Int. J. Production Economics 129 (2011) 277–283 Contents lists available at ScienceDirect Int. J. Production Economics journal homepage: www.elsevier.com/locate/ijpe Supplier development and the relationship life-cycle Stephan M. Wagner n Chair of Logistics Management, Department of Management, Technology, and Economics, Swiss Federal Institute of Technology Zurich, Scheuchzerstrasse 7, 8092 Zurich, Switzerland a r t i c l e in f o abstract Article history: Received 7 July 2008 Accepted 22 October 2010 Available online 27 October 2010 The mainstream view holds that over time buyer–supplier relationships evolve through a number of phases. As a consequence, supplier development as a buyer–supplier relationship management practice should also be adapted to the life-cycle phase. Supplier development activities matching the buyer– supplier relationship life-cycle phase will lead to more favorable performance improvements. However, prior studies have neglected the relationship life-cycle perspective. This empirical study shows how the length of the buyer–supplier relationship can be used to improve the explanatory power of models investigating the performance outcomes of supplier development activities. The results show that supplier development is more effective in mature as opposed to initial and declining life-cycles phases. & 2010 Elsevier B.V. All rights reserved. Keywords: Supplier development Buyer–supplier relationship Relationship life-cycle Social capital theory Regression analysis Curvilinear relationship 1. Introduction There is ample anecdotal evidence in corporate practice and academic research that supplier development as any set of activities a buying firm expends on a supplier to improve supplier performance and/or supplier capabilities (Krause et al., 2000) can help to meet supply needs and generate favorable results for the buying firm. Recognizing the long-term and strategic benefits of supplier development, many companies have established supplier development programs and teams. Honda of America, for example, has adopted the BP (‘‘Best Practice, Best Process, and Best Performance’’) supplier development program to help suppliers in implementing the Kaizen philosophy for continuous improvement and organizational change (MacDuffie and Helper, 1997; Sako, 2004). John Deere built up a systematic supplier development approach to upgrade suppliers’ just-in-time capabilities. Working with John Deere’s supplier development teams, suppliers were able to achieve dramatic reductions in cycle time (Golden, 1999). Several aerospace and defense companies, including Boeing, Lockheed, Northrop Grumman, Rockwell Collins, Parker Aerospace, and United Technologies, joined forces and established a program called the ‘‘Supplier Excellence Alliance’’ with the goal to share best practices with suppliers and to realize improvements in quality, on-time delivery, and inventory levels at the suppliers. After a few years into the program the tier-one suppliers now began to share with their own suppliers what they have learned from the aerospace and defense companies (Avery, 2008). By consulting with the problem solving teams of Toyota’s Operations n Tel.: + 41 44 632 3259; fax: + 41 44 632 1526. E-mail address: stwagner@ethz.ch 0925-5273/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpe.2010.10.020 Management Consulting Division (OMCD) in Japan and the Toyota Supplier Support Center (TSSC) in the United States, many suppliers have received assistance in building up lean manufacturing capabilities. These organizational capabilities benefited both the suppliers and Toyota in the long run (Dyer and Hatch, 2006; Dyer and Nobeoka, 2000). Wal-Mart set up a supplier development group and a series of strategies that help the retailer to better serve customers. This group fosters close collaboration between WalMart and its suppliers and joint business planning. Consequences of these efforts include significant improvement in customer awareness of brands, successful key item launches, and increased sales (Hahn, 2005). In line with the bigger prominence of supplier development in corporate practice, scholars have lately paid increased attention to supplier development activities and programs. In 2007 alone, nine articles focusing on supplier development were published in production- and operations management-related journals (Araz and Ozkarahan, 2007; Carr and Kaynak, 2007; Chan and Kumar, 2007; Krause et al., 2007; Lee and Humphreys, 2007; Li et al., 2007; Modi and Mabert, 2007; Rogers et al., 2007; Wouters et al., 2007). All these studies and previous research on supplier development have investigated the buying firms’ supplier development activities at a single point in time and ignored the life-cycle of the buyer– supplier relationship. Scholars pointed out that suppliers with strategic partnershiplike relationships with the buying firm should be considered as potential candidates for supplier development (Araz and Ozkarahan, 2007; Talluri and Narasimhan, 2004). Likewise, Li et al. (2007, p. 231) remarked that ‘‘[i]mprovements in performance will happen within the unique exchange relationships developed between the buyer and supplier firms.’’ Since such ‘strategic partnership-like relationships’ or ‘unique exchange 278 S.M. Wagner / Int. J. Production Economics 129 (2011) 277–283 relationships’ which influence the effectiveness of buying firms’ supplier development activities develop over time, I contend that it is necessary to go beyond the study of supplier development activities at a single point in time and to take the stage of the buyer– supplier relationship into account. My study draws on social capital theory (e.g., Adler and Kwon, 2002; Inkpen and Tsang, 2005; Nahapiet and Ghoshal, 1998) to explore the performance improvements of buying firms willing to develop social capital with key suppliers through supplier development. The primary goal of the study is to explore the impact of the dynamic nature of buyer–supplier relationships on the outcome of buying firms’ supplier development activities. I test my proposed model in a cross-sectional sample by means of a quasilongitudinal analysis. More specifically, I show that different stages of the buyer–supplier relationship life-cycle moderate the relationship between supplier development and the buying firm’s performance. As such, my research refines and extends previous empirical studies on supplier development and asserts that the life-cycle of the buyer–supplier relationship should be included as a moderator in models studying the impact of supplier development and other models investigating buyer–supplier relationship practices. I next provide a review of the current literature on buyer– supplier relationship dynamics embedded within the theoretical constructs of social capital theory and previous research in management and relationship marketing. This includes the delineation of my hypothesis. Next, I describe the data and the measures, and present the analysis and results. Finally, I discuss implications for further research. 2. Theory and development of hypothesis 2.1. Time contingent value of social capital Social capital theory is an emerging concept that acknowledges the inherent value of social structures such as relationships, networks, and groups. Social capital refers to ‘‘the sum of the actual and potential resources embedded within, available through, and derived from the network of relationships possessed by an individual or social unit’’ (Nahapiet and Ghoshal, 1998, p. 243). Central to the studies using social capital theory is the idea that networks of relationships and interactions between individuals can facilitate the creation of value within firms (Inkpen and Tsang, 2005; Tsai and Ghoshal, 1998). Social capital can be defined and applied on different levels of analysis, such as individuals, groups, and organizations (Adler and Kwon, 2002). Whereas some relationships only require relationships between certain boundary spanning individuals, others need group- or organization-level social capital to enable collaboration in teams. One can distinguish between three components of social capital: (1) relational capital (trust, identification and obligation), (2) cognitive capital (shared ambition, vision, and values) and (3) structural capital (strength and number of ties between actors). Each dimension relates to a specific and identifiable aspect of social capital (Nahapiet and Ghoshal, 1998). In the context of this study, I am specifically concerned with the relational dimension of social capital. While the explanatory power of social capital theory and the central value and importance of social capital to organizations have been popularized within the management literature (e.g., Adler and Kwon, 2002; Lin, 2001; Nahapiet and Ghoshal, 1998; Tsai and Ghoshal, 1998), social capital theory is particularly applicable to better understanding buyer–supplier relationships. First, social capital has been described as the ‘‘relational glue’’ underpinning effective supply chains (McGrath and Sparks, 2005). Second, social capital theory acknowledges that buyer–supplier relationships are embedded within a larger social, environmental, political, and legal context (Håkansson, 1982). Third, social capital enhances the efficiency of buyer–supplier relationships resulting in the creation of opportunities that may not otherwise have been possible (Cousins et al., 2006; Krause et al., 2007; Lawson et al., 2008). Historically, it has been common to look at the transactional nature of buyer–supplier exchanges, masking the embedded social and behavioral aspects. However, just recently social capital has received increasing attention as a theoretical lens through which to understand buyer–supplier relationships and the value creation process—resulting in four articles: drawing on social capital as theoretical underpinning, Cousins et al. (2006) studied inter-organizational socialization processes that create relational value in supply chains. Through case studies with six firms from the European food industry, Knoppen and Christiaanse (2007) investigated the behavioral dimensions of inter-organizational adaptation in buyer– supplier relationships along the lines of social capital theory and delineated adaptation into a cognitive, relational, and structural dimension. Krause et al. (2007) used social capital theory as the explanatory framework for the relationship between buying firms’ supplier development efforts, the accumulation of three types of social capital, and buying firm performance. Lawson et al. (2008) draw on social capital theory to support their model linking relational embeddedness and structural embeddedness to buyer performance improvements within strategic buyer–supplier relationships. Only two of the studies refer briefly to the time contingent value of social capital. To capture relational capital, Krause et al. (2007) included relationship length (i.e., years of the buyer–supplier relationship) as a measure and suggested a simple positive linear relationship between relationship length and improvement in the buying firm’s performance. Knoppen and Christiaanse (2007) were aware that the relationship stage has an influence on interorganizational adaptation. However, the authors did neither investigate the influence of relationship length nor relationshiplife cycle in much detail. They merely concluded from their case studies that ‘‘[p]artners admitted that trust had grown over the years, by living through good and bad times together.’’ (Knoppen and Christiaanse, 2007, p. 217) The authors realized that the crosssectional assessment of inter-organizational adaptation is a limitation and that future research should ideally apply a longitudinal approach. Both studies did not capture path dependence in the evolution of social capital. Krause et al. (2007, p. 534) pointed out in the discussion of relational capital that ‘‘past transactions may alter the calculus for further transactions’’ and that ‘‘prior history of cooperation between firms’’ has an impact on buyer–supplier relationship outcomes. However, the authors did not factor the path dependence of buyer–supplier relationships into their model. Path dependence could have been modeled by including some measure of relationship length or relationship life-cycle as a moderator between a buyer–supplier relationship management practice and performance. In a nutshell, I suggest to account for the dynamic nature of buyer–supplier relationships over the relationship life-cycle in studies on supplier development. 2.2. Dynamic nature of buyer–supplier relationships Krause et al. (2007) posited simple positive linear relationships between relationship length and the improvement in two categories of buying firm performance. Both relationships were not supported, which is not surprising given the recent hints of social capital theorists to the path dependence of social capital. Kotabe et al. (2003) studied two forms of knowledge exchange between a buying firm and a supplier – which can be considered as S.M. Wagner / Int. J. Production Economics 129 (2011) 277–283 a means of supplier development (Krause et al., 2000; Wagner, 2006) – and its impact on supplier performance and included the length of the relationship as a moderator. The results show that the hypotheses were only partially supported: relationship length did not moderate the link between technical exchanges and supplier performance improvements, while relationship length did moderate the link between efforts to transfer technology and supplier performance improvements. These findings caused them to argue that simple technical exchanges can enhance supplier performance independent of the history of the relationship. I argue that a more accurate model of supplier development activities should account for the life-cycle of the buyer–supplier relationship by including a squared term for relationship length as a moderator for the relationship between the buying firm’s supplier development activities and the improvement in the buying firm’s performance. The inclusion of a squared term for relationship length as a moderator is a much better reflection of the dynamic nature of buyer–supplier relationships over the relationship lifecycle. Fig. 1 depicts the possible approaches to include relationship length in a model on supplier development. The marketing literature emphasizes the importance of the dynamic nature of buyer–supplier relationships and encourages researchers to include the relationship life-cycle in their analysis. Several marketing scholars insist that the interactions between buyers and suppliers and their outcomes are contingent on the stage of the buyer–supplier relationship (e.g., Dwyer et al., 1987; Frazier et al., 1988; Jap and Ganesan, 2000; Medlin, 2004; Wilson, 1995). Researchers have proposed several ways of categorizing the phases in the buyer–supplier relationship. Aside from the number of phases and their labels, in all relationship models the phases are characterized by their direction and strength of growth (e.g., initiation, maturity, and decline). Buyer–supplier relationships are