uncertain it is intuitive and true that a larger willing to substitute fraction implies larger expected profits a higher willing to substitute fraction allows one to pool the risk of individual products it may also be intuitive that a larger willing to substitute fraction might result in lower optimal total inventory for the full substitution structure several researchers have shown that for certain distributions such as the exponential this latter intuition is not true we show that this full substitution anomaly can occur with any right skewed demand distribution we assume i i d demand distributions unless we indicate otherwise we also show that the anomaly can occur for a number of realistic situations of partial substitution with commonly used demand distributions such as normal exponential poisson and uniform we also demonstrate the anomaly for more than one period with backlogging lost sales more than two products and with setup costs

has the median voter found a ballot box that he can control this paper examines the appropriateness of the median voter hypothesis within an agenda control framework where the alternative to a proposed expenditure level is the existing level evidence from new york state school districts suggests that within this institutional setting the actual level of public service provision does not differ significantly from the median voter s preferred level the evidence also suggests that demand function parameter estimates for educational expenditures are not sensitive to the assumption that the public service output level corresponds to the median voter s private equilibrium

a market discovery algorithm to estimate a general class of nonparametric choice models we propose an approach for estimating customer preferences for a set of substitutable products using only sales transactions and product availability data the underlying demand framework combines a general nonparametric discrete choice model with a bernoulli process of arrivals over time the choice model is defined by a discrete probability mass function pmf on a set of possible preference rankings of alternatives and it is compatible with any random utility model an arriving customer is assumed to purchase the available option that ranks highest in her preference list the problem we address is how to jointly estimate the arrival rate and the pmf of the rank based choice model under a maximum likelihood criterion since the potential number of customer types is factorial we propose a market discovery algorithm that starts with a parsimonious set of types and enlarge it by automatically generating new types that increase the likelihood value numerical experiments confirm the potential of our proposal for a realistic data set in the hospitality industry our approach improves the root mean square errors between predicted and observed purchases computed under independent demand model estimates by 67 to 93 this paper was accepted by serguei netessine operations management

single period multiproduct inventory models with substitution we study a single period multiproduct inventory problem with substitution and proportional costs and revenues we consider n products and n demand classes with full downward substitution i e excess demand for class i can be satisfied using product j for i j we first discuss a two stage profit maximization formulation for the multiproduct substitution problem we show that a greedy allocation policy is optimal we use this to write the expected profits and its first partials explicitly this in turn enables us to prove additional properties of the profit function and several interesting properties of the optimal solution in a limited computational study using two products we illustrate the benefits of solving for the optimal quantities when substitution is considered at the ordering stage over similar computations without considering substitution while ordering specifically we show that the benefits are higher with high demand variability low substitution cost low profit margins or low price to cost ratio high salvage values and similarity of products in terms of prices and costs

inventory competition for newsvendors under the objective of profit satisficing abstract inventory competition for newsvendors nvs has been studied extensively under the objective of expected profit maximization which is based on risk neutrality in this paper we study this classic problem under the objective of profit satisficing which is based on downside risk aversion consistent with prior literature we consider two possible scenarios in the first scenario each nv s demand depends on the stocking levels of all nvs other than herself in this scenario we show that there is a unique nash equilibrium where all nvs optimally order as if they were independent in the second scenario each nv s demand depends on the stocking levels of all nvs including herself we prove the existence of nash equilibrium for both additive and multiplicative forms of demands as a special case we also study symmetrical nvs under the proportional allocation model we show that at equilibrium if the number of nvs exceeds a threshold the market becomes highly competitive

green revolution in sub saharan africa implications of imposed innovation for the wellbeing of rural smallholders green revolution policies are again being pursued to drive agricultural growth and reduce poverty in sub saharan africa however conditions have changed since the well documented successes of the 1960s and 1970s benefitted smallholders in southern asia and beyond we argue that under contemporary constraints the mechanisms for achieving improvements in the lives of smallholder farmers through such policies are unclear and that both policy rationale and means of governing agricultural innovation are crucial for pro poor impacts to critically analyze rwanda s green revolution policies and impacts from a local perspective a mixed methods multidimensional wellbeing approach is applied in rural areas in mountainous western rwanda here malthusian policy framing has been used to justify imposed rather than induced innovation the policies involve a substantial transformation for rural farmers from a traditional polyculture system supporting subsistence and local trade to the adoption of modern seed varieties inputs and credit in order to specialize in marketable crops and achieve increased production and income although policies have been deemed successful in raising yields and conventionally measured poverty rates have fallen over the same period such trends were found to be quite incongruous with local experiences disaggregated results reveal that only a relatively wealthy minority were able to adhere to the enforced modernization and policies appear to be exacerbating landlessness and inequality for poorer rural inhabitants negative impacts were evident for the majority of households as subsistence practices were disrupted poverty exacerbated local systems of knowledge trade and labor were impaired and land tenure security and autonomy were curtailed in order to mitigate the effects we recommend that inventive pro poor forms of tenure and cooperation none of which preclude improvements to input availability market linkages and infrastructure may provide positive outcomes for rural people and importantly in rwanda for those who have become landless in recent years we conclude that policies promoting a green revolution in sub saharan africa should not all be considered to be pro poor or even to be of a similar type but rather should be the subject of rigorous impact assessment such assessment should be based not only on consistent objective indicators but pay attention to localized impacts on land tenure agricultural practices and the wellbeing of socially differentiated people

