قدرت و وابستگی متقابل در روابط تامین کننده خریدار: یک روش پرتفوی خرید

Power and interdependence are generally considered to be important concepts for understanding buyer–supplier relationships. Yet, empirical research on power and interdependence in buyer–supplier relationships is still limited. Power and interdependence issues also play an important role in Kraljic's portfolio approach, which is increasingly used by purchasing practitioners for managing different supplier relations and developing appropriate purchasing strategies. In this paper, the concepts of power and interdependence have been quantified for each quadrant of the Kraljic portfolio matrix, using data from a comprehensive survey among Dutch purchasing professionals. Several hypotheses have been tested and the findings largely confirm the theoretical expectations. The observed supplier dominance in the strategic quadrant of the Kraljic matrix is a notable finding, which indicates that even satisfactory partnerships are dominated by the supplier. Therefore, the presumed power symmetry of buyer–supplier relationships in the strategic quadrant seems no longer valid.

Purchasing portfolio models have received much attention in recent literature about professional purchasing. Not only did Kraljic's seminal paper in the Harvard Business Review in 1983 have a broad influence on professional purchasing (see the evidence of Gelderman, 2003 and Kamann & Bakker, 2004), it has also inspired many academic writers to undertake further research into portfolio models (e.g. Bensaou, 1999, Croom, 2000, Dubois & Pedersen, 2002, Dyer et al., 1998, Gelderman & Van Weele, 2002, Gelderman & Van Weele, 2003, Lilliecreutz & Ydreskog, 1999, Nellore & Soderquist, 2000, Olsen & Ellram, 1997, Wagner & Johnson, 2004, Wynstra & ten Pierick, 2000 and Zolkiewski & Turnbull, 2002). Kraljic's model classifies a firm's purchased intermediate goods into four categories on the basis of two dimensions: (1) profit impact and (2) supply risk. Recent adaptations and refinements of Kraljic's model have led to alternative portfolio models using other classification dimensions (e.g. Bensaou, 1999, Olsen & Ellram, 1997 and Van Stekelenborg & Kornelius, 1994). However, the fundamental assumption of all portfolio models seems to be the occurrence of differences in power and dependence between buyers and suppliers (Dubois & Pedersen, 2002). Kraljic (1983) does not explicitly deal with issues of power and dependence. However, some of his recommendations obviously refer to the power structure (‘exploit power’). Others are aimed at reducing the dependence on suppliers (‘diversify’). Moreover, Kraljic (1983: 112) stated that the general idea of the portfolio approach is to “minimize supply vulnerability and make the most of potential buying power”. Therefore, power and dependence play a significant part in the Kraljic approach. Although power and dependence are generally considered important for the understanding of buyer–supplier relationships (e.g. Cox, 2001 and Frazier & Antia, 1995), it seems that they are still often overlooked factors in conceptual and empirical studies (e.g. Cox, 2001 and Maloni & Benton, 2000). Little is known about the exact way in which power and dependence in buyer–supplier relationships enter the Kraljic matrix (Dubois & Pedersen, 2002 and Gelderman & Van Weele, 2003). Moreover, the few portfolio models that do discuss power and dependence issues in relation to portfolio matrices generally focus on the strategic quadrant only (Wagner & Johnson, 2004). Buyer–supplier relationships in this quadrant can be characterized as strategic partnerships. However, many studies have acknowledged that not all supplier relationships can or should be strategic partnerships (e.g. Gadde & Snehota, 2000 and Wagner & Johnson, 2004). In fact, firms are found to benefit from entering into a variety of relationships with different suppliers (e.g. Bensaou, 1999 and Lilliecreutz & Ydreskog, 1999). Therefore, undertaking research into power and dependence in all four quadrants of the matrix for all relationship types is critically important. The aim of this paper is to empirically test hypotheses that can be deduced from the literature on power and dependence with respect to all quadrants of the Kraljic purchasing portfolio matrix. In order to do this we have defined the concepts of power and dependence in terms of buyer's and supplier's dependence. Subsequently, we have developed constructs for buyer's dependence as well as supplier's dependence. The empirical analysis is founded on a survey among 250 purchasing professionals. On the basis of the survey data we have assessed power and interdependence in buyer–supplier relationships for all quadrants of the Kraljic matrix. In general terms this study contributes to a better understanding of the (perceived) power and interdependence in buyer–supplier relationships. The organization of the paper is as follows. In Section 2 a brief overview of the Kraljic approach is given and, on the basis of recent literature, we will identify hypotheses with respect to power and dependence for each quadrant. In Section 3 the survey design and the constructs for the key variables are presented. The results of the survey are shown in Section 4. Section 5 will conclude and give suggestions for further research.

