European Journal of Operational Research 211 (2011) 263–273 Contents lists available at ScienceDirect European Journal of Operational Research journal homepage: www.elsevier.com/locate/ejor Production, Manufacturing and Logistics A game theoretic approach to coordinate pricing and vertical co-op advertising in manufacturer–retailer supply chains Mir Mehdi SeyedEsfahani a,⇑, Maryam Biazaran a, Mohsen Gharakhani b a b Department of Industrial Engineering, AmirKabir University of Technology, Tehran 15875-4413, Iran Department of Industrial Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran a r t i c l e i n f o Article history: Received 23 March 2010 Accepted 15 November 2010 Available online 23 November 2010 Keywords: Marketing Supply chain coordination Pricing Vertical cooperative advertising Game theory a b s t r a c t Vertical cooperative (co-op) advertising is a marketing strategy in which the retailer runs local advertising and the manufacturer pays for a portion of its entire costs. This paper considers vertical co-op advertising along with pricing decisions in a supply chain; this consists of one manufacturer and one retailer where demand is influenced by both price and advertisement. Four game-theoretic models are established in order to study the effect of supply chain power balance on the optimal decisions of supply chain members. Comparisons and insights are developed. These embrace three non-cooperative games including Nash, Stackelberg-manufacturer and Stackelberg-retailer, and one cooperative game. In the latter case, both the manufacturer and the retailer reach the highest profit level; subsequently, the feasibility of bargaining game is discussed in a bid to determine a scheme to share the extra joint profit. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Supply chain coordination has been the focus of many research studies without which channel members tend to maximize their own profit. A prime example associated with such an uncoordinated system is ‘‘double marginalization’’, in which the retailer makes arbitrary decisions without considering supplier’s profit margin (Spengler, 1950). Another example is the ‘‘bullwhip effect’’ which occurs when supply chain members make decision ignoring the others; this, in return, will lead to the spread of distorted demand information moving upstream (Lee et al., 1997). Sahin and Robinson (2002) proposed two key drivers of supply chain performance involving information sharing and coordination. Fugate et al. (2006) classified supply chain coordination mechanisms into three categories: (1) price coordination, (2) non-price coordination and (3) flow coordination. Based on this classification, pricing and vertical cooperative advertising, two business decisions discussed in this paper, are placed in the first and second category, respectively. A considerable amount of research has been conducted in recent years on different aspects of supply chain coordination including pricing, production, purchasing, inventory, etc. In this paper, optimal pricing and vertical co-op advertising decision is discussed in a single-manufacturer–single-retailer supply chain in which ⇑ Corresponding author. Tel.: +98 66466497; fax: +98 2188500995. E-mail addresses: msesfahani@aut.ac.ir (M.M. SeyedEsfahani), iicty@aut.ac.ir (M. Biazaran), gharakhani@iust.ac.ir (M. Gharakhani). 0377-2217/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ejor.2010.11.014 consumer demand is influenced by both price and advertising efforts. Manufacturers and retailers use advertising programs to convince customers to purchase their products. Their efforts are different in the sense that, the aim of manufacturer’s national advertising is to influence potential customers and raise brand awareness, while the Retailer’s local advertising is intended to bring potential customers to the point of desire and action (Huang and Li, 2001). Vertical co-op advertising is an arrangement whereby a manufacturer agrees to pay for a portion or the entire costs of local advertising undertaken by a retailer. The percentage of local advertising cost that the manufacturer agrees to pay is called ‘‘participation rate’’ (Bergen and John, 1997). The main reason for the manufacturer to use co-op advertising is to strengthen the brand image and promote immediate sales at the retail level (Hutchins, 1953). The vertical co-op advertising plays an important role in firms’ marketing programs. Total expenditures on co-op advertising in the United States in 2000 were estimated at $15 billion; an approximately fourfold increase in real terms compared with $900 million in 1970 (Nagler, 2006). Berger (1972) was the first to address the vertical co-op advertising problem mathematically. Using a real world application, he showed the proposed quantitative analysis can be applied in determining the optimal decisions appropriately. A common approach in the literature to analyze the role of coop advertising in supply chain coordination is to use game theoretical models; these exist in two categories: static and dynamic. In static models, interactions among supply chain members are discussed in a single period. Examples in this category are Dant and 264 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 Berger (1996), Bergen and John (1997), Kim and Staelin (1999), Karray and Zaccour (2006, 2007), Huang and Li (2001), Huang et al. (2002) and Li et al. (2002). In dynamic models, a goodwill function is introduced to express the carry-over effect of advertising. Most of the studies in this category ignore the participation rate despite its fundamental role. Reader is referred to Jørgensen et al. (2001, 2000) and Jørgensen and