estimation methods in portfolio selection and the effectiveness of short sales restrictions uk evidence forecasting the mean returns vector and the covariance matrix is a key feature in implementing portfolio theory the performance of the bayes stein method for forecasting these parameters for use in the markowitz model with and without short sales was compared with that of seven other estimation methods and three alternative portfolio selection techniques this paper represents the first large scale empirical investigation of the usefulness of the bayes stein approach using historical data this data was drawn from the london stock exchange in contrast to earlier studies the relative performance of bayes stein was mixed while it produced reasonable estimates of the mean returns vector there were superior methods e g overall mean for estimating the covariance matrix when short sales were permitted when short sales were prohibited actual portfolio performance was clearly improved although there was little to choose between the various estimation methods

an experimental examination of competitor based price matching guarantees we use experimental methods to demonstrate the anti competitive potential of price matching guarantees in both symmetric and asymmetric cost duopolies our findings establish that when costs are symmetric price matching guarantees significantly increase market prices in markets with cost asymmetries guaranteed prices remain high relative to prices without the use of guarantees but the overall ability of price guarantees to act as a collusion facilitating device becomes contingent on the relative cost difference lesser use of guarantees combined with lower average prices and slower convergence to the collusive level suggest that the mere presence of cost asymmetries may curtail collusive behavior

on the competitive effects of price matching policies abstract this paper challenges the conventional wisdom that price matching policies lead to supracompetitive prices by reducing firms incentives to undercut rivals i argue that price matching and price beating policies are more appropriately viewed as a means of price discrimination and develop a model that demonstrates their use as such analysis of this model shows that in contrast to the results of the existing literature price matching and price beating may raise or lower equilibrium prices relative to the equilibrium in which firms may not adopt such policies

information and diversity of analyst opinion this paper examines problems in the use of divergence of analyst opinion as a proxy for estimation risk in empirical studies of security returns and asset pricing models we demonstrate that diversity of opinion can increase even though the amount of private information increases and we show that diversity of opinion may overstate estimation risk if the capital market aggregates the information held by investors we produce empirical results consistent with our conclusions specifically we find that divergence of opinion can produce measures of estimation risk that are inconsistent with a received proxy for estimation risk and with observed common stock returns

on the incidence and variety of low price guarantees abstract this paper provides evidence of the incidence and variety of low price guarantees promises to match or beat a rival s price using data obtained from newspaper advertisements in 37 metropolitan areas in the united states we have a total of 515 low price guarantees in our sample we document their features and we infer firms motives and effects from these features the evidence suggests that the majority of low price guarantees are not consistent with their use as a facilitating device because they tend to apply only to rival firms advertised prices or they are associated with high hassle costs the evidence also suggests that price beating and price matching guarantees differ significantly in their features the former are associated with higher hassle costs apply disproportionately to rival firms advertised prices and are more likely to allow postsale search than are price matching guarantees

output decisions and price matching theory and experiment we study the effects of price matching in a setting in which each firm selects both its price and output simultaneously we show that the availability of a price matching option leads to the cournot outcome in this setting our experimental study confirms this result in the laboratory our finding is a stark contrast to the one obtained in the standard price competition that the most likely market price in the presence of a price matching option is the monopolistic price in addition we show that price matching benefits consumers in markets with a large number of firms if a market has a few firms then the effects of price matching on consumers depend on the market demand and cost functions thus our study suggests that the effect of price matching depends on the strategic variables of the firms data and the online appendix are available at https doi org 10 1287 mnsc 2017 2788 this paper was accepted by eric anderson marketing

short selling and efficient sets the effect of short selling on the composition and location of the efficient set has been analyzed in a variety of ways however the situation typically facing investors where the initial margin requirement is less than 100 percent and the riskfree interest rate that is paid on the short proceeds is less than the rate paid on initial margin has not previously been considered the elton gruber padberg algorithm 1976 1978 subject to certain modifications is shown here to be capable of identifying the efflcient set under such conditions when harry markowitz 1952 developed the notion of efficient sets as a method of identifying an investor s optimal portfolio he did so in a setting where short selling was prohibited since then the effect of short selling on the composition and location of the efficient set has been considered in a variety of ways for example lintner 1965 suggested that short sales be treated from the perspective of a broker dealer where an amount of money equal to the short proceeds must be put up as initial margin with the short seller receiving riskfree interest on both the short proceeds and the margin alternatively black 1972 and merton 1972 assumed that the short seller did not have to put up any initial margin and that the short seller actually got the use of the short proceeds more recently dyl 1975 has assumed that the short seller must put up initial margin that is less than the short proceeds but receives no interest on either the margin or short proceeds this paper is concerned with the generation of efficient sets where short selling is allowed but with certain restrictions attached to it referred to hereafter as restricted short selling in particular initial margin is required but can be met by depositing interest bearing securities with the brokerage firm where the short seller s account is kept furthermore the model allows the short seller to earn interest on the short proceeds accordingly the model