a nonparametric approach to modeling choice with limited data choice models today are ubiquitous across a range of applications in operations and marketing real world implementations of many of these models face the formidable stumbling block of simply identifying the right model of choice to use because models of choice are inherently high dimensional objects the typical approach to dealing with this problem is positing a priori a parametric model that one believes adequately captures choice behavior this approach can be substantially suboptimal in scenarios where one cares about using the choice model learned to make fine grained predictions one must contend with the risks of mis specification and overfitting underfitting thus motivated we visit the following problem for a generic model of consumer choice namely distributions over preference lists and a limited amount of data on how consumers actually make decisions such as marginal information about these distributions how may one predict revenues from offering a particular assortment of choices an outcome of our investigation is a nonparametric approach in which the data automatically select the right choice model for revenue predictions the approach is practical using a data set consisting of automobile sales transaction data from a major u s automaker our method demonstrates a 20 improvement in prediction accuracy over state of the art benchmark models this improvement can translate into a 10 increase in revenues from optimizing the offer set we also address a number of theoretical issues among them a qualitative examination of the choice models implicitly learned by the approach we believe that this paper takes a step toward automating the crucial task of choice model selection this paper was accepted by yossi aviv operations management

optimizing retail assortments retailers face the problem of finding the assortment that maximizes category profit this is a challenging task because the number of potential assortments is very large when there are many stock keeping units skus to choose from moreover sku sales can be cannibalized by other skus in the assortment and the more similar skus are the more this happens this paper develops an implementable and scalable assortment optimization method that allows for theory based substitution patterns and optimizes real life large scale assortments at the store level we achieve this by adopting an attribute based approach to capture preferences substitution patterns and cross marketing mix effects to solve the optimization problem we propose new very large neighborhood search heuristics we apply our methodology to store level scanner data on liquid laundry detergent the optimal assortments are expected to enhance retailer profit considerably 37 3 and this profit increases even more to 43 7 when sku prices are optimized simultaneously

joint inventory and pricing decisions for an assortment we seek optimal inventory levels and prices of multiple products in a given assortment in a newsvendor model single period stochastic demand under price based substitution but not stockout based substitution we address a demand model involving multiplicative uncertainty motivated by market share models often used in marketing the pricing problem that arises is known not to be well behaved in the sense that in its deterministic version the objective function is not jointly quasi concave in prices however we find that the objective function is still reasonably well behaved in the sense that there is a unique solution to the first order conditions and this solution is optimal for our problem

bundle pricing of inventories with stochastic demand we consider a retailer selling a fixed inventory of two perishable products over a finite horizon assuming poisson arrivals and a bivariate reservation price distribution we determine the optimal product and bundle prices that maximize the expected revenue our results indicate that the performances of mixed bundling pure bundling and unbundled sales strategies heavily depend on the parameters of the demand process and the initial inventory levels bundling appears to be most effective with negatively correlated reservation prices and high starting inventory levels when the starting inventory levels are equal and in excess of average demand most of the benefits of bundling can be achieved through pure bundling however the mixed bundling strategy dominates the other two when the starting inventory levels are not equal we also observe that an incorrect modeling of the reservation prices may lead to significant losses the model is extended to allow for price changes during the selling horizon it is shown that offering price bundles mid season may be more effective than changing individual product prices

the growth of social security electoral push or political pull the growth of social security electoral push or political pull i introduction during the post world war ii period the social security program was among the fastest growing programs in the federal budget surpassing defense spending as the largest category of expenditures in the mid seventies the program which disbursed only 132 million dollars in 1942 disbursed more than 156 billion dollars forty years late a thousand fold increase as a consequence of this growth and the program s recent financial problems a number of economists have turned their attention to the economics of social security recent examples include kahn 1988 boskin et al 1987 and veall 1986 yet only weaver 1982 and turner 1984 attempt to analyze the growth of the social security program weaver s legislative history of the program suggests that special interest groups had a major impact on social security programs turner argues that program benefit levels are affected by demographic changes which affect the cost of intergenerational redistribution in this paper we use the public choice approach to explain increases in benefit levels from 1946 1980 we develop and test three alternative public choice models of the politics of retirement benefit levels our analysis thus sheds light on an important question neglected by previous research have social security expenditures grown because special interest groups have effectively captured the congress or is congress simply responding to demands placed on it by the electorate the answer to this question is relevant to normative analysis of existing programs and to alternative proposals for reform in addition our study of the principal determinants of the growth of program benefit levels serves as an event study for assessing the merits of alternative theories of political decision making borcherding 1985 discusses two public choice explanations for the growth of public expenditures first public programs may expand as a result of the voting rules which underlie the political process when decisions are made by majority rule an increase in the median voter s demand for public services tends to increase public service levels because prospective candidates will revise their policy positions in order to be elected the wagner 1958 hypothesis for example maintains that increases in real income cause individuals to prefer both absolutely and relatively larger public expenditures borcherding notes that about 40 percent of the rate at which public sector spending has replaced private sector spending over the past eighty years can be explained with a median voter approach such an approach does better in what borcherding calls traditional areas of public expenditure where a median voter model can account for about 73 percent of the rate at which public expenditures excluding transfers have displaced private expenditures the median voter might favor public transfers to the elderly for two reasons first he may have an interdependent utility function in which the plight of the elderly poor arouses a charitable response while the redistribution from young to old does not simply target the old poor as a group the elderly do seem to be relatively less wealthy than the middle aged and the yound if one considers the average capitalized value of future income receipts from labor and capital second to the extent that the social security program offers a connection between reductions in current consumption and increases in future consumption it is a rather complex savings and insurance program the median voter s motivation for transferring monies to today s elderly may be a vehicle for ensuring future transfers to himself while this explanation is difficult to motivate at the individual level since a savings program for future retirement need not pay anything to today s elderly a continuing program of tax funded transfers is plausible method of establishing the moral constitution necessary to ensure that future transfers do in fact take place