Zaccour (2003b) for more examples. On the other hand, when the retailer has perfect knowledge about manufacturer’s decision in advertising policy or in the case it has already been announced, the required assumptions of game-theoretic model do not hold. Berger et al. (2006) considered such issue in co-op advertising problem. Determining retail/wholesale price has been the focus of many studies, as a fundamental task in the supply chain management literature. Jeuland and Shugan (1983, 1988), McGuire and Staelin (1983), Moorthy (1988), Ingene and Parry (1995a,b, 1998, 2000) and Choi (1991, 1996) discuss channel coordination in the context of two-level supply chain; they do this by adopting two common pricing mechanisms as well as two-part tariffs and quantity discounts. There are a number of studies that consider pricing and advertising decisions simultaneously in supply chain coordination. Jørgensen and Zaccour (1999) proposed a differential game model in which they consider pricing and advertising decisions in a two-level supply chain under channel conflict and coordination. In their study, consumer demand is influenced by retail price and advertising goodwill. Jørgensen et al. (2001), considered the leadership role in a single-manufacturer–single-retailer marketing channel; each player controls her advertising and margin. In their model, consumer demand is influenced by both advertising goodwill and retail price. They proposed four game-theoretic models and compared the results. Jørgensen and Zaccour (2003a) also modeled consumer demand as the multiplicative product of retail price and advertising goodwill in dynamic setting, and then compared results in coordinated strategies with all those of uncoordinated. In the static framework, Yue et al. (2006) extended the model of Huang et al. (2002); they did this by considering a price-sensitive demand and studied the impact direct discount from manufacturer to the costumer may have on the channel coordination. In his paper, Zaccour (2008) attempted to study the conditions that may lead the manufacturer to achieve the integrate channel solution by means of a two-part tariff wholesale price. He further compared static and dynamic models in which demand function is affected by price and advertising. He et al. (2009) modeled a single-manufacturer– single-retailer supply chain as a stochastic Stackelberg differential game; in this game the demand is a function of both retailer’s price and advertising. Szmerekovsky and Zhang (2009) considered pricing and advertising in a two-member supply chain; where costumer demand depends on both retail price and advertisement. They obtained both the manufacturer and the retailer’s optimal decisions by solving the Stackelberg-manufacturer. Xie and Neyret (2009) and Xie and Wei (2009) followed a similar approach; they compared the cooperative game optimal results with those of non-cooperative. Xie and Neyret (2009) investigated four game models, three of which were non-cooperative and one was cooperative; whereas, Xie and Wei (2009) only considered two game models including Stackelberg-manufacturer and cooperative game. This paper is closely related to the last three studies just mentioned. According to Choi (1991), different demand-price functions lead to considerably different results. Following Choi’s results, in this paper, a relatively general demand function is proposed, compared to what Xie and Wei (2009) did in their model. In addition, we investigate one cooperative and three non-cooperative gametheoretic models; in contrast to only two models discussed by Xie and Wei. Major differences between this paper and three most related studies mentioned above are summarized in Table 1. To our best knowledge, most of the studies in the subject of power balance have assumed a dominant manufacturer. This considers the manufacturer as leader and the retailer as follower (Berger, 1972; Somers et al., 1990). Nowadays, this issue is the focus of many research studies (e.g. see Kumar, 1996; Kadiyali et al., 2000; Geylani et al., 2007). There exist some different approaches in the supply chain coordination; for instance, consider a powerful manufacturer, such as P&G, who is able to order certain shelves in her retailer’s stores, whereas a powerful retailer, such as Wal-Mart, is able to limit manufacturer’s margin or demand extra requirements including RFID attachment, inventory management, quality control, etc. Keeping in mind both approaches, we propose four scenarios including (1) equal power as in Nash game, (2) powerful manufacturer or Stackelberg-manufacturer game, (3) powerful retailer or Stackelberg-retailer game and (4) the state of integration or cooperation game. The remainder of the paper is organized as follows: in Section 2, the model framework is presented. Four game-theoretic models based on one cooperative and three non-cooperative games are discussed in Section 3. Section 4 is dedicated to illustrate the results of four proposed models. The feasibility of cooperation and solution of bargaining game is discussed in Section 5. Finally, the conclusion including summary of the main results and some directions for future research is given in Section 6. Proofs of all propositions appear in the Appendix. 