Pricing decision models for a two-echelon supply chain with stochastic price-dependent demand Tian Zhiyu Supervisor: Xu Chen Pan Jingming Abstract: In this paper we study the impact of power structure, information and demand fluctuation on the pricing decision of supplier and retailer in a two-echelon supply chain. We first develop and analysis the case that supplier as the leader in the symmetric information scenario and consider the way to improve the supply chain performance. Then we discuss the impact of asymmetric information on pricing decision. We also explore the impact of power structure on the pricing decision. A series of characters and principles are drawn. Keywords: Supply chain, Stochastic price-dependent demand, Pricing decision, Game 1 Introduction Typically in the literature on supply chain coordination, the decisions are set by a central decision-maker to optimize total supply chain profit[1][2][3]. This centralized approach requests all members’ interest to be consistent, or despite the conflict of interest, the central decision-maker can control the system and other members submit to the system interest optimization. Since most supply chain systems are decentralized, the centralized approach ignored the competition of the supply chain members. Competitive behavior between members may lower the supply chain efficiency, so the centralized optimization approach is only an approximation of the real supply chain system and the massiness and stability is irresponsible. Most of the studies of the decentralized supply chain have been focused on the design of all members’ sub-goals or performance measurement schemes to mitigate the incentives problems of all members in the supply chain[4][5][6]. In these literatures market parameters such as demand and selling price are exogenous. However, take these factors into consideration can provide an excellent vehicle for examining how operational problems interact with marketing issues to influence decision making at The anthor: Tian Zhiyu, an undergraduate of School of Management, University of Electronic Science and Technology. the firm level. We use the following two-echelon gaming structure: a supplier wholesales a product to a retailer, who in turn retails it to the consumer. The retail market demand is price-dependent and stochastic. How should the supplier and retailer make their pricing and batch-size decisions? The purpose of this paper is to analyze this problem. 2 Literature Review There have substantial studies that range from marketing to operations research and management on the pricing problems. The marketing literature often focuses on the coordination of pricing decisions in a single period, without production and inventory considerations. The operations literature, on the other hand, has traditionally been focused on coordinating production and inventory decisions, assuming that price and demand are given. Elmaghraby and Keskinocak[7]give an extensive literature review of this literature. Now we will concentrate on those that are related to our study. The pricing model of the decentralized supply chains has been first studied under Stackelberg game framework by Eliashberg and Steinberg[8]. The major concern in their study is to characterize properties of the pricing and production policies of the Stackelberg solution. Then many studies focused on this problem for a two-echelon supply chain channel[9][10][11][12]. Their study is based on the assumption that the price-dependent demand curve is deterministic, either liner or iso-elastic. Lau and Lau[13]showed that the demand-curve’s shape can affect the system’s optimal solution in some very counter-intuitive ways, thus demonstrating that results derived from assuming one demand-curve shape cannot be safely generalized to other demand curve shapes. Considering the stochastic and price-dependent demand and the product’s savage and opportunity value, Whitin[14], Mills[15], Porteus[16] and Zabel[17] formulated a newsboy model with stochastic price-dependent demand. This parallels in many ways the observation that since the 1950s, the practice of operations has emphasized functional efficiency at the expense of cross-functional effectiveness. Comparing with the above studies, our work has three main differences. First, the demand function is stochastic and price-dependent demand. The objective function is a utility function. Second, we discuss the impact of asymmetric information on the decision of the more powerful supplier. Third, the impact of power on the pricing decision is studied. 