tomatoes land and hearsay property and history in asante in the time of structural adjustment abstract after a decade of advocating market based solutions to poverty and underdevelopment in sub saharan africa policy analysts have begun to reexamine the actual and potential role of african states and institutions in promoting sustainable development while stressing the importance of flexibility in policies and institutions much of this debate rests on ahistorical approaches to understanding african institutions which portray them as inflexible and fragile beleaguered by economic and political change rather than contributing to it after reviewing some of the assumptions which inform recent debates this essay argues for a more processual approach which takes account of the negotiability and ambiguity of many institutional arrangements drawing on a case study of recent changes in land rights and agricultural practices in a rural community in ghana

a static approximation for dynamic demand substitution with applications in a competitive market we propose a static approximation of dynamic demand substitution behavior based on a fluid network model and a service inventory mapping this approximation greatly enhances our ability to analyze the interdependent inventory service price and product assortment decisions in noncompetitive and competitive scenarios with demand substitution we demonstrate that the approximation is well behaved and then apply it to two previously intractable applications first we study a price and service competition between single product retailers after establishing a unique pure strategy nash equilibrium we find that competition results in lower price higher demand and a higher level of inventory we also observe that the aggregate profit and inventory level increase to positive constants as the number of retailers goes to infinity second we study a duopolistic competition on price service and product assortment we establish a pure strategy nash equilibrium for the product assortment competition and identify a condition for uniqueness we find that competition on both price and product assortment results in lower price and less variety for each competitor but the total number of products and the aggregate inventory level in a duopoly market are both likely to be higher than in a monopolistic market

dynamic assortment with demand learning for seasonal consumer goods companies such as zara and world co have recently implemented novel product development processes and supply chain architectures enabling them to make more product design and assortment decisions during the selling season when actual demand information becomes available how should such retail firms modify their product assortment over time in order to maximize overall profits for a given selling season focusing on a stylized version of this problem we study a finite horizon multiarmed bandit model with several plays per stage and bayesian learning our analysis involves the lagrangian relaxation of weakly coupled dynamic programs dps results contributing to the emerging theory of dp duality and various approximations it yields a closed form dynamic index policy capturing the key exploration versus exploitation trade off and associated suboptimality bounds in numerical experiments its performance proves comparable to that of other closed form heuristics described in the literature but this policy is particularly easy to implement and interpret this last feature enables extensions to more realistic versions of the motivating dynamic assortment problem that include implementation delays switching costs and demand substitution effects

household strategies and rural livelihood diversification this article reviews the recent literature on diversification as a livelihood strategy of rural households in developing countries with particular reference to sub saharan africa livelihood diversification is defined as the process by which rural families construct a diverse portfolio of activities and social support capabilities in order to survive and to improve their standards of living the determinants and effects of diversification in the areas of poverty income distribution farm output and gender are examined some policy inferences are summarised the conclusion is reached that removal of constraints to and expansion of opportunities for diversification are desirable policy objectives because they give individuals and households more capabilities to improve livelihood security and to raise living standards

an integrated assortment and shelf space optimization model with demand substitution and space elasticity effects abstract retailers must define their assortments and assign shelf space to the items included in these assortments these two planning problems are mutually dependent if space is scarce we formulate a model that maximizes a retailer s profit by selecting the optimal assortment and assigning limited shelf space to items this model is the first decision model to integrate assortment and shelf space planning by considering stochastic and space elastic demand out of assortment and out of stock substitution effects to solve the model we develop a specialized heuristic that efficiently yields near optimal results even for large scale problems we show that our approach outperforms alternative approaches e g a sequential planning approach that first picks assortments and then assigns shelf space by up to 18 and a greedy algorithm by up to 16 in terms of profit we test our model on two real data sets for perishable and non perishable items and show how it can support retailers in increasing their profits by up to 25 we then use the model to generalize these results and find that space elasticity and substitution effects have a significant impact on profits assortment size as well as facing decisions and that both effects reinforce each other using our model we finally derive rules of thumb for planners in practice

the causes of government expenditure growth a survey of the u s evidence abstract the growth of government budgets can be broken down into a institutional and institutional components the former component the familiar substitution income and population public goods tax sharing effects is estimated to contribute about two fifths of the growth of u s government spending the latter component rent seeking political redistributions bureaucracy and perceptual informational impedimentia is important too but an exact imputation cannot be asserted given the state of the art in empirical public choice theory the cross effects on spending of the growth of regulation and tax preferences or tax expenditures though interesting is not pursued

category management and coordination in retail assortment planning in the presence of basket shopping consumers this paper studies the assortment planning problem with multiple merchandise categories and basket shopping consumers i e consumers who desire to purchase from multiple categories we present a duopoly model in which retailers choose prices and variety level in each category and consumers make their store choice between retail stores and a no purchase alternative based on their utilities from each category the common practice of category management cm is an example of a decentralized regime for controlling assortment because each category manager is responsible for maximizing his or her assigned category s profit alternatively a retailer can make category decisions across the store with a centralized regime we show that cm never finds the optimal solution and provides both less variety and higher prices than optimal in a numerical study we demonstrate that profit loss due to cm can be significant finally we propose a decentralized regime that uses basket profits a new metric rather than accounting profits basket profits are easily evaluated using point of sale data and the proposed method produces near optimal solutions