2. Model framework Consider a supply chain that consists of a single manufacturer, selling her products through a single retailer that, in turn, sells the manufacturer’s product only. The manufacturer decides on the wholesale price w, National advertising expenditures A, and participation rate t. The retailer, on the other hand, decides on the retail price p and local advertising costs a. Bearing in mind the prevalent assumption in the literature (Jørgensen and Zaccour, 1999, 2003a; Yue et al., 2006; Szmerekovsky and Zhang, 2009; Xie and Wei, 2009; Xie and Neyret, 2009), it can be assumed that the consumer demand D(p, a, A) to have the following form: Dðp; a; AÞ ¼ D0 gðpÞ hða; AÞ; ð1Þ Table 1 Comparing the current paper with three most related studies. Demand function Price effect Szmerekovsky and Zhang (2009) p e (e > 1) Xie and Neyret (2009) Xie and Wei (2009) Proposed model a1 b1p (a1, b1 > 0) a1 b1p (a1, b1 > 0) ða1 b1 pÞv ða1 ; b1 > 0Þ pffiffiffi pffiffiffi k1 a þ k2 A ðk1 ; k2 > 0Þ N SM SR Co Advertising effect a2 b2acAd (a2, b2,c, d > 0) a2 b2acAd (a2, b2,c, d > 0) pffiffiffi pffiffiffi k1 a þ k2 A ðk1 ; k2 > 0Þ Game structures – SM – – N SM SR Co – SM – Co 1 p, retail price; a, local advertising expenditures; A, national advertising expenditures; N, Nash game; SM, Stackelberg-manufacturer game; SR, Stackelberg-retailer game; Co, cooperation game. 265 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 where D0 is the base demand, g(p) and h(a, A) reflect the effect of retail price and advertising costs on demand, respectively. Based on the concept of price elasticity, the demand to a product changes when its price changes; in other words, an increase in the price results in a decrease in demand. Change in quantity demanded in response to price change becomes excessive for the product that has a higher elasticity, and this product type is called highly elastic. Based on the economic interpretation of the price elasticity of demand, it p can be derived for proposed demand function as Ed ¼ ð1=v Þ 1p . There exist two kinds of demand curve involving straight line and non-linear. The reader interested in price elasticity of demand is referred to Begg et al. (2002). In the literature, practitioners proposed different demand functions of all possible curvatures including straight line, convex and concave (Hsu, 2006; Batten, 1988; Choi, 1991). As proposed by Piana (2004), three types of society bring about different shapes of demand curve. The linear demand curve arises when the reserve prices follow a uniform distribution. While, a concave demand curve arises when a wide number of consumers have the same middle reserve prices and only few rich or poor exist. By contrast, a polarized distribution of reserve price with most consumers having low reserve prices and only few are rich or middle leads to a convex demand curve. Unlike the common assumption of the linear relationship between demand and retail price, in this paper, g(p) is assumed to have a relatively general form as: 1 gðpÞ ¼ ða bpÞv ; ð2Þ where a, b and v are positive constants. Values of v < 1, v = 1, and v > 1 yields convex, linear and concave demand-price curves, respectively. The advertising effect h(a, A) is seen in a similar way as mentioned by Xie and Wei (2009): pffiffiffi pffiffiffi hða; AÞ ¼ k1 a þ k2 A; ð3Þ where k1 and k2 are positive constants that, respectively, reflect the effectiveness of local and national advertising in generating sales. As it can be observed from Eq. (3), h(a, A) is an increasing concave function of both a and A. Since the additional advertising generates continuously diminishing returns, it would be consistent with the ‘‘advertising saturation effect’’. Such effect is concluded to characterize the shape of sales-advertising function (Simon and Arndt, 1980). Kim and Staelin (1999) and Karray and Zaccour (2006) used a similar approach to link sales and advertising efforts. Combining Eqs. (1)–(3), the demand function would be the following: pffiffiffi pffiffiffi 1 Dðp; a; AÞ ¼ D0 ða bpÞv ðk1 a þ k2 AÞ: ð4Þ In order to avoid negative demand, the following condition should be verified: Dðp; a; AÞ > 0 ) p < a b ð5Þ : The profit functions of the two channel members and the system as a whole are calculated as: pffiffiffi 1 pffiffiffi Pm ðw; A; tÞ ¼ D0 ðw cÞða bpÞv ðk1 a þ k2 AÞ A ta; 1 pffiffiffi pffiffiffi Pr ðp; aÞ ¼ D0 ðp w dÞða bpÞv ðk1 a þ k2 AÞ ð1 tÞa; 1 pffiffiffi pffiffiffi Pmþr ðp; a; AÞ ¼ D0 ðp c dÞða bpÞv ðk1 a þ k2 AÞ A a; ð6Þ the whole system. To avoid the backwash effect of the profit in Eqs. (6)–(8), we have: Pm > 0 ) w > c; Pr > 0 ) p > w þ d > w; Pmþr > 0 ) p > c þ d: Combining Eq. (5) and the last inequality, it can be concluded that a b(c + d) > 0. To simplify the analysis process throughout this paper, we use an appropriate change of variables similar to the one used by Xie and Neyret (2009): a0 ¼ a bðc þ dÞ; p0 ¼ b a0 ðp ðc þ dÞÞ; 0 k1 ¼ D0 a0v1þ1 b k1 ; w0 ¼ 0 k2 ¼ D0 b a0 ðw cÞ; a0v1þ1 b k2 : Based on the above equations, we have: p< a b () bp bðc þ dÞ < a bðc þ dÞ () bðp ðc þ dÞÞ a bðc þ dÞ < 1 () p0 < 1; p > w þ d () p ðc þ dÞ > w c () p0 > w0 : By applying the above changes to Eqs. (6)–(8), it can be rewritten as follows: 1 pffiffiffi pffiffiffi P0m ðw0 ; A; tÞ ¼ w0 ð1 p0 Þv k01 a þ k02 A A ta; pffiffiffi pffiffiffi 0 0 P ¼ ðp w Þð1 k1 a þ k2 A ð1 tÞa; pffiffiffi pffiffiffi 1 P0mþr ðp0 ; a; AÞ ¼ p0 ð1 p0 Þv k01 a þ k02 A A a: 0 0 r ðp ; aÞ 0 0 1 p0 Þv ð9Þ ð10Þ ð11Þ For the sake of simplicity, we will remove the superscript (0 ) in the sequel. 3. Four game models In this section, four game-theoretic models based on three noncooperative games including Nash, Stackelberg-manufacturer and Stackelberg-retailer (SM and SR in the sequel) with one cooperative is discussed. 