built up over time through legal, formal and informal exchange processes, and relation-specific investments (Ring and Van De Ven, 1994). The relationship life-cycle influences the development of central relationship marketing constructs, such as cooperation, adaptation, information sharing, or Source 279 commitment (Jap and Ganesan, 2000; Wilson, 1995). Supplier development will be more successful if the relationship is in a stage where the levels of cooperation, adaptation, information sharing, commitment, etc. are high (maturity) rather than low (initiation and decline). Trust is a central organizing construct in buyer–supplier relationships. Trust builds slowly from experience as the relationship progresses and vanishes as the firms seek to leave the relationship (Dwyer et al., 1987; Zaheer et al., 1998). Firms in buyer–supplier relationships are more willing to work with other firms they can trust. When trust prevails, employees involved in supplier development activities will be more open to knowledge sharing with employees of the other party. Therefore, the outcome of supplier development activities in trust-based and reliable relationships will be more positive. The low impact of supplier development at the early and late stages and the high impact at the intermediate stages of the buyer– supplier relationship life-cycle are also supported by research of Jap and Anderson (2007). They found that relationship properties – such as goal congruence, idiosyncratic time investments, idiosyncratic adaptation investments, willingness to take risk, or information exchange – are low in the exploration and decline phases of the relationship and high in the build-up and maturity phases. The effectiveness of supplier development activities will follow such a pattern of increase, zenith, and decline because many of these relationship properties are supportive or necessary for supplier development activities. In sum, in established buyer–supplier relationships, a buying firm’s supplier development activities will have the highest impact on its performance improvement. In contrast, supplier development in newer and older buyer–supplier relationships will be detrimental to the buying firm’s performance. As a refinement and extension of the work of Krause et al. (2007) and Kotabe et al. (2003) I therefore posit: Hypothesis. The linear relationship between supplier development and performance is maximized at a moderate level of Proposed relationship Model P Proposed by Krause, Handfield, and Tyler (2007) Supplier development Performance Relationship length RL P Proposed by Kotabe, Martin, and Domoto (2003) High SD Relationship length Supplier development Performance Low SD RL P Relationship length 2 High SD Proposed in this research Supplier development Performance Low SD RL: Relationship length; P: Performance; SD: Supplier development Fig. 1. Approaches to include relationship length in a model on supplier development. RL 280 S.M. Wagner / Int. J. Production Economics 129 (2011) 277–283 relationship length. Low and high levels of relationship length have a detrimental effect. 3. Methods 3.1. Data collection and sample To test this hypothesis, data were collected through a survey, which was administered to 251 firms in Germany, Switzerland, and Austria. From these 251 targeted firms, the responses of 60 were finally used for this study, yielding an effective response rate of 23.9%. A variety of industries is represented in the sample, including high-tech, automotive, machinery and plant construction, construction, chemicals and pharmaceuticals, food, and textiles. About 30.9% of the responding firms had an annual sales volume of US $100 million or less, 18.2% had between US $100 million and US $250 million, 21.8% between US $250 million and US $ 1 billion, 21.8% between US $1 billion and US $5 billion, and 7.3% of more than US $5 billion. The average annual sales volume was US $1.56 billion. Purchasing or supply chain management executives were the key informants. These informants are likely to have an overarching, boundary-spanning view of their companies’ supplier development activities (Jemison, 1984). The majority of informants in this sample were heads of purchasing (61.7%) and heads of supply chain management, logistics or materials management (20.0%). The remainder described themselves as purchasing or commodity managers (11.7%), heads of supplier development, procurement information managers, or quality managers (6.7%). All had held their position for an average of 5.3 years and had been with the firm for an average of 7.0 years. The respondents were asked to answer the questions with respect to the development of one particular supplier. Therefore, the units of analysis in this research are not the buying firms’ supplier development activities in general, but rather the activities performed and the performance improvements achieved through the development of an individual supplier (‘‘Supplier X’’). On average, the firms have maintained relationships with the suppliers for about 10.2 years prior to their development, which ranged from 1 to 22 years. Furthermore, from the total of 60 supplier development incidents in my sample, 50 pertain to suppliers of products, such as printed circuit boards, electronic assemblies, mobile phone handsets, plastics moldings, hydraulic power units, chemicals, flavoring, or tomato puree. The remaining ten were suppliers of services, such as logistics services, mechanical processing, electric installation, or facility management. As can be seen, the supplier development activities included in this study cover a broad spectrum of products and services, thus enhancing the robustness and generalizability of the results. 