3 Basic Definitions and Assumptions Denotation definition: c-unit manufacturing cost; w-unit wholesale price; p- unit retail price; q-quantity that the retailer orders; D-market demand. We assume market demand for the product D is stochastic price-dependent as D(p,ε)=a-bp+ε (a>0, b>0 and p∈(0,a/b))[15], where a-bp is a decreasing function of p that captures the dependency between demand and price, and b is the demand elasticity in respect to retail price, ε is a random variable with known distribution that shows randomness in demand and is price-independent, we assume that ε follows Normal distribution with mean μ=0 and standard variance σ, i.e., ε~N(0, σ2). In order to assure positive demand in some rang of p, we require that a>σ. Obviously D(p,ε) is also Normal distribution with mean μD= a-bp and standard variance σD=σ. On the basis of above and with some common sense, we can educe p>w>c and a>bw>bc. In addition, the supplier and retailer each has a reservation profit, and they will not participate in the channel if their expected profit are less than that. We assume it is zero for each, so they will choose to participate in the supply chain channel on condition that their expected profits are non-negative. 4 Model Formulation and Analysis 4.1 Symmetric information supplier-Stg game In this section, we assume that the supplier is a Stackelberg leader and the retailer is a Stackelberg follower (hereafter the “supplier-Stg” game) and information is symmetric. This relationship between the supplier and retailer is a sequential noncooperative game. The process can be explained as follows. The supplier as the leader first declares the wholesale price and the retailer as the follower then decides on the retail price and quantity of products to order. The supplier maximizes its profit by specifying the optimal wholesale price taking the behavior of the retailer into account. The retailer’s decision is setting the optimal retail price to maximize its profit at given wholesale price. The solution of this game is called Stackelberg equilibrium. 4.1.1. The retailer’s problem We first study the retailer’s problem. As a Stackelberg follower, the retailer’s problem is to find optimal retail price p, given the wholesale price w. His profit function is πr=(p-w)D(p,ε), clearly it is a Normal distribution with mean μπ=(p-w)(a-bp) and standard variance σπ=(p-w)σ. So the retailer should consider the trade-off between the expected revenue and the revenue’s standard deviation in taking a decision[18]. To explicitly effect this trade-off, we propose to define a utility function Uπr(p) as the retailer’s objective (as Cheng, 1984) [19]: Uπr(p)=μπ-λσπ where λ is the mean and standard deviation trade-off factor specified by retailer. The retailer’s problem is to optimal the retail price at the given wholesale price to maximizing the utility function, that is: max U r p p w a bp . p Hence, Uπr(p) is concave with respect to p where p∈(w,a/b) and there exists a unique optimal retail price at given wholesale price w to make the retailer’s utility function maximization. Setting ∂Uπr(p)/∂p=0, we get the optimal retail price, which is a function of wholesale price: p(w)=(a+bw-λσ)/2b where w∈(c,(a-λσ)/b). Substituting it into q(p)=a-bp-λσ, we can obtain the retailer’s optimal order quantity q(w)=(a-bw-λσ)/2. 4.1.2 The supplier’s problem The supplier has dominant bargaining power with symmetric-information in this supplier-Stg game, and can correctly anticipate the retailer’s reacting for any wholesale price and select optimal wholesale price which maximizes his profit. The supplier faces demand curve q(w) and chooses w to maximize his expected profit: Eπs=(w-c)q(w). We also introduce a utility function Uπs= Eπs(w) as the supplier’s objective, i.e., Uπs= (w-c)(a-bw-λσ)/2. Since Uπs is concave with respect to w where w∈(c,a/b), Hence, the supplier’s utility function is concave with respect to wholesale price, and there exists a unique optimal wholesale price to make