ideological conviction and persuasion in the rent seeking society abstract the paper develops a model of rent seeking in a democratic political context where voting as well as rent seeking matters in this context the paper demonstrates that voter ideology is a constraint on the rent seeking game as well as a possible avenue of rent seeking in a setting where there are both rent seeking and ideological interest groups rent seekers can free ride on the efforts of ideologues which tends to reduce rent seeking effort in a setting where complementary economic and ideological interest groups coordinate their efforts both rent seeking and ideological conflict tend to increase

assortment optimization under variants of the nested logit model we study a class of assortment optimization problems where customers choose among the offered products according to the nested logit model there is a fixed revenue associated with each product the objective is to find an assortment of products to offer so as to maximize the expected revenue per customer we show that the problem is polynomially solvable when the nest dissimilarity parameters of the choice model are less than one and the customers always make a purchase within the selected nest relaxing either of these assumptions renders the problem np hard to deal with the np hard cases we develop parsimonious collections of candidate assortments with worst case performance guarantees we also formulate a convex program whose optimal objective value is an upper bound on the optimal expected revenue thus we can compare the expected revenue provided by an assortment with the upper bound on the optimal expected revenue to get a feel for the optimality gap of the assortment by using this approach our computational experiments test the performance of the parsimonious collections of candidate assortments that we develop

the rise of the modern welfare state ideology institutions and income security analysis and evidence in the 25 year period between 1960 and 1985 there was a great expansion of welfare state programs throughout the west the fraction of gdp accounted for by social expenditures doubled in much of europe and grew by 40 50 in many other oecd nations after 1985 growth in social insurance programs slowed relative to other parts of the economy this paper explores the extent to which institutions and ideological shifts may have accounted for the period of rapid growth for differences in the extent of that growth and for the subsequent reduction in the growth rates of social insurance programs

interpreting changes from the 1970s to the 1990s in african agriculture through village studies abstract assessments of the performance of agriculture in sub saharan africa are typically based on official production statistics at national level between the early 1970s and the mid 1990s these often show alarmingly poor rates of growth but there are good reasons to doubt the statistics and their interpretation an alternative is to examine the record from the village level upward this paper looks at the evidence from 26 case studies of change between the mid 1970s and the mid 1980s at the district or village level these suggest less cause for alarm than the national statistics they confirm that access to markets is essential for agricultural development the single biggest idea in the policy reforms of the 1980s but they also underline the importance of the detail of policy in remedying failures in product capital and insurance markets and in public investment in technology

the rhetoric and reality of redistribution it is customary when giving a presidential address to begin by remarking on how happy you feel i have an even stronger reason for being happy than most presidents it will at long last permit me to break into the southern economic journal up to this point referees of that august institution have always rejected everything that i sent them finally however i am privileged to put an unrefereed paper in the journal and hence do not have to worry about this one being rejected the audience may feel that although it is nice for me it is hard on the journal but under the sacred traditions of the southern economic association the editors and referees can do nothing about it the blame if there is any has to be laid on me and not on the management of the journal in a way the fact that i will not face referees is important because in this paper i propose to violate a number of implicit taboos in the discussion of income redistribution indeed i propose to argue that most of the current discussion of income redistribution is drastically defective this will not only include rawls it will include what most members of the economic profession normally say on the subject and presumably what the potential referees of this paper would have thought let me very briefly survey the existing economic as opposed to the philosophic literature on the redistribution of income firstly a good many economists have said simply that economics can say nothing about the subject because somebody gains and somebody loses but we can t say whether this is a good or a bad thing with our apparatus hochman and rodgers 9 have started another tradition of dealing with income redistribution in which the government is seen as simply organizing what is essentially a voluntary transfer from the better off american citizens to the less well off american citizens why the government should be used as an instrumentality for this kind of transfer was interestingly enough first explained by milton friedman 6 191 92 such redistribution has the interesting characteristic that it does not actually involve redistribution because the people who make the gift are maximizing their own utility and hence are better off it is a case in which human preferences are so arranged that a given dollar of income benefits two people a full dollar s worth the donor gains a dollar from expending money at its best use to him i e making a gift to the poor and the poor gain the dollar in a somewhat metaphysical sense it can be said here

the assortment packing problem multiperiod assortment planning for short lived products motivated by retailers frequent introduction of new items to refresh product lines and maintain their market shares we present the assortment packing problem in which a firm must decide in advance the release date of each product in a given collection over a selling season our formulation models the trade offs among profit margins preference weights and limited life cycles a key aspect of the problem is that each product is short lived in the sense that once introduced its attractiveness lasts only a few periods and vanishes over time the objective is to determine when to introduce each product to maximize the total profit over the selling season even for two periods the corresponding optimization problem is shown to be np complete as a result we study a continuous relaxation of the problem that approximates the problem well when the number of products is large when margins are identical and product preferences decay exponentially its solution can be characterized it is optimal to introduce products with slower decays earlier the structural properties of the relaxation also help us to develop several heuristics for which we establish performance guarantees we test our heuristics with data on sales and release dates of women s handbags from an accessories retailer the numerical experiments show that the heuristics perform very well and can yield significant improvements in profitability this paper was accepted by yossi aviv operations management