Purchasing practitioners maintain a variety of supplier relationships with different suppliers, and the management of these relationships is increasingly based on a portfolio framework. Power and dependence are generally considered to be important for understanding buyer–supplier relationships, yet these factors are often overlooked in empirical studies. Little is known about the role of power and dependence in buyer–supplier relationships from a purchasing portfolio perspective. In this study we filled this gap by first deducing hypotheses from the literature on ‘relative power’ and ‘total interdependence’ in each of the four Kraljic quadrants. Second, we empirically tested these hypotheses using data from a comprehensive survey among Dutch purchasing professionals. A comparison of the hypotheses with the empirical findings leads to the following results. The hypotheses that concerned the relative power position of the buyer and the supplier in each quadrant (Hypothesis 1a, Hypothesis 2a, Hypothesis 3a and Hypothesis 4a) were confirmed, except Hypothesis 1a. That is, we observed supplier dominance in the strategic quadrant, where one would expect a balanced power situation on basis of the literature. This provocative result sheds new light on the buyer's view on issues of power and dependence. It indicates that suppliers are perceived to dominate satisfactory partnerships. All hypotheses concerning the level of total interdependence in each quadrant (Hypothesis 1b, Hypothesis 2b and Hypothesis 3b) were confirmed. Table 9 summarizes the differences between the expectations on the basis of the literature on power and dependence, and the results from this study. Table 9. Comparison of relative power and total interdependence in the Kraljic matrix: theory and practice Relative power Total interdependence Expected Observed Expected Observed Strategic Balanced Supplier dominance Highest Highest Bottleneck Supplier dominance Supplier dominance Moderate Moderate Leverage Buyer dominance Buyer dominance Moderate Moderate Non-critical Balanced Balanced Lowest Lowest Table options The theoretical contribution of this paper lies primarily in the notion that future research can no longer assume that buyer–supplier relationships in the strategic quadrant of the Kraljic matrix are necessarily characterized by symmetric power positions. When we combine this result with the high total interdependence reported in this quadrant, we arrive at a more refined theoretical implication of this study. Future studies should take into account that a relationship which is characterized by a high involvement of buyers and suppliers does not necessarily imply a balanced power position between the parties, but can yet be satisfactory, at least from the point of view of the buyer. Furthermore, this study holds an implication for future research, which pertains to the sampling method in survey-based studies. Many studies ask respondents to express their opinions on their relationship with a single (type of) supplier, usually the key or the major supplier. This approach is justified in the case of channel studies (manufacturer–distributor), where relations often revolve around one major supplier. However, the method is also often used in studies relating to industrial relationships, in which the limitation to the dominant supplier is not a self-evident point of departure. Alternatively, many studies invite respondents to answer questions referring to ‘their suppliers’ in general. On the basis of this study we conclude that neither approach provides a comprehensive insight into buyer–supplier relationships. We have found evidence of the existence of four buyer–supplier relationships that differ significantly with respect to relative power and interdependence. This result confirms the notion that companies maintain a portfolio of differentiated supplier relationships. Therefore, neither reference to ‘a key supplier’ nor reference to ‘suppliers’ in general takes into account the full variation in the actual supplier base of a company. This common practice among researchers should only be used if the research question specifically requires such a sampling method. In all other cases it should be discarded. Future and further surveys can no longer ignore the large variety in supplier relationships. The findings also have managerial relevance. They offer evidence that in the strategic quadrant a supplier-dominated partnership is perceived to be satisfactory from the perspective of the buyer. Industrial marketers should be aware that professional purchasers feel dominated by them, even in satisfactory relationships. Possibly this finding could entice marketers to try to exploit their power and to skim off the market surplus. However, marketers should be aware of the negative effects of the exploitation of their position. In fact, a situation in which the buyer feels dominated yet satisfied is desirable, since the buyer will not search for alternatives (suppliers or products). Therefore, marketers should nurture these kinds of relationships. For professional purchasers the managerial implication of this study is that they should be aware that dependence implies vulnerability. Buyers should ask themselves whether there are sufficient benefits attached to the relationship to offset the obvious disadvantages of such a vulnerable and dependent position towards a supplier. In addition, purchasers should assess the risks that are harbored in this kind of relationship, and explore possibilities that might increase the bargaining power of their company. In other words, even in satisfactory relationships, buyers should explore the market by scouting for alternative suppliers and determining their competencies. Furthermore, professional purchasers should become aware of their own power basis. They should investigate to what extent the perceived supplier dominance is based on an objective assessment of the relationship. Despite the rigor of the analysis, this study contains several limitations that might entice further research. One of the limitations of the study concerns the fact that the survey was confined to the perspective of the buyer. Yet, buyer–supplier relationships are dyadic in nature. Suppliers might have different opinions on the power and interdependence structure of the various buyer–supplier relationships. Therefore, there is a need to more fully study the supplier's perspective in order to establish whether or not both parties perceive each other's power position in the relationship in the same way. Another limitation concerns the sample, which was drawn from a list of members of the Dutch Association of Purchasing Management (NEVI). Although the sample included a wide range of industry sectors, the generalizability of the results would benefit from the inclusion of firms in the service sector, as well as other Dutch and international companies. This might be the object of a further study. With respect to additional issues for further research we propose the following. The finding that buyers feel dominated by the supplier in the strategic quadrant calls for further research to identify the circumstances under which supplier dominated relationships provide a problem for the buyer (Frazier & Antia, 1995). Additionally, the operationalisation in this study could serve as a promising point of departure for further quantitative research to the issues of power and dependence in buyer–supplier relationships. The level of relative power might be related to the sizes of the buying and the supplying companies. Alternatively, network positions or the positions in the supply chain could be included as a determining factor of relative power.