the supplier’s utility function maximization. Setting ∂Uπs(p)/∂w=0, we get the optimal wholesale price w* =(a+bc-λσ)/2b. Substituting it in to the above equation, we get the optimal retail price p* =(3a+bc-3λσ)/4b and the optimal ordering quantity q* =(a-bc-λσ)/4. (w*,p*) is the Stackelberg equilibrium. Then the retailer, the supplier and the channel’s utilities are, respectively: Uπs*=(a-bc-λσ)2/8b, Uπr*=(a-bc-λσ)2/16b, Uπ* =Uπs*+ Uπr*=3(a-bc-λσ)2/16b. Proposition 1: (1) The optimal wholesale price is decreasing in b, the optimal retail price is decreasing in b. (2) The optimal wholesale price is decreasing in σ, the optimal retail price is decreasing in σ. (3) The division of channel utility between the supplier and retailer, i.e., the ratio of maximal utility, RU=Uπs*/ Uπr*=2. 4.1.3 The integrated benchmark To establish a performance benchmark, we study the problem of an integrated firm, this is the instance that the supplier and retailer choose the strategy of cooperation and their objective is to maximize the channel’ profit. Consider first what an integrated firm would do, it will choose optimal retail price to maximize the channel’ profit. The integrated channel profit πi=(p-c)D(p,ε) is a Normal distribution, i.e., πi ~N((p-c)(a-bp),(p-c)2σ2). Consider the trade-off between the expected profit and the profit’s standard deviation in taking a decision and assume the trade-off factor between the mean and standard deviation specified by the integrated firm is the same as the retailer’s, we define a utility function Uπi(p) as the integrated firm’s objective: max U i p p c a bp p c . p Thus, Uπi(p) is concave with respect to p where p∈(c,a/b). We get the integrated firm’s optimal retail price pi*=(a+bc-λσ)/2b and maximal utility Uπi*(p)= (a-bc-λσ)2/4b. We define channel efficiency as CE=Uπ*/Uπi* to describe the channel performance. Thus, CE of supplier-Stg game is 0.75. Proposition 2: (1) The integrated firm’s maximal utility is decreasing in σ. (2) The integrated firm’s optimal retail price is lower than the supplier-Stg channel’s. Conclusion 1: (1) The wholesale price and retail price both are decreasing in price elasticity of demand, i.e., the lower the price elasticity of demand, the higher the wholesale price and retail price. This is accord with the pricing principle in microeconomics. (2) Taking the demand fluctuation into consideration, the supplier and retailer both will set lower price to deal with the uncertainty. The retailer will order fewer products with more fluctuating demand. The supplier’s and retailer’s utility at the Stackelberg equilibrium strategy are decreasing in the standard deviation of demand. (3) As the Stackelberg leader, the supplier’s utility is two times as the retailer’s. So the leader position is an advantage to gain more utility than the follower position for the supplier in the symmetric information scenario. (4) The integrated firm’s optimal retail price is lower than the supplier-Stg channel’s. (5) The supplier-Stg channel’s efficiency: CE 0.75 . 4.1.4 How to improve the channel performance We have learn that the supplier and retailer can improve channel performance by cooperation, but the supplier and retailer will choose cooperation only when cooperation will not decrease each other’s profit. Now we study how to negotiate the wholesale price and the split of channel profit. Let p=(1+r)w, (1+r) is the retailer’s markup ratio, so we get the integrated firm’s objective: max U i w, r 1 r w c a b 1 r w w, r i Hence, Uπ (w,r) is concave with respect to (w,r), where w∈(c,a/b) and r∈(0,(a-bc)/2bc). Hence there exists a unique optimal strategy set (wpe,rpe) to make the utility function maximization. Solving it we get the optimal strategy set:Z={((wpe,rpe))| rpe=(a+bc-λσ)/2wpe-1, wpe∈(c,a/b), rpe∈(0,(a-2b)/2bc)}. Proposition 3: The integrated firm’s optimal strategy is Pareto efficient strategy and there exits feasible Pareto efficient strategy: {((wfpe,pfpe))|(a+3bc-λσ)/4b<wfpe<(3a+5bc-3λσ)/8b,pfpe=(a+bc-λσ)/2b} that can improve the supplier and retailer’s condition synchronously. Thus the retailer and supplier can choose to cooperation at the set (wfpe,pfpe) to improve the channel performance, and the supplier’s profit is increasing in wholesale price and the retailer’s profit is decreasing in wholesale price, so the wholesale price is determined by the players’ bargain power, attitude toward risk, i.e. trade-off factor and so on. Then we assume the channel utility split factor is α(0<α<1), then Uπis*=αUπi*>Uπs* and Uπir*=(1-α)Uπi*>Uπr*. Thus, we obtain the optimal wholesale price wfpe*=(2bc+α(a-bc-λσ))/2b at 0.5<α<0.75. And we can get ratio of utility 1<RUi<3. This is the condition that the supplier and retailer will choose cooperation to improve the channel efficiency. 