an efficient algorithm for capacitated assortment planning with stochastic demand and substitution abstract the ever increasing product variety in grocery retailing is in conflict with the limited shelf space managing the assortment and regular order quantity for perishable and non perishable products is therefore a core task for retailers retailers want to maximize profit by considering potential revenues purchase costs diminishing profits for products and opportunity costs for unfulfilled demand when determining assortment sizes and order volume to meet stochastic consumer demand we considered a newsvendor based decision model that jointly optimizes assortment size and the associated order volumes for listed items the model considers out of assortment ooa and out of stock oos substitution effects the model is a structural equivalent to the model described in kok and fisher 2007 and solved there via a heuristic procedure we develop an optimal solution procedure and a time efficient heuristic that solves the model the heuristic suggested is applicable for practically relevant large scale problem instances numerical tests reveal that the heuristic procedure produces close to optimal solutions and outperforms the kok and fisher heuristic with regard to both computational time and solution quality a simulation study with discrete demand justifies our approach with using continuous demand distributions the numerical analyses show that considering substitution effects in a decision based model has a significant impact on the total profit and solution structure further managerial insights are presented with regard to assortment heterogeneity when shelf size substitution and demand variability are varied

determinants of local school spending some consistent estimates the traditional median voter model predicts that median income and taxprice are the primary determinants of local school spending levels it further implies that lump sum grants wills be utilized like private income and thus income and grant coefficients should be the same our comprehensive search technique shows that excluding equalized assessed value these predictions hold up quite well over 2048 specifications income and taxprice elasticities are reasonable and tightly distributed with income and blockgrant effects of the same general size as note above any hint of flypaper effect is completely dependent on the inclusion of equalized assessed value in the regression equation since the state of new york has annual district level tax levy elections it would be hard to rationalize bureaucratic power or agenda control as capable of producing flypaper type effects so this absence is not surprising future research should 1 investigate the specification sensitivity of flypaper effects with other datasets and wealth variables and 2 examine election and tax rules for the possibility of budget maximizing actions by school officials finally the consistently positive effects of private schooling nonwhite and in poverty suggest that future work should attempt to model non linear income effects

stocking retail assortments under dynamic consumer substitution we analyze a single period stochastic inventory model newsboy like model in which a sequence of heterogeneous customers dynamically substitute among product variants within a retail assortment when inventory is depleted the customer choice decisions are based on a natural and classical utility maximization criterion faced with such substitution behavior the retailer must choose initial inventory levels for the assortment to maximize expected profits using a sample path analysis we analyze structural properties of the expected profit function we show that under very general assumptions on the demand process total sales of each product are concave in their own inventory levels and possess the so calleddecreasing differences property meaning that the marginal value of an additional unit of the given product is decreasing in the inventory levels of all other products for a continuous relaxation of the problem we then show via counterexamples that the expected profit function is in general not even quasiconcave thus global optimization may be difficult however we propose and analyze a stochastic gradient algorithm for the problem and prove that it converges to a stationary point of the expected profit function under mild conditions finally we apply the algorithm to a set of numerical examples and compare the resulting inventory decisions to those of some simpler naive heuristics the examples show that substitution effects can have a significant impact on an assortment s gross profits the examples also illustrate some systematic distortions in inventory decisions if substitution effects are ignored in particular under substitution one should stock relatively more of popular variants and relatively less of unpopular variants than a traditional newsboy analysis indicates

the multi item newsvendor model with cross selling and the solution when demand is jointly normally distributed abstract products are often demanded in tandem because of the cross selling effect the demand for an item can increase if sales of its cross selling associated items are achieved or decrease when the associated items are out of stock resulting in lost sales therefore a joint inventory policy should be pursued in a cross selling system this paper introduces customer driven cross selling into centralized and competitive newsvendor nv models by representing an item s effective demand as a function of other items order quantities we derive first order optimality conditions for the centralized model in addition to pure strategy nash equilibrium conditions and uniqueness conditions of the equilibria for the competitive model we further develop gradient based gb and iteration based ib algorithms to solve the centralized and competitive models respectively a computational study verifies the effectiveness of the proposed algorithms the computational results show that a larger cross selling effect leads to a larger order quantity in a centralized nv model but a smaller order quantity in a competitive nv model and a larger positive correlation between items demands leads to higher profits with smaller order quantities in both models moreover nvs will order more items if the demand variance is greater however resulting in lower profits in a competitive situation one will prefer smaller order quantities than in a centralized decision situation

inventory management under price based and stockout based substitution abstract we examine a stochastic inventory and pricing problem for a firm that sells two vertically differentiated products the demands for the two products are determined by total random market size and the customers net utility from buying the two products which is determined by the products quality attributes the individual quality valuation unknown to the firm and the selling prices in case the preferred product is out of stock customers may be willing to buy a substitute instead if their net utility is non negative therefore we analyze an inventory and pricing model considering price based and stockout based substitution we show that the demand function is not continuous in price by decomposing the profit function into different price regimes we are able to derive closed form expressions for the stockout based substitution rates upward and downward substitution and the optimal inventory levels under exogenous pricing under endogenous pricing we find that the profit function is not necessarily unimodal however we show that a unique solution exists for the integrated price and inventory problem under price based substitution only numerical results reveal that not considering stockout based substitution i leads to lower profit margins for high quality products and ii may cause severe supply demand mismatches throughout the entire assortment finally we show the performance of two approximated pricing policies