3.1. Nash game When the manufacturer and the retailer have the same decision power, they determine their strategies independently and simultaneously. This situation is called a Nash game and the solution to this structure is the Nash equilibrium. To determine the Nash equilibrium, manufacturer and retailer’s decision problems are solved separately and these are as follows: max 1 pffiffiffi pffiffiffi Pm ðw; A; tÞ ¼ wð1 pÞv ðk1 a þ k2 AÞ A ta ð7Þ max 0 6 A and 0 6 t 6 1; pffiffiffi pffiffiffi 1 Pr ðp; aÞ ¼ ðp wÞð1 pÞv ðk1 a þ k2 AÞ ð1 tÞa ð12Þ s:t: 0 6 w 6 1; ð13Þ s:t: w 6 p 6 1 and 0 6 a: ð8Þ where c and d are positive constants, respectively, denoting the manufacturer’s unit production cost and the retailer’s unit handling cost, in addition to purchasing cost w. Throughout this paper, subscripts m,r, and m + r represent the manufacturer, the retailer and An obvious result is that the optimal value of t would be zero in the manufacturer’s point of view, since it has a negative coefficient in the objective function (12). In addition, Pm is increasing in line with w, which means the optimal value for w is p. However, since p > w, w cannot be equal to one, or otherwise there would be no 266 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 profit for both sides. We apply a similar approach as proposed by Jørgensen and Zaccour (1999) and Xie and Neyret (2009) to tackle the problem; we assume that the retailer will not sell the product if she does not get a minimum unit margin. We take manufacturer’s unit margin as such minimum level and replace the wholesale price constraint with: lr > lm ) p w P w ) w 6 p=2; where lr = p w and lm = w are retailer’s and manufacturer’s unit margins, respectively. Hence, the optimal value of w is 2p. t ¼ 0; p w¼ ; 2 2 1 k2 wð1 pÞ1=v : A¼ 2 ð16Þ ð17Þ ð18Þ In order to determine the SR equilibrium, the retailer’s decision problem is solved through incorporating optimal values of t, w, A in her profit function. Proposition 3. The SR game has the following unique equilibrium: Proposition 1. The Nash game has the following unique equilibrium: wSR ¼ t N ¼ 0; v 2v pN ¼ ; 2v þ 1 2v þ 1 v2þ2 v2þ2 1 2 1 1 2 1 AN ¼ k2 v 2 a N ¼ k1 v 2 : 4 2v þ 1 4 2v þ 1 wN ¼ pSR ¼ In this section, the relationship between the manufacturer and the retailer is modeled as a sequential non-cooperative game, where the manufacturer is the leader and the retailer the follower. The solution to this structure is called the Stackelberg equilibrium. In order to obtain it, the best response of the follower and in the second stage should be determined at first. The leader’s decision problem is solved based on the follower’s response. Regarding the retailer’s solution in Nash game, the retailer’s response is as follows: 1þ1 !2 1 1w v k1 v ; 2ð1 tÞ v þ1 ð14Þ v þw p¼ : v þ1 ð15Þ Solving the manufacturer’s decision problem (12) by incorporating optimal values of a and p, the SM equilibrium can be calculated. Proposition 2. The SM game has the following unique equilibrium: 2 wSM ¼ k¼ 2v ðv þ 1Þk þ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 4v 2 ðv þ 1Þ2 k ðk þ 1Þv 2 þ ðv þ 2Þ2 2 ðv þ 2Þ2 þ 4k ðv þ 1Þ2 aSM ¼ ¼ t SM ¼ 1 wSM v þ1 ! 1=v 2 wSM k2 1 wSM ; 2 v þ1 v ð1 wSM Þ k1 v wSM ðv þ 2Þ þ v wSM ð3v þ 2Þ v ; wSM ðv þ 2Þ þ v pSM ¼ v ; v þ1 v v þ1 aSR ¼ ; k2 2 v 16 2 ASR ¼ ; k1 2 v 16 v v2þ2 1 ; v þ1 2 v þ2 1 : þ1 t SR ¼ 0; The previous three subsections discussed three non-cooperative games. Now, we model the manufacturer–retailer relationship as a cooperative game in which both channel members agree to cooperate and maximize the profits of the whole system. Proposition 4. The cooperation game has the following unique solution: A ¼ 1 k2 v 2 pco ¼ v : v þ1 co 1 v þ1 v1þ1 !2 ; co a ¼ 1 k1 v 2 v v1þ1 !2 1 ; þ1 The solution (pco, aco, Aco) gives the maximum profits for the whole system. The wholesale price w and participation rate t, are open to take any value between zero and 1. Despite this, it is obvious that the individual profit of neither the manufacturer nor the retailer is not independent of w and t. Both sides would participate in the cooperation only if their individual profits are higher than those of non-cooperative cases. Thus, we will discuss the feasibility of the cooperative game in the next section. Table 2 summarizes the optimal solution of four game models. ; 4. Discussion of the results k2 ; k1 1þ1 !2 2 v 3.4. Cooperation 3.2. Stackelberg-manufacturer game a¼ 1 2 ASM v þ wSM : v þ1 3.3. Stackelberg-retailer game We now model the manufacturer–retailer relationship as a sequential non-cooperative game in which the retailer has more decision power, and is the leader. The solution to this structure is called the SR equilibrium. The first step in determining it, similar to the previous section, is to find the best response of the manufacturer. The manufacturer response as provided in Section 3.1 is: In this section, we will discuss the comparisons among the optimal solution of the four games. All the presented comparisons are given based on different values for the parameters k and v. The parameter k, reflects the effectiveness of national advertising versus local advertising and is defined as k = k2/k1. The parameter v, defines the shape of demand-price function. The demand-price function would be linear, convex or concave on condition that v is equal to, less than or greater than 1, respectively. Comparisons are independent of values for k1 and k2. Considering the optimal solution summarized in Table 2, all of the decision variables are some function of the values k and v; this means the optimum decisions of both sides can be calculated through estimating these two parameters. This would make the issue of determining these parameters more challenging, since the quality of the results depends greatly on the quality of the estimated parameters. Therefore, to determine the best policy, both decision makers should estimate these parameters at first. To do so, one should start a deep market research in order to specify the behavior of the