4.2 Asymmetric information Supplier-Stg Game We assumed that the supplier is the powerful player, the market demand is stochastic and price-dependent and information is symmetric, on this scenario the supplier knows the retailer utility function, i.e., the price dependent demand a-bp, the retailer’s trade-off factor between the mean and standard deviation λ and the market demand’s standard deviation σ, so we get the exact deterministic Stackelberg equilibrium (w*,p*). At this equilibrium, RU=2 and CE=0.75. The integrated firm shows that 1<RUi<3 and CE=1. It seems that the supplier’s leading position ensures him more power consequently much more profit than the retailer. Such result is based on the symmetric information and stochastic scenario. This model has omitted the factor that in the stochastic environment information can hardly be symmetric. The retailer as the downstream partner facing the market demand directly and has more precise information of the fluctuation of demand than the supplier as the upstream firm. Consider now information asymmetric and stochastic scenario. The factor σ are known to be a constant, but the value is uncertain to the supplier at the time when he has to set w, i.e., the supplier perceives D(p,ε) as D(p,ε)~N(a-bp, õ2), where õ is a random variable. In contrast, we assume that the retailer can wait until the actual σ-value is known before ordering, and that the supplier is aware of this. It appears reasonable to assume that the supplier might consider the following arrangements: (Ⅰ)Enforce the same actions that an integrated firm would take. This requires pre-negotiating a percentage to split of channel profit, then the retailer and the supplier cooperation to set the optimal retail price to maximize the channel profit after the actual σ-value is known to the retailer. (Ⅱ)Enforce a supplier-imposed retail price before knowing the actual σ-value. (Ⅲ)Play the supplier-Stg game, i.e., the supplier sets only w, and leave the retail pricing decision entirely to the retailer. 4.2.1 Alternative (Ⅰ) the integrated firm Consider first what an integrated firm would do. The firm knows that after observing the actual value of σ, it can choose optimal retail price to maximize the channel’s utility. This scenario is the same as the integrated benchmark, so the optimal retail price and the maximal utility are, respectively: pI*=pi*=(a+bc-λσ)/2b, UπI*(p)=Uπi*(p)= (a-bc-λσ)2/4b. Now we consider the actual situation in which the supplier and retailer are separate entities. Assume that the players have agreed through solving the problem of how the retail price is set that the supplier should receive α(0<α<1) of the channel’s profit. Coordination can theoretically be done as follows: the supplier asks the retailer to set p at whatever level necessary to maximize channel utility after σ is revealed to the retailer. The supplier will then charge the retailer w that is pre-negotiated or will lead to the pre-negotiated percentage split of channel profit. In the integrated benchmark, the supplier and retailer will choose cooperation when they will obtain more utility than they play the supplier-Stg game. But in this arrangement, the supplier faces asymmetric-information and retailer has more market demand information, i.e., the retailer has more negotiation power on the utility split now. In the information asymmetric scenario, w and α is also determined by the players’ bargain power, attitude toward risk, i.e. trade-off factor λ in our model and so on. But the difference is at first the supplier have to charge initial shipments to the retailer, it maybe higher or lower than the optimal w; then after σ is determined by the retailer and the final total retail revenue is realized, the supplier refunds the retailer the amount