product variety and demand uncertainty why markups vary with quality we demonstrate that demand uncertainty can explain equilibrium product variety in the presence of sunk costs product variety is an efficient response to uncertainty because it reduces the expected costs associated with excess capacity we find that within the firm s product line the highest quality product has the highest profit margin but the lowest percentage margin while the lowest quality product has the highest percentage margin but the lowest absolute margin both of these relationships are consistent with evidence available from marketing studies what determines the breadth of a firm s product line we show that when production costs must be sunk in anticipation of demand demand uncertainty can lead to an increase in product variety by limiting their inventory of high quality goods and selling low quality goods once their high quality goods have stocked out firms reduce the costs associated with demand uncertainty the model helps explain the extent of product differentiation and suggests a rationale for many common retailing practices such as the use of private labels and full product line forcing by manufacturers the model also yields the testable empirical prediction that higher quality products earn higher absolute margins and lower percentage margins while differences in preferences provide a convincing explanation in many cases for product variety in retail stores we argue that another

a classification of the literature on the planning of substitutable products abstract a company s assortment of products and corresponding inventory levels are constrained by available resources such as production capacity storage space and capital to acquire the inventory thus customers may not always be able to find a most preferred product at the time of purchase this unsatisfied demand is often substituted with an alternative in the extant literature there have been an increasing number of studies that consider product substitution when planning product assortment inventory and capacity in conjunction with pricing in this paper we classify the literature on the planning of substitutable products published in the major om and marketing journals during the past thirty years 1974 2013 and present a comprehensive taxonomy of the literature one criterion is adopted to discuss modeling objectives and three major criteria are provided to define the nature of product substitution including substitution mechanism substitution decision maker and direction of substitutability we also identify research gaps to provide guidance for related research in the future

optimizing product assortment under customer driven demand substitution abstract the problem of product assortment and inventory planning under customer driven demand substitution is analyzed and a mathematical model for this problem is provided in this paper realistic issues in a retail context such as supplier selection shelf space constraints and poor quality procurement are also taken into account the performance of three modified models one that neglects customers substitution behavior another that excludes supplier selection decision and one that ignores shelf space limitations are analyzed separately with computational experiments the results of the analysis demonstrate that neglecting customer driven substitution or excluding supplier selection or ignoring shelf space limitations may lead to significantly inefficient assortments the effects of demand variability and substitution cost on optimal assortment and supplier selection decisions as well as on the optimal revenue are also investigated the main contribution of this paper is the development of a practical and flexible model to aid retailers in finding optimal assortments to maximize the expected profit

inventory decisions for substitutable products with stock dependent demand abstract we study a retailer s inventory policy for two products the products are substitutable and have inventory dependent demand so a higher inventory level of a product increases its sales we model the joint effect of demand stimulation and product substitution on inventory decisions by considering a single period stochastic demand setting we provide the first order optimality conditions for the profit maximizing order quantities and interpret them using marginal analysis we also consider two heuristic solutions that separately account for either demand stimulation or product substitution our numerical analysis reveals that the optimal policy by appropriately using sales information that quantifies substitution and demand stimulation can produce significantly higher profits the profit benefits are lessened under certain circumstances such as when the two products have similar critical fractile values suggesting that in such instances the heuristics may be used effectively

social security liquidity and early retirement abstract this paper investigates the effect of social security on retirement decisions it argues that it is important to take realistic account of how recipients evaluate potential benefit flows the paper presents a simple retirement model in which liquidity constraints prompt individuals to use higher than market discount rates in evaluating future pension benefits as a consequence even an apparently actuarially fair early retirement benefit could on average discourage continued work using data on individual retirement decisions i find support for the argument that this phenomenon contributes to some of the observed increase in early retirement

the economics of product variety a survey demand for variety may arise from a taste for diversity in individual consumption and or from diversity in tastes even when each consumer chooses a single variant the full degree of variety potentially demanded will not in general be supplied because scale economies even to a small degree mean that the potential welfare or revenue gain from greater variety must be balanced against the lower unit production costs with fewer variants the economics of product variety consists essentially in analysing the effect of this balance in different situations and comparing the degree of product variety for different market structures with each other and with the optimum the survey commences with the work on market structures with single product firms generalized monopolistic competition tracing modern developments in both the chamberlinian and hotelling traditions the latter has been particularly fruitful due to the expansion of the original locational ideas into virtual spaces in product characteristics the emphasis in recent work on product variety has been on multiproduct firms in both monopolistic and oligopolistic structures including strategic market preemption although most work has been in a full information context there have been advances in product variety under imperfect information either by consumers to properties of the firms products or firms as to consumers demands

optimal production pricing and substitution policies in continuous review production inventory systems abstract we consider the optimal production pricing and substitution policies of a continuous review production inventory system with two products a high end product and a low end product each product has its associated customer stream however the demands for the low end product may be satisfied by the high end product we formulate the problem as a markov decision process and characterize the structure of the optimal control policy which specifies when to produce for each product when to use the high end product as a substitute and how to set the optimal prices we show that a base stock production policy is optimal however the optimal base stock level for each product depends on the inventory level of the other product and it features a monotonic property we also demonstrate that the optimal substitution policy is a rationing policy with the rationing level depending on the total inventory amount we find that the optimal prices can be either decreasing or increasing in the inventory levels depending on the forms of demand functions furthermore we utilize numerical experiments to investigate the impact of different system characteristics on the benefits of using substitution and dynamic pricing finally we investigate when the dynamic pricing strategy and the substitution strategy are complements or substitutes