competitive price matching guarantees equilibrium analysis of the availability verification clause under demand uncertainty price matching guarantees involve a retailer matching the lower price of a competitor for an identical product in reality retailers often make such guarantees contingent on the verification of product availability at the competitor s location and decline a price match request if the product is not available there this creates certain consternation on the part of customers in this paper we investigate the availability contingency strategy from the perspectives of both the retailers and the customers our analysis shows that availability contingency clauses intensify inventory competition between retailers and reinstitutes price competition which is otherwise eliminated by unconditional price matching guarantees consequently despite what customers may think about the availability verification it actually increases their surplus on the other hand such a clause reduces profits and hence is not the equilibrium strategy for retailers subsequently we discuss how a likely customer behaviour pattern may be a plausible explanation regarding the use of the clause by the retailers in practice this paper was accepted by yossi aviv operations management

estimation risk and simple rules for optimal portfolio selection elton gruber and padberg egp 6 7 have recently simplified the process of constructing optimal portfolios by developing simple criteria for optimal portfolio selection which do not involve use of mathematical programming their simple decision rules permit one to determine easily which securities to include in an optimal portfolio and how much to invest in each however in practical applications of theoretical models sample estimators are usually treated as if they were true values of unknown parameters as a result the effect of the standard errors of sample estimators on decision rules are completely ignored bawa brown and klein 1 have shown that what is optimal in the absence of estimation risk is not necessarily optimal or even approximately optimal in the presence of estimation risk moreover brown 4 examined optimal portfolio choice under uncertainty for various portfolio selection procedures the diffuse bayes rule the markowitz certainty equivalent ce rule the aggregation ce rule and the equal weight rule 1 and found that the diffuse bayes rule uniformly dominates the markowitz ce rule in repeated samples for the quadratic utility case as the sample size increases the bayes rule becomes superior to the aggregation ce and the equal weight rules in addition the result holds even where the probability distribution of returns is seriously misspecified thus brown s 4 study has clearly indicated that without taking estimation risk into account portfolio selection rules other than the bayes rule can lead investors to select suboptimal portfolios this paper shows by using the single index model for the return generating process that the simple decision rules for optimal portfolio selection derived by elton gruber and padberg 7 are not identical under the bayesian and the traditional methods of analysis 2 moreover in the case where short sales are not

effective price matching a comment abstract corts economic lett 47 1995 417 showed that when allowing for price beating policies in addition to price matching policies the competitive outcome prevails in lieu of monopoly pricing i show by expanding the strategy set further to include effective price strategies the possibility of monopoly pricing is restored

on the use of low price guarantees to discourage price cutting abstract this paper formulates a novel test to assess whether and to what extent firms might be using low price guarantees to discourage their rivals from cutting prices the test is based on a comparison of paired observations of advertised prices that are set by competing firms at the same point in time on similar items where one price is set by a firm that has a low price guarantee and the other by a firm that does not have a low price guarantee using data on retail tire prices we find that the majority of paired observations involving firms that have price matching guarantees are consistent with what one would expect if firms were using them to discourage price cutting whereas the majority of paired observations involving firms that have price beating guarantees are not this suggests that price matching and price beating guarantees may be serving different purposes the evidence also suggests that guarantees that apply to advertised prices only may be serving different purposes than guarantees that apply to both advertised and selling prices

experimental duopolies under price guarantees in a symmetric differentiated experimental duopoly we test the ability of price guarantees pgs to raise prices above the competitive levels different types of pgs aggressive and soft price beating and price matching are implemented either as an exogenously imposed market rule or as a business strategy our results show that pgs may lead close to the collusive outcome depending on whether the interaction between duopolists is repeated and provided that the guarantee is not of the aggressive price beating type

matching own prices rivals prices or both many retailers promise that they will not be undersold by rivals and extend their promise to include their own future prices that is many retailers combine elements of both price matching guarantees and retroactive most favored customer clauses this is puzzling because the extant literature has shown that each practice independently has the potential to facilitate supracompetitive prices and thus one might think the two practices are substitutes in this paper we show that price matching guarantees and most favored customer clauses complement each other when offered unilaterally by a single firm and can lead to higher prices than either one could have facilitated by itself