UπIs*-αUπI* (the higher w arrangement) or the retailer remits to the supplier a supplementary payment UπIr*-(1-α)UπI* (the lower w arrangement). Both arrangements require one player to trust that the other would reimburse an appropriate amount at the end of the selling activity. Although there is no theoretical reason why this is impossible, it does imply a much higher level of willingness to coordination and share information than in the symmetric information situation, there is now a genuine inconvenience in replicating the integrated firm. 4.2.2 Alternative (Ⅱ) supplier-imposed retail price In this arrangement, we assume the supplier impose a retail price ps before knowing the actual σ value. For any realized σ value, the quantity the retailer will order is q=a-bps-λσ. So the supplier’s utility:UπIIs=(w-c)(a-bps-λõ). Hence the utility is stochastic and the supplier’s expected utility: EUπIIs= (w-c)(a-bps-λEõ). So the supplier will set the wholesale price as high as possible and the retail price as low as possible as soon as the retailer’s expected utility is above retailer’s subsistence level θ. Thus the supplier’s objective is: max EUs ps c a bps Eo . ps Following the way above, we can obtain ps*=(a+bc-λEσ)/2b. After observation the actual σ value, the retailer will order (a-bc+λ(Eσ-2σ))/2 unit products, so the channel’s utility is: UπII*=(a-bc-λEσ) (a-bc+λ(Eσ-2σ))/4b. 4.2.3 Alternative (Ⅲ) play the supplier-Stg game We now assume that before observing the actual σ value, the supplier sets optimal w that maximizes his expected utility, knowing that after being informed of w, the retailer will set p after observing both w and the actual σ. The supplier knows that for any given w and observed σ, the retailer will set p(w,õ)=(a+bw-λõ)/2b and thus q(w,õ)=(a-bw-λõ)/2. So the supplier’s objective is: max EUs w c a bw E 2 . w Hence, we obtain: pIII*=(3a+bc-λ(Eσ+2σ))/4b, wIII*=(a+bc-λEσ)/2b UπIIIs*=(a-bc-λEσ)(a-bc+ λ(Eσ-2σ)) /8b, UπIIIr*=(a-bc+λ(Eσ-2σ))2/16b, UπIII*=(3a-3bc-λ(Eσ+2σ))(a-bc+λ(Eσ-2σ))/16b. Conclusion 2: (1) Alternative(Ⅰ) yields the highest expected total channel utility, but it is also the most unrealistic. (2) Alternative(Ⅱ)’s maximal utility is concave with respect to Eσ, and it reaches maximal point where the Eσ=σ, i.e., the supplier estimate the σ-value precisely. At this maximal point, the channel’s utility is the same as the Alternative(Ⅰ)’s. Alternative(Ⅲ)’s maximal utility is increasing in Eσ. This can be explained as follows: a higher Eσ implies a lower w and p but a higher retailer’s marginal profit and a higher ordering quantity. Thus, a higher channel utility can be realized whereas the division of channel utility between the supplier and retailer decrease. (3) The difference between Alternative(Ⅱ) and Alternative(Ⅲ)’s maximal utility is concave with respect to Eσ. Generally, Alternative(Ⅱ)’s utility is larger than Alternative(Ⅲ)’s where Eσ<(a-bc+2λσ)/3λ and Alternative(Ⅱ)’s utility is smaller than Alternative(Ⅲ)’s where Eσ>(a-bc+2λσ)/3λ. That is to say, the lower supplier’s estimated standard variance of demand implies more advantageous of Alternative(Ⅱ) than Alternative(Ⅲ) and the higher standard variance of demand implies more advantageous of Alternative(Ⅲ) than Alternative(Ⅱ). Exceptionally, in the condition that σ>(a-bc)/2λ and -(a-bc-2λσ)/λ>Eσ>0, Alternative(Ⅱ)’s utility is smaller than Alternative(Ⅲ)’s. This is the condition that the standard variance of demand is sufficiently large, the lower supplier’s estimated standard variance of demand will make Alternative(Ⅲ) performance better. (4) At Alternative (Ⅲ), the supplier choose to play supplier-Stg game and the supplier’s utility is smaller than the retailer’ utility in condition that Eσ>(a-bc+2λσ)/3λ in the general condition, and -(a-bc-2λσ)/λ>Eσ>0 in the exceptional condition that σ>(a-bc)/2λ. In these conditions that the standard variance of demand is small and the supplier’s estimated standard variance of demand is large or the standard variance of demand is sufficiently large and the supplier’s estimated standard variance of demand is small, the more power supplier’s utility is less than the weaker retailer’s. So on the asymmetric information and stochastic scenario the supplier-Stg game often require the more powerful player to either accept much lower profits than the weaker counterpart or be able to compel the weaker party to participate at other arrangements. 