pricing and operational recourse in coproduction systems coproduction systems in which multiple products are produced simultaneously in a single production run are prevalent in many industries such systems typically produce a random quantity of vertically differentiated products this product hierarchy enables the firm to fill demand for a lower quality product by converting a higher quality product in addition to the challenges presented by random yields and multiple products coproduction systems often serve multiple customer classes that differ in their product valuations furthermore the sizes of these classes are uncertain employing a utility maximizing customer model we investigate the production pricing downconversion and allocation decisions in a two class stochastic demand stochastic yield coproduction system for the single class case we establish that downconversion will not occur if prices are set optimally in contrast we show that downconversion can be optimal in the two class case even if prices are set optimally we consider the benefit of postponing certain operational decisions e g the pricing or allocation rule decisions until after uncertainties are resolved we use the term recourse to denote actions taken after uncertainties have been resolved we find that recourse pricing benefits the firm much more than either downconversion or recourse allocation do implying that recourse demand management is more valuable than recourse supply management special cases of our model include the single class and two class random yield newsvendor models

technical note an expectation maximization method to estimate a rank based choice model of demand we propose an expectation maximization em method to estimate customer preferences for a category of products using only sales transaction and product availability data the demand model combines a general rank based discrete choice model of preferences with a bernoulli process of customer arrivals over time the discrete choice model is defined by a probability mass function pmf on a given set of preference rankings of alternatives including the no purchase alternative each customer is represented by a preference list and when faced with a given choice set is assumed to either purchase the available option that ranks highest in her preference list or not purchase at all if no available product ranks higher than the no purchase alternative we apply the em method to jointly estimate the arrival rate of customers and the pmf of the rank based choice model and show that it leads to a remarkably simple and highly efficient estimation procedure all limit points of the procedure are provably stationa

is german domestic social policy politically controversial this paper investigates empirically the influence of government ideology on social policy using german data examining the funding and the benefits of social security and public healthcare policy my results suggest that policies implemented by governments dominated by left and rightwing parties were similar over the 1951 2007 period leftwing governments however spent more in the 1970s and rightwing governments did so after german reunification in 1990 since policy convergence encourages new parties to enter the political arena and party platforms on social policy matters are likely to undergo further changes in light of demographic change the observed pattern may thus be a transitory phenomenon

population age structure and the size of social security this paper uses a general overlapping generations model to analyze social security rather than focusing on intertemporal price and income considerations however the paper focuses on the effect of contemporaneous same period prices and income the analysis shows that the old age dependency ratio acts as a shadow price for old age benefits with this new shadow price the equilibrium price and quantity of social security benefits and the level of the payroll tax rate are determined in a demand supply framework with individual utility maximization three explicit demand functions intergenerational contracts are analyzed the model is tested using u s time series data for the social security old age and survivors oasi program excerpt

inventory competition under dynamic consumer choice we analyze a model of inventory competition among n firms that provide competing substitutable goods each firm chooses initial inventory levels for their good in a single period newsboy like inventory model customers choose dynamically based on current availability so the inventory levels at one firm affect the demand of all competingfirms this creates a strategic interaction amongthe firms inventory decisions our work extends earlier work on variations of this problem by karjalainen 1992 lippman and mccardle 1997 and parlar 1988 specifically we model demand in a more realistic way as a stochastic sequence of heterogeneous consumers who choose dynamically from amongthe available goods or choose not to purchase based on a utility maximization criterion we also use a sample path analysis so minimal assumptions are imposed on this demand process we characterize the nash equilibrium of the resulting stocking game and prove it is unique in the symmetric case we show there is a bias toward overstocking caused by competition specifically reducing the quantity stocked at any equilibrium of the game increases total system profits and at any joint optimal set of stocking levels each firm has an individual incentive to increase its own stock for the symmetric case we show that as the number of competing firms increases the overstockingbecomes so severe that total system and individual firm profits approach zero finally we propose a stochastic gradient algorithm for computing equilibria and provide several numerical examples

risk coping land tenure and land markets an overview of the literature over the last decades a significant amount of literature has been published on informal risk coping in developing countries in this paper we review how informal risk coping has been addressed in the land tenure literature from two main perspectives a first stream of research looks at how customary tenure and communal property perform key informal risk coping functions a second subset of this literature analyses how informal risk coping creates land market imperfections through sharecropping or distress sales the segmentation of the literature results from the demsetzian property rights framework further research on risk coping and land tenure would benefit from examining recent work on property regimes

public pensions as optimal social contracts abstract a simple overlapping generations model is modified to allow for an externality experienced by the young from consumption by the elderly this sets up a game between generations in which one generation s strategy may be to save too little and rely on gifts from the young e g public assistance for retirement income social security can therefore be viewed as a pareto optimal contract to restore efficient intertemporal allocation a funded public pension plan corresponds to forced saving but is vulnerable in that the next young generation may stop contributing rely on its children for retirement assistance and meanwhile reap the consumption externality from the current elderly s social security benefits this suggests a forced giving or pay as you go type of compulsory pension plan such as exists in most nations which also has the advantage of aiding the initial old generation and therefore generating an immediate consumption externality for the initial young the approach can also be used to explain other aspects of existing social security

the impact of product substitution on retail merchandising abstract we analyze the impact of product substitution on two key aspects of retail merchandising order quantities and expected profits to perform this analysis we extend the basic news vendor model to include the possibility that a product with surplus inventory can be used as a substitute for out of stock products this extension requires a definition and an approximation for the resulting effective demand under substitution a service rate heuristic is developed to solve the extended problem the performance of this heuristic is evaluated using an upper bound generated by solving the associated lagrangian dual problem our analysis suggests that this heuristic provides a tractable and accurate method to determine order quantities and expected profits under substitution we apply this heuristic to examine how the level of demand uncertainty and correlation and the degree of substitution between products affect order quantities and expected profits under substitutable demand in addition we use the heuristic to better understand the mechanism by which substitution improves expected profits