demand to advertisement, both national and local. The parameters k1 and k2 are positive constants which measure 267 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 Table 2 Summary of the optimal solutions in four game models. Nash game SM game pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 2 2 2 Wholesale price w v 2v þ1 2v ðv þ1Þk þ Retail price p 2v 2v þ1 v þwSM v þ1 National advertising A Local advertising a 1 2 4 k2 v2 1 2 4 k1 v2 v2þ2 1 2v þ1 2 v þ2 1 2v þ1 wSM k2 2 4v v þ1Þ k ðk þ1Þþv 2 ðv þ2Þ2 þ4k ðv þ1Þ2 Participation rate t 0 wSM ð3v þ2Þv wSM ðv þ2Þþv Price elasticity of demand Ed 2 1 k¼ v v þwSM 1wSM k1 v SR game Cooperation game 1 v 2 v þ1 – v v þ1 k22 16 1w v þ1 v ð1wSM Þ wSM ðv þ2Þþv v þ2Þ 2ð 2 SM 1=v 2ð 1 þ1 1wSM v v þ1 2 2 k1 16 v2 v2 1 v2þ2 v v þ1 1 2 k2 v þ1 1 v2þ2 1 2 k1 v þ1 0 – 1 1 v v 1 v1þ1 2 1 v1þ1 2 v þ1 v þ1 k2 . k1 the potential increase in sales due to an increase in advertising costs for both retailer and manufacturer, respectively. Since all optimal solutions are some functions of v, it should be estimated precisely. Necessity of a good and its corresponding parameter v are inversely related; the higher the degree of necessity, the lower the value of v (e.g. for luxury goods v seems to increase). Different amounts for the shape parameter may be found in different industries depending on the nature of goods provided and the behavior of their final consumers. In this paper, our distinct contribution is to provide a flexible environment which enables the decision maker to recognize the shape of demand function and obtain the right parameters of the identified model using market data. As mentioned before, a special form of this problem has been discussed earlier in the literature where shape parameter assumed to be 1 (Xie and Wei, 2009). This paper supposes a more general and flexible model. Fig. 1. Retail and wholesale prices. 4.1. Comparisons on prices The summary of the results provided in Table 2 show that the optimal retail prices in the SR and the cooperation game are the same. It is obvious that the optimal retail price in the Nash game is higher than those in SR and cooperation. In the SM game, the retail price is higher than when the retailer is the leader, because the manufacturer imposes a higher wholesale price, hence, in order to obtain a tolerable profit margin, the retailer chooses a higher price. Fig. 1 illustrates the comparison between optimal values of wholesale price and retail price in four game models. It can be observed from Fig. 1 that the resulting optimum solution divides the parameters space into two distinct regions. In region (I) the optimal price for the Nash game is higher than that of MS, whereas in region (II) both retail and wholesale prices for SM game are higher than that of Nash. 4.2. Comparisons on advertising expenditures Fig. 2. National advertising expenditures. Taking the summarized solutions in Table 2 into consideration, the following simple outcome about the retailer’s advertising is obtained: 8ðk; v Þ : aco > aSM > aSR > aN : The highest local advertising expenditure is made in the cooperative game and the lowest occurs in the Nash game. When the manufacturer is the leader, the retailer spends more on advertising, because the manufacturer participates in local advertising cost, tSM > 0. As illustrated in Fig. 2, the highest national advertising expenditure occurs in the cooperation, the same result as in local advertising case. Depending on the values of the parameters k and v, the comparison results are different. However, one may believe that the manufacturer spends more on national advertising when she is the follower to the retailer rather than in the Nash Game in all three regions. 4.3. Comparisons on participation rate As shown in Table 2, the manufacturer’s participation rate in retailer’s local advertising expenditures equals zero in both Nash game and SR game. Fig. 3 illustrates the behavior of the optimal participation rate w.r.t. k and v in the SM game. When the effectiveness of local advertising is higher than that of national efforts, the lower participation rate is preferred by the manufacturer. On 268 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 Fig. 3. Participation ratio tSM. the other hand, lower values of m will result in lower participation rate. 4.4. Comparisons on profits Fig. 5. Retailer’s profits. The profit is the most important performance measure in supply chain. Fig. 4 compares the optimal profit of the manufacturer, obtained in three non-cooperative models. It can be implied that the manufacturer prefers to play the Stackelberg with retailer rather than to be in conflict situation with the retailer in the Nash game. Moreover, in region (I), the manufacturer desirably prefers to be the retailer’s follower than to be the channel’s leader; while, in region (II), the manufacturer prefers to be the leader. As illustrated in Fig. 5, the retailer prefers to play the Stackelberg game in all three regions rather than to play separately as in the Nash game. The retailer naturally prefers to be the leader of the channel, whereas she agrees to be the follower in region (I). Fig. 6 compares the whole system’s profits across four games. As a popular result in the literature, the highest profit will be achieved in the cooperation case; i.e. the channel members decide to make decision cooperatively in order to maximize the whole system’s profits. In regions (I) and (II) total profit of the supply chain has a higher level in Stackelberg game considering retailer as the leader. Even though playing SM game will result in higher total profit as shown in region (III). Furthermore, in regions (II) and (III) the Stackelberg Fig. 6. System’s profits. game has a higher profit than Nash game. Whereas, surprisingly total profit has a higher level in the Nash game compared with SM game. 4.5. Feasibility of the cooperation game Fig. 4. Manufacturer’s profits. In Section 3.4, we reached the analytical solution to the cooperative game, and observed that the manufacturer and the retailer will only agree to make joint decisions if their individual profit is higher in the cooperative game than in the non-cooperative ones. In this section, we use the comparison results in Section 4.4 to ver- M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 269 ify the feasibility of this problem. In order to understand this, we need to show that (pco, wco, aco, Aco, tco) exists: co co SM SR N max co co co Pco m ¼ Pm ðp ; w ; a ; A ; t Þ P max Pm ; Pm ; Pm ¼ Pm ; ð19Þ co co SM SR N co co co Pco : ¼ Pmax r ¼ Pr ðp ; w ; a ; A ; t Þ P max Pr ; Pr ; Pr r ð20Þ By integrating Eqs. (19) and (20), equivalently we have: co co max max Pco : mþr ¼ Pm þ Pr P Pm þ Pr ð21Þ By combining Figs. 4 and 5, Fig. 7 is obtained, which has five regions. Table 3 determines the maximum profits of the manufacturer and the retailer in each region. The next step is to verify the condition in Eq. (21) for each region of Fig. 7 to understand if a feasible solution is achieved. In region (I), the maximum profit of the manufacturer corresponds to the SR game, while the retailer’s is obtained in the SM game. Fig. 8 illustrates the relative difference between cooperation and non-cooperation. D1 ¼ SR SM Pco mþr Pm þ Pr Pco mþr Fig. 8. Relative difference D1in regions (I). 100: According to Fig. 8, the relative difference is positive, hence, the condition in Eq. (21) holds true and the feasible solution is certain to exist. The comparison results in regions (II) and (III) are identical and imply that the maximum profit of both sides is obtained in the SR game. As illustrated in Fig. 6, it is obvious that the condition in Eq. (21) holds true in these two regions, as the cooperation case yields the highest profits for the whole system. Thus, the cooperation game is feasible in these two regions. In regions (IV) and (V), the maximum profits of the retailer and the manufacturer are ob- Fig. 9. Relative difference D2in regions (IV) and (V). tained, respectively in the SR and the SM. Similar to the approach used in region (I), Fig. 9 illustrates the relative difference D2 between cooperation and non-cooperation; this displays that the condition in Eq. (21) holds true in these two regions and the feasibility of the cooperation is obvious. D2 ¼ Fig. 7. Five regions to discuss the feasibility of the cooperation game. Table 3 Maximum profit of supply chain members in five regions of Fig. 7. Pmax m Pmax r (I) PSR m PSR m PSM m PSM r PSR r PSR r (IV) and (V) Pco mþr 100: We showed that the cooperation game is feasible; therefore, this resulted in the manufacturer and the retailer’s willingness to cooperate. The next issue that is to be resolved is the sharing of the extra gained profit. The profit-sharing problem is discussed in Section 5. 5. Bargaining problem Region (II) and (III) SR SM Pco mþr Pm þ Pr In this section, a feasible region for the variables w and t is presented. Finally, the Nash bargaining model will be used to solve the profit-sharing problem in this region. We use a similar approach employed by Xie and Wei (2009) and Xie and Neyret (2009) to 270 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 illustrate the feasible region for this problem. The extra profit of the manufacturer and the retailer are as follows: co m km km DP ¼ ðD CÞ; km þ kr km þ kr kr kr DPr ðw ; t Þ ¼ DP ¼ ðD CÞ; km þ kr km þ kr Ckm þ Dkr ) w B t aco ¼ : km þ kr DPm ðw ; t Þ ¼ max m DPm ¼ P P pffiffiffiffiffiffi pffiffiffiffiffiffiffi ¼ wð1 pco Þ1=v k1 aco þ k2 Aco Aco taco Pmax m ¼ wB taco C > 0; max DPr ¼ Pco r Pr ¼ ðp wÞð1 The solution to this problem is as follows: 1 pco Þv ð22Þ pffiffiffiffiffiffi pffiffiffiffiffiffiffi k1 aco þ k2 Aco ð1 tÞaco Pmax r ¼ wB þ taco þ D > 0; ð23Þ where B, C and D are chosen as follows: pffiffiffiffiffiffi pffiffiffiffiffiffiffi B ¼ ð1 pco Þ1=v k1 aco þ k2 Aco > 0; > 0; C ¼ Aco þ Pmax m D ¼ pco B aco Pmax > 0: r Inequalities (22) and (23) specify region between two parallel lines as illustrated in Fig. 10. Every pair (w, t) in this region presents a feasible solution to the bargaining problem. The closer this point approaches the line, Pm ¼ Pmax the lower the manufacturer’s m share and the higher the retailer’s. All the pairs (w, t) located on a line parallel to Pm ¼ Pmax lead to the same profit for m max Pm ¼ Pmax þ DPr for the m þ DPm the manufacturer and Pr ¼ Pr retailer. According to Nash (1950), the bargaining outcome (w⁄, t⁄) is obtained by maximizing the product of individual utilities over the feasible solution. Consider the following utility functions for the manufacturer and the retailer: um ðw; tÞ ¼ DPm ðw; tÞkm ; ur ðw; tÞ ¼ DPr ðw; tÞkr : To obtain the Nash’s solution, the following optimization needs to be solved: Max um ðw; tÞ:ur ðw; tÞ ¼ DPm ðw; tÞkm :DPr ðw; tÞkr : ð24Þ Eq. (24) presents a line parallel to Pm ¼ Pmax m . If km > kr, this line would be closer to Pr ¼ Pmax , hence, the manufacturer’s share of r the extra profit will be greater than the retailer’s, and vice versa. When km = kr, then the manufacturer and the retailer will split the extra profit equally. In this section, we learn about the relationship (24) between the optimal values of t and w in the cooperation game. Without any further assumptions, determination of individual values of w and t is impossible. 