5 A More Powerful Retailer In the literature of OR/MS supply chain coordination, the focus is on a relationship in which supplier is the leader and retailer is the follower. This implies the dominant power of supplier over retailer. Recent market structure reviews have shown a shift of power from supplier to retailer. Based on this market phenomenon, in this section we study two conditions that the retailer has more power: retailer as the leader (hereafter the retailer-Stg game) and the retailer and supplier have equal power. 5.1 The retailer as Stackelberg leader We first study the retailer-Stg game. The retailer takes an active role and declares a nonnegative marginal profit v so the retail price is p=w+v. The supplier reacts by choosing w that maximizes his utility given the declared value v. The retailer has complete knowledge of the reaction w, so he can choose the optimal value of v to maximize his profit. We assume the supplier has the same attitude toward risk as the retailer, i.e. trade-off factor λs=λ. We also define the supplier and retailer’s objectives are, respectively: Uπs(w)=(w-c)(a-b(w+v)-λσ) and Uπr(w)=v(a-b(w(v)+v)-λσ). Following exactly the same approach we obtain: w** =(a+3bc-λσ)/4b , p** =(3a+bc-3λσ)/4b. The channel efficiency CE=0.75 and the division of channel utility between the supplier and retailer RU=1/2, i.e., this is similar to the supplier-Stg game. In the retailer-Stg game, the leader retailer declares that he will have a unit profit margin (or markup) of v, regardless of what the supplier does. It is not self-evident that the retailer can be the leader, so imposing this game would require justification. 5.2 The equal power scenario Now we study the case he retailer and the supplier have equal power and make their decision of retail price and wholesale price simultaneously and non-cooperatively maximize their profit with respect to any possible strategies set by other member in the system. This problem is a simultaneous move game and the solution is called Nash equilibrium. In this game, we assume the retailer make the decision of a markup ratio of price (1+r) and at the same time the supplier make the decision of w. We also define the supplier’s objective as Uπs(w)= (w-c)(a-b(1+r)w-λσ) and the retailer’s decision function is p(w)=(a+bw-λσ)/2b as section 4.1.4. Following exactly the same approach we get the Nash equilibrium (w***, p***): 4b , 8bc a b c 8b . w*** bc 8bc a b 2 c 2 p*** 4 a bc 2 2 Conclusion 3: (1) From section 4.1, 5.1 and 5.2, we can educe w***<w*, w**<w*, Uπs***<Uπs*, Uπs**<Uπs*. Hence, the supplier can set higher w and obtain more utility as the leader. It is more complicated in the compare of the follower and equal power position. w***>w* where a≥3bc, (a-3bc)/λ<σ<(a-bc)/λ or bc a 3bc and at this condition Uπs**<Uπs***. This is the general condition that the supplier set higher wholesale price and obtain more utility with more power. Considering the standard variance of demand, the exceptional condition is w***<w** where a>3bc, 0<σ<(a-3bc)/λ and at this condition Uπs**>Uπs*** where a>(7+5×20.5)bc, 0<σ<(a-(7+5×20.5)bc)/λ. With the growing market size and the small fluctuate of demand, the retailer’s leading position will make the supply chain performance better and hence the supplier can obtain more profit than the equal power situation could explain this exception. (2) We can also educe p***<p*= p**, p*- w*< p***-w***< p**-w**, and Uπr***>Uπr**> Uπr*. That is to say, the retailer’ can charge lower retail price but get higher marginal profit hence higher utility with power grows but doesn’t exceed the supplier’s power. As he becomes the Stackelberg leader, he can gain more marginal profit hence more utility and at the same time keep the retail price unchanged. (3) Uπ***>Uπ**= Uπ*, so CE of the Nash game is higher than of the Stackelberg game. 6 Conclusion The first part of this paper studied the optimal solutions of a supplier-Stackelberg game and the integrated firm performance of the two-echelon supply chain system with stochastic price-dependent demand and symmetric information. 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