trust networks and norms the creation of social capital in agricultural economies in ghana this paper contributes to the continuing debate over the multifaceted concept of trust and its ability to provide a richer explanation of processes of economic activity using case studies of agricultural production marketing and financing systems in brong ahafo region of ghana the analysis documents the means by which trust is created among farmers traders and agricultural input suppliers the mechanisms include formal and informal networks of working relations customer friendships pre existing networks and intermediaries the study shows that trust is necessary for the development of a vibrant private sector based on microenterprises in conditions where actors cannot rely on formal legal institutions at present

on the relationship between inventory costs and variety benefits in retailassortments consider a category of product variants distinguished by some attribute such as color or flavor a retailer must construct an assortment for the category i e select a subset variants to stock and determine purchase quantities for each offered variant we analyze this problem using a multinomial logit model to describe the consumer choice process and a newsboy model to represent the retailer s inventory cost we show that the optimal assortment has a simple structure and provide insights on how various factors affect the optimal level of assortment variety we also develop a formal definition of the level of fashion in a category using the theory of majorization and examine its implications for category profits

building for the future investment land reform and the contingencies of ownership in contemporary ghana summary case studies of individual investments in tree crops and houses illustrate recent changes in social and economic differentiation among families and communities in asante region ghana and their implications for recent debates over state led land reform versus community led land reform seeking efficiency neoliberal land reforms transfer land from state to private ownership as well as tenure reforms designed to strengthen owners rights by treating communities as owners reforms benefit the poor as well as the well to do in ghana and other west african countries privatization may also work in the opposite direction reinforcing inequalities within communities and encouraging claims to land based on origin and indigeneity

campaign finances and political platforms the economics of political controversy one implication of the widely used median voter model is that candidates have little to gain by disagreement apart from some epsilon of controversy necessary to demonstrate which candidate is closer to the median voter position in the policy dimension in question votes are maximized by taking essentially identical position this is true at the nash median voter equilibrium and is true away from equilibrium as a consequence two candidate competition within one dimensional policy domain is expected to generate considerable agreement about appropriate policy we do in fact observe that in many elections candidate positions converge to very similar positions on matters of broad concern it is largely this convergence that gives the median voter model its considerable credence in spite of the fragility of the underlying theory on the other hand the convergence is rarely as complete as might have been expected and there are elections where candidates take substantively different positions this paper explores the extent to which the campaign contributions of politically active groups may draw candidates away from the median voter position as candidate seek funds to run effective election campaigns candidates gener

state led land reform and local institutional change land titles land markets and tenure security in mexican communities summary this article focuses on the interactions between state and community mechanisms in the design and delivery of a titling program and a land market reform in rural mexico whereas the titling program did provide a greater sense of tenure security among landholders legalizing transactions has unexpectedly generated an informal land market resulting in tenure insecurity for the corresponding buyers these contrasting outcomes are not a matter of technical failure unaffordable fees or rent seeking rather they can be traced back to differentiated processes of policy delivery by the administration officials with regard to acknowledging prevailing local institutions and managing local information

multi period inventory games with information update this paper addresses the multi period inventory game of two substitutable products with learning in which the demand distribution form in each period is known but one or more parameters are unknown in advance the retailers update the estimates of the unknown parameters using the historical demand information as the transaction proceeds at each period the retailers check the initial inventories and update the forecasts about their demands first then they place the orders which are delivered immediately finally the demands are realized and satisfied by the available inventories the unsatisfied demand of one retailer switches to another and is satisfied by the other s left inventory unsatisfied demand is lost and the excess inventories incur a holding cost all the information is common knowledge the objectives of the two retailers are to make proper ordering decisions to maximize their total expected discount profits respectively we model the problem as a dynamic bayesian game with multi dimension state space we give the conditions under which the state space can be reduced we prove the existence and uniqueness of nash equilibrium and show that the equilibrium ordering strategy is the base stock policy the computation of the base stock levels can be reduced to a game with one dimension state space moreover for the case with perishable product the computation of the base stock levels can be reduced to the newsboy game

the making of a rentier class wealth accumulation and political control in senegal political and economic dynamics set in motion by efforts to consolidate post colonial regimes have contributed to the continuing weakness of indigenous bourgeoisies throughout much of post colonial africa this article suggests that state power has been used to foster private rent seeking rather than productive local private investment in order to promote and sustain the political cohesion of ruling classes the political consolidation of dominant rentier classes forged through state patronage and clientelist mechanisms of control creates obstacles to the emergence of local class strata interested in or capable of using state power to promote the expanded accumulation of capital be it local or foreign a study of senegal illustrates this point

assortment planning and inventory decisions under a locational choice model we consider a single period assortment planning and inventory management problem for a retailer using a locational choice model to represent consumer demand we first determine the optimal variety product location and inventory decisions under static substitution and show that the optimal assortment consists of products equally spaced out such that there is no substitution among them regardless of the distribution of consumer preferences the optimal solution can be such that some customers prefer not to buy any product in the assortment and such that the most popular product is not offered we then obtain bounds on profit when customers dynamically substitute using the static substitution for the lower bound and a retailer controlled substitution for the upper bound we thus define two heuristics to solve the problem under dynamic substitution and numerically evaluate their performance this analysis shows the value of modeling dynamic substitution and identifies conditions in which the static substitution solution serves as a good approximation