6. Conclusions Optimal decisions of pricing and vertical co-op advertising in four game-theoretic models are derived; these consist of one cooperative three non-cooperative games in a single-manufacturer– single-retailer supply chain. At this point, the consumer demand is influenced by both price and advertising expenditures. In the proposed model, the relationship between price and demand has a relatively general form compared with the classic linear relationship. Comparison results reflect the significant effect the shape of demand-price function (i.e. linear, convex or concave) may have on optimal values of decision variables and supply chain members’ profit. The practical aspects of our proposed model include addressing the advertising saturation effect in demand function modeling and different channel structures (cooperation, Nash game and the case of dominant member). The results show that the retail price is the lowest when two members of the supply chain decide to cooperate, whereas the advertising expenditures are higher in non-cooperative games. Also the highest amount of profit for the whole system is achieved in cooperation case. It has also been shown that the manufacturer prefers to be the retailer’s follower rather than to be in conflict situation (Nash game). The feasibility of the cooperation game is verified, and the feasible region for the bargaining problem is defined. This is the point when supply chain members can share the extra-profit gained by the cooperation. The Nash bargaining model is used to solve the bargaining problem. The optimal values for participation rate and wholesale price for the cooperation game are not specified individually, however, a relationship between their optimal values is derived. There are several possible directions for the future studies. First, one can involve more decision-makers to enrich the results and add competitive characteristics to the model. Second, one can adopt a different form of demand function and finally, other bargaining schemes may be applied in order to achieve different results. Acknowledgment The authors are grateful to the referees for their valuable comments and illustrative suggestions. Appendix Fig. 10. Feasible region of the bargaining problem. Proof of Proposition 1. The second partial derivative of Pm in Eq. (12) w.r.t. A is negative, hence, Pm is concave w.r.t. A and the optimal value is achieved by solving the first order condition: 271 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 1 1 @ Pm 1 ¼ k2 wð1 pÞv A2 1 ¼ 0 ) A ¼ 2 @A 2 1 1 k2 wð1 pÞv : 2 ðA1Þ To solve the retailer’s problem (13), we define variable x as 1 ðp wÞð1 pÞv . To determine the domain of x, we solve the first order equation below and compare the critical value with values of x at p = 0 and p = w: 1 @x 1 v þw ¼ ð1 pÞv 1 ðv pðv þ 1Þ þ wÞ ¼ 0 ) p1 ¼ 2 ðw; 1Þ; @p v v þ1 p ¼ w ) x ¼ 0; p ¼ p1 ¼ v1þ1 v þw 1w )x¼v v þ1 v þ1 2 2 @ Pm k1 1w v ðv 2wðv þ 1ÞÞ ¼ @w 2ðv þ 1Þð1 tÞ v þ 1 pffiffiffi 11 k2 A 1w v ðv wðv þ 1ÞÞ þ v ðv þ 1Þ v þ 1 2þ1 2 tk1 v 1w v ; þ 2 2ð1 tÞ v þ 1 1 @ Pm wk2 1 w v 1; ¼ pffiffiffi @A 2 A v þ1 2þ1 2 @ Pm k1 v 1w v ð2wðv þ 1Þ v ð1 wÞ ¼ @t 4ð1 tÞ3 ð1 þ v Þ v þ 1 > 0; tð2wðv þ 1Þ þ v ð1 wÞÞÞ: p ¼ 1 ) x ¼ 0: Thus, the maximum of x is obtained while p = p1 and the minimum value of x equals zero. Now we rewrite the retailer’s decision problem as follows: max pffiffiffi pffiffiffi Pr ðx; aÞ ¼ xðk1 a þ k2 AÞ ð1 tÞa s:t: 0 6 x 6 v 1þ1 1w v and 0 6 a: v þ1 It is obvious that the retailer’s profit is increasing with x, thus, the optimal value of x is: x ¼ xmax ¼ v 1þ1 1w v : v þ1 ðA2Þ It is also obvious that Pr is concave w.r.t. a; this is because the second partial derivative of Pr w.r.t. a is negative and therefore, the optimal value of is obtained as follows: @ Pr 1 1 ¼ k1 xa2 ð1 tÞ ¼ 0 ) a ¼ @a v 1 k1 x 2ð1 tÞ 2 : ðA3Þ Solving Eqs. (A1)–(A3) considering w ¼ 2p and t = 0, we achieve the Nash equilibrium: wN ¼ AN ¼ v 2v þ 1 ; pN ¼ 1 2 2 1 k v 4 2 2v þ 1 2v ; 2v þ 1 v2þ2 ; 0 6 t 6 1 t < 1; 0 6 w 6 1 w < 1; 0 < A 6 A 6 Amax ; where t, w, A are positive constants and sufficiently close to zero. Amax is a positive constant, which is assumed to be as great as we desire, employed to restrict the solution area. The new solution area is a closed and bounded set, and the objective function is defined over it. The ‘‘extreme value theorem’’ a.k.a. ‘‘Weierstrass theorem’’, states that if a real valued function is continuous over a closed and bounded set, this function must attain its minimum and maximum value, each at least once. Over the new set of constraints, Pm verifies the conditions of the ‘‘extreme value theorem’’. Thus, we can ensure that there exists a solution to this problem. This solution must fulfill the KKT first order necessary conditions. The KKT conditions for this problem are as follows: 0 @ ð P Þ 1 0 @g 1 m i @w 6 C X C B @ ð@w B @g B Pm Þ C þ B i C ¼ 0; u i @ @t A @ @t A @ ðPm Þ @a t N ¼ 0; aN ¼ As the partial derivatives of Pm show, this function is not differentiable at t = 1, w = 1 (if v > 1) and A = 0. When participation rate t approaches 1, the profit function, in turn, approaches negative infinity. When w is equal to 1, the profit function equals A < 0. We can assume a minimum level for the national advertising expenditures, to ensure that the profit function is differentiable at this point. The new set of constraints is as follows: i¼1 g 1 ¼ w 6 0; 1 2 2 1 k v 4 1 2v þ 1 This completes the proof of Proposition 1. v2þ2 g 3 ¼ t 6 0; : h Proof of Proposition 2. Substituting Eqs. (14) and (15) into the expression of Pm , the decision problem (12) becomes: ! 