on the robustness of the argument that price matching is anti competitive abstract the existing literature suggests that price matching leads to monopoly prices i show that this argument relies on an arbitrary and unrealistic restriction of the firms strategies in particular if firms may adopt price beating policies the competitive outcome prevails

price matching guarantees and consumer search abstract this paper examines the effect of price matching guarantees pmgs on market outcomes in a sequential search model pmgs are simultaneously chosen with prices and some consumers shoppers know the firms decisions before buying while others non shoppers enter a shop before observing the price and whether or not the firm has a pmg in such an environment pmgs increase the value of buying the good and therefore increase consumers reservation prices this increase is so large that even after accounting for the possible execution of pmgs firms profits are larger in an equilibrium where pmgs are offered than in an equilibrium without pmgs we also consider the incentives of firms to choose pmgs and show that an equilibrium where all firms offer pmgs does not exist because of a free riding problem

research note price matching guarantees retail competition and product line assortment price matching guarantees pmgs are offers to match a competitor s price on a specific item such guarantees are extremely common in u s retail practice and their impact has been studied in several published papers the existing analytic literature models each retailer as a single product seller most work assumes that each retailer s product is identical with or completely substitutable for the competitor s product in reality competing retailers often sell multiple products and these products do not always overlap or may overlap partially but not totally furthermore retailers that offer pmgs routinely exclude certain offerings from pmg coverage this raises the interesting question of how product variety and product stocking factors affect retailer decisions about offering pmgs in this paper we simultaneously consider three factors of retailing importance that imply results consistent with pmg use and nonuse the ability to choose to stock the same product as or a product differentiated from a competitor s offering the possibility of shelf space limitations on the ability to stock complete variety and the category demand enhancing effect of variety these are sensible and realistic descriptive factors shaping retailers product and pricing decisions and because they have not been considered jointly in the prior literature on pmgs their joint consideration helps to expand our understanding of the drivers of pmg implementation and impact in the presence of these three factors we examine retailers decisions about whether to offer a pmg what product s to stock and how to price the product s stocked our results show that shelf space limitations have an important influence on pmg provision in particular when retailers are shelf space constrained and product substitutability in the category is sufficiently large choosing to use pmgs which by definition also requires stocking identical products is strictly less profitable than enduring bertrand price competition but enjoying retail product differentiation the result that pmgs can be profit reducing relative to head to head retail competition is a novel one driven in our model by the opportunity costs of stocking identical products i e the inability to benefit from the demand enhancing effects of variety and the differential small or large between bertrand pricing and pmg pricing levels we further show that under asymmetric shelf space availability either product variety will be severely limited or retailers will offer a different array of products weak substitution between products leads to the latter with pricing between the differentiated products bertrand and monopoly levels strong substitution leads to the former with pricing at the monopoly level our results also show that with unlimited shelf space both competing retailers offer pmgs stock the entire available product line and enjoy monopoly pricing given our focus on product variety issues we also relate our results to the literature on branded variants our results demonstrate that the nature of product variety the availability of retail shelf space and the category demand enhancing effect of variety are key market characteristics that jointly and strongly affect the optimality of pmgs and the resulting pricing and profitability characteristics of the market

do low price guarantees guarantee low prices evidence from competition between amazon and big box stores it has long been understood in theory that price match guarantees can be anticompetitive but to date scant empirical evidence is available outside of some narrow markets this paper broadens the scope of empirical analysis studying a wide range of products sold on a national online market using an algorithm that extracts data from charts i obtain a novel source of data from online price trackers i examine prices of goods sold on amazon before and after two big box stores target and best buy announced a guarantee to match amazon s prices employing both difference in difference and regression discontinuity approaches i robustly estimate a positive causal effect of six percentage points the effect was heterogeneous with larger price increases for initially lower priced items my results support anticompetitive theories which predict price increases for amazon a firm that did not adopt the guarantee and are consistent with plausible mechanisms for the heterogeneous impact

policy responsiveness and incumbent reelection in state legislatures does policy responsiveness on the part of incumbent legislators affect their prospects for reelection recent studies of congressional campaigns demonstrate that incumbents who support policies that are more congruent with their constituents preferences face fewer reelection obstacles the present analysis considers this question in state legislative elections where voter knowledge of legislator activities is generally quite low the findings demonstrate that incumbents positioned farther from the average citizen and toward their party s base are only slightly more likely to be challenged than other incumbents however more partisan voting incumbents do attract challengers capable of raising and spending larger amounts of money interestingly incumbents positioned closer to their party s base actually receive a greater share of the vote in most contested elections only when challengers spend significant amounts of money do we see the positive effects of partisan voting by incumbents diminished overall these findings demonstrate the mechanisms by which policy positions of incumbents in a low information environment affect the challengers that emerge and the level of voter support received

research note consumer heterogeneity and competitive price matching guarantees price matching guarantees are widely used in consumer and industrial markets previous studies argue that they are a marketing tactic that facilitates implicit price collusion this is because once a store adopts this marketing tactic its rivals can no longer steal its customers by undercutting its price and hence they have little incentive to initiate price cuts while a store with price matching guarantees has no fear of losing customers to rivals price cuts it has every incentive to raise its own price to charge a higher price to its loyal consumers a growing body of legal literature uses this argument today to justify calls for antitrust actions against stores employing this marketing tactic however this theoretical conclusion baffles practitioners and industry experts in practice sellers typically embrace this marketing tactic in response to heavier competition and a growing bargain consciousness among shoppers the introduction of price matching guarantees by a store is frequently interpreted by industry observers as the initiation of a price war rather than a signal of price collusion this assertion is supported in many instances by the fact that stores that introduce price matching guarantees also roll back their prices and typically suffer subsequent loss of profits most ironically the favorite examples used by researchers to illustrate how price matching guarantees can enforce price collusion crazy eddie and nobody beats the wiz have subsequently either gone bankrupt or filed for federal bankruptcy protection in this study we show that price matching guarantees can indeed facilitate competition the expected prices and profits can be strictly lower when all stores adopt price matching guarantees than when they are not allowed to this is because the adoption of price matching guarantees generates not only a competition dampening effect which has been recognized in the literature but also a competition enhancing effect this latter effect comes from the fact that price matching guarantees encourage price search by those consumers who prefer to shop at a particular store but are mindful of saving opportunities these consumers will have incentives to obtain the rival store s price when their favorite store offers price matching guarantees to avail themselves of the lowest possible price at their favorite store as a result price matching guarantees reduce the number of purchases at the store from those consumers who would have paid the full price and thus prompt a store to price more aggressively to bid for more incremental sales this competition enhancing effect can more than offset the competition dampening effect in markets where consumers differ in their price search costs and store loyalty thus our study casts doubt on the advisability of blanket prohibition on price matching guarantees our argument relies only on consumer segmentation and on the phenomenon of periodic sales both of which are common in retail markets we arrive at our conclusion by incorporating bargain shoppers and opportunistic loyals into the standard sales promotion models in contrast the past literature on price matching guarantees ignores the ubiquitous phenomenon of sales in retail markets and overlooks those consumers who prefer to shop at a particular store but are alert to saving opportunities as a result it is troubled by two awkward conclusions on the one hand price matching guarantees simply remove rivals incentives to undercut in price and hence also their incentives to run sales this implies that the adoption of price matching guarantees in a market will eliminate the phenomenon of sales which is obviously counterfactual on the other hand in equilibrium no consumer actually invokes price matching guarantees as each player has incentives to close any price gap in the market this is obviously false based on our casual observations and our conversations with store managers theoretical research on the subject thus far has been overwhelmingly one sided and empirical or experimental studies are conspicuously lacking we hope that our conclusion will spark further research in both directions a healthy debate will broaden our perspective on an issue of great importance in formulating public policies and in managerial decision making

platform monopolization by narrow ppc bpg combination booking et al abstract the price parity clauses ppcs that online booking platforms impose have come under antitrust scrutiny wang and wright 2017 show how by preventing showrooming a narrow ppc can reduce search costs and benefit consumers under between platform competition in response to having to give up its wide ppc to hotels booking com emphasized its best price guarantee bpg to customers we observe that a narrow ppc combined with a low hassle costs bpg leaves only wang and wright s price parity and monopoly equilibrium ppme in which consumers are worse off than with no platform operating at all a more efficient incumbent platform can deter entry with the bpg while the narrow ppc eliminates competition from direct sales channels an equally efficient platform could enter and compete consumer prices down because of the existence of hassle costs yet this equilibrium is fragile to network effects if sellers have incentives not to price differentiate between platform s and their direct sales channel a narrow ppc alone suffices to sustain the ppme in both cases the detrimental pricing contract combination that we point out calls for different platform competition policy