1 1þ1 2 pffiffiffi 1w v k1 v 1w v Max Pm ¼ w þ k2 A A v þ 1 2ð1 tÞ v þ 1 2þ2 2 tk1 v 2 1w v 4ð1 tÞ2 v þ 1 @g i @a g 2 ¼ w ð1 w Þ 6 0; g 4 ¼ t ð1 t Þ 6 0; g 5 ¼ A þ A 6 0; g 6 ¼ A Amax 6 0; ui g i ¼ 0 for i ¼ 1; . . . ; 6; ui P 0 for i ¼ 1; . . . ; 6: Table A1 Possible combinations of active constraints. No constraint is active Only one constraint is active Only two constraints are active s:t: 0 6 w 6 1; 0 6 A; 0 6 t 6 1: Before solving this non-linear programming problem, we revise the constraints to make sure that the objective function is continuous and differentiable in the solution area. Below comes the partial derivatives of objective function (12) w.r.t. its corresponding variables. Three constraints are active Possible combinations of active constraints combinations (all ui = 0 ) g1,g2,g3,g4,g5,g6 (g1,g3), (g1,g4), (g1,g5), (g1,g6), (g2,g3), (g2,g4), (g2,g5), (g2,g6), (g3,g5), (g3,g6), (g4,g5), (g4,g6), (g1,g3,g5), (g1,g3,g6), (g1,g4,g5), (g1,g4,g6), (g2,g3,g5), (g2,g3,g6), (g2,g4,g5), (g2,g4,g6), Total 1 6 12 8 27 272 M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 All the possible combinations of active constraints are shown in Table A1. The KKT necessary conditions need to be verified for each combination in order to achieve all candidate local maximum points. Note that the constraints g1 and g2 are inconsistent; as a result, no combination with both g1 and g2 active is possible. The same result holds true for (g3, g4) and (g5, g6). By verifying KKT first order necessary conditions in 27 combinations, only one feasible KKT point can be achieved and that is where no constraint is active. 0 @ðP Þ 1 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 8 2 v 2 ðv þ1Þ2 k2 ðk2 þ1Þþv 2 ðv þ2Þ2 > ; w ¼ 2v ðv þ1Þk þ ðv4þ2Þ > 2 > þ4k2 ðv þ1Þ2 > > < 2 1w v þ1 A¼ > > > > > : v þ2Þv : t ¼ wð3 wðv þ2Þþv 1=v k ¼ kk21 ; ðA4Þ ¼ aSM ¼ ðA5Þ ; ¼ t SM ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 2 2v ðv þ 1Þk þ 4v 2 ðv þ 1Þ2 k ðk þ 1Þ þ v 2 ðv þ 2Þ2 2 ðv þ 2Þ2 þ 4k ðv þ 1Þ2 wSM ð3v þ 2Þ v ; wSM ðv þ 2Þ þ v pSM ¼ v þ wSM : v þ1 1 0 6 a: ; v þ1 2 We can conclude that Pr is an increasing function of y, therefore the optimal value for y is: y ¼ ymax ¼ v 1 2 v þ1 v1þ1 ðA7Þ : k ASM ðA8Þ By solving Eqs. (16)–(18), (A7) and (A8), The SR equilibrium would be: v ; v þ1 pSR ¼ v2þ2 wSR ¼ 1 2 ASR ¼ k2 2 v 16 2 ; k2 ; k1 1þ1 !2 1 wSM v ; v þ1 1=v !2 wSM k2 1 wSM ; 2 v þ1 v s:t: 0 6 y 6 2 @ Pr 1 1 1 k1 y : ¼ k1 ya2 1 ¼ 0 ) a ¼ 2 2 @a ðA6Þ v ð1 wSM Þ k1 v SM w ðv þ 2Þ þ v 1 2 v1þ1 Therefore, the optimal value of is achieved by solving the following first order equation: Based on the result of ‘‘extreme value theorem’’, this KKT solution is the only local maximum candidate; hence, we conclude that this point is the global maximum of Pm . Therefore we obtain the SR equilibrium solving Eqs. (14) and (15) and Eqs.(A4)–(A6) as shown below: wSM ¼ pffiffiffi @ 2 Pr 1 3 ¼ k1 ya2 < 0: 4 @a2 @ðPm Þ @a wk2 2 Pr ¼ y k1 a þ k22 y a It is also obvious that Pr is concave w.r.t. a; because the second partial derivative of Pr w.r.t. a is negative as shown below: m C B @ð@w Pm Þ C All ui ¼ 0 ) B @ @t A ¼ 0 and All g i < 0 ) max 1 v þ1 v ; v þ1 t SR ¼ 0; 2 ; aSR ¼ k1 2 v 16 1 v þ1 v2þ2 : Proof of Proposition 4. To solve this problem, we define z as p(1 p)1/v To determine the domain of z, we solve the first order equation below and compare the value of at that point with values of z while p = 0 and p = 1. 1 @z 1 v ¼ ð1 pÞv 1 ðv pðv þ 1ÞÞ ¼ 0 ) p3 ¼ ; @p v v þ1 p ¼ w ) z ¼ 0; v1þ1 v 1 p ¼ p3 ¼ > 0; )z¼v v þ1 v þ1 p ¼ 1 ) z ¼ 0: Proof of Proposition 3. Substituting Eqs. (16)–(18) into the expression of Pr , the decision problem (13) becomes: max pffiffiffi 1 p Pr ðp; aÞ ¼ ð1 pÞ1=v k1 a þ k22 pð1 pÞ1=v a 2 4 s:t: 0 6 p 6 1 and 0 6 a: To solve this problem, we define variable y as 2p ð1 pÞ1=v . To determine the domain of y, we solve the first order equation below and compare the critical value of y at that specific point with values of y at p = 0 and p = 1. 1 @y 1 v ¼ ð1 pÞv 1 ðv pðv þ 1ÞÞ ¼ 0 ) p2 ¼ ; @p 2v v þ1 p ¼ w ) y ¼ 0; 1 v 1 v þ1 > 0; p ¼ p2 ) y ¼ 2 v þ1 Hence, the maximum of z is obtained while p = p3 and the minimum value of z equals zero. Now we rewrite the decision problem as follows: max pffiffiffi pffiffiffi Pmþr ¼ z k1 a þ k2 A a A s:t: 0 6 z 6 v 1 v þ1 v1þ1 ; 0 6 a and 0 6 A: Now we derive the partial derivative of Pmþr w.r.t. z, that is: pffiffiffi pffiffiffi @ Pmþr ¼ k1 a þ k2 A > 0: @z Thus, Pmþr is an increasing function of z, therefore, the optimal value of z is: 1 v þ1 v1þ1 p ¼ 1 ) y ¼ 0: z ¼ zmax ¼ v Hence, the maximum of y is achieved at p = p2 and the minimum value of y equals zero. Now we rewrite the retailer’s decision problem as follows: The optimal values of a and A can be derived from the first order conditions below: : ðA9Þ M.M. SeyedEsfahani et al. / European Journal of Operational Research 211 (2011) 263–273 2 1 k1 z ; 2 2 1 1 1 k2 z : ¼ k2 zA2 1 ¼ 0 ) A ¼ 2 2 @ Pmþr 1 1 ¼ k1 za2 1 ¼ 0 ) a ¼ 2 @a ðA10Þ @ Pmþr @A ðA11Þ The Hessian matrix is a negative definite matrix and fulfills the second-order condition for a maximum. 2 H¼ @ 2 Pmþr 4 @a2 @ 2 Pmþr @A@a @ 2 Pmþr @a@A @ 2 Pmþr @A2 3 5¼ 2 kp 1z ffiffi 4 4a a 0 0 kp 2z ffiffi 4A A 3 5: Thus, the Eqs. (A9)–(A11) lead to the following solution for the cooperative game: A ¼ 1 k2 v 2 pco ¼ v : v þ1 co 1 v þ1 v1þ1 !2 ; co a ¼ 1 k1 v 2 1 v þ1 v1þ1 !2 ; References Batten, D., 1988. On the variable shape of the free spatial demand function. Journal of Regional Science 28 (2), 219–230. Begg, D., Fischer, S., Dornbusch, R., 2002. Economics, seventh ed. McGraw-Hill, London. Bergen, M., John, G., 1997. Understanding cooperative advertising participation rates in conventional channels. Journal of Marketing Research 34 (3), 357–369. Berger, P., 1972. 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