3.2. Measures The measures used in my study tie in with the measures used by Krause et al. (2007). Multiple-item measures assess the two main constructs on five-point Likert scales. Translated descriptions of the specific measures and items used are included in Appendix A. Descriptive statistics, correlations of summated composites, and scale reliabilities are summarized in Table 1. Supplier development can be categorized as either ‘‘indirect’’ (also called ‘‘externalized’’) or ‘‘direct’’ (also called ‘‘internalized’’). When a buying firm engages in indirect supplier development, the firm commits no or only limited resources to a specific supplier. In case of direct supplier development, the buying firm plays an active role and dedicates considerable relation-specific resources to a supplier (Krause et al., 2000; Monczka et al., 1993). The supplier development construct used in this study consists of direct supplier development activities. There are two reasons why my supplier development measure taps direct supplier development activities. First, strategic buyer–supplier relationships and social capital accumulation are more relevant for direct supplier development than for indirect supplier development. Second, Kotabe et al.’s (2003) and Krause et al.’s (2007) supplier development construct also pertains to direct supplier development activities. The five items were selected from prior studies, which have assigned a range of activities to direct development (Krause et al., 2000; Wagner, 2006). Thus, the measures used for supplier development focus on the allocation of buyer personnel to the supplier and the transfer of tacit knowledge in order to improve the supplier’s skill base with respect to technology, product development and manufacturing, and training of supplier personnel. The supplier development scale shows a satisfactory level of reliability with a Cronbach’s alpha of 0.81. To capture the impact of the supplier development activities on the buying firm’s performance improvement I developed a sevenitem scale based on prevailing supplier performance goals, and competitive priorities in operations, supply chain management, and purchasing (Krause et al., 2001; Ward et al., 1998) as well as on the operationalization of Krause et al. (2007) ‘‘quality, delivery, and flexibility’’ performance improvement construct. The items indicate the effect of the supplier development activities on the buying firm’s own product and service performance. The performance improvement construct turned out to be reliable with a favorable Cronbach’s alpha of 0.90. To ensure discriminant validity, principal component factor analysis (as shown in Appendix A) was conducted. The analysis resulted in two uniquely interpretable factors, with all supplier development items clearly loading together on one factor, and all performance improvement items loading together on another factor. The explained variance of these two factors was 61%. To capture the dynamics of a buyer–supplier relationship over the life-cycle would require the collection of longitudinal data on the relationship over several years. Since such longitudinal studies are very difficult to perform, researchers typically examine buyer– supplier relationships at a single point in time. To overcome this challenge one can classify the relationships by their phase and use this information for quasi-longitudinal analysis (Anderson, 1995). Table 1 Descriptive statistics and correlations. Variable Items Scale Alpha Mean S.D. (1) (2) (3) (4) (5) (1) (2) (3) (4) (5) 1 1 5 1 7 US $ 5-point 5-point Years 5-point – – 0.81 – 0.90 1.56 bn 3.82 2.63 10.2 3.53 4.14 bn 1.24 1.03 5.9 1.06 1.00 0.04 0.26* 0.03 0.11 1.00 0.03 0.13 0.32** 1.00 0.02 0.30** 1.00 0.15 1.00 Annual sales Strategic importance Supplier development Relationship length Performance improvement Notes: N ¼60. n Correlation significant at the 0.10 level. Correlation significant at the 0.05 level. nn S.M. Wagner / Int. J. Production Economics 129 (2011) 277–283 In my study, I applied the squared term for relationship length as a proxy for the relationship life-cycle stage. In order to eliminate undesired sources of variance that confound research findings, two control variables were included in the analysis. First, since the financial resources of larger firms could make them more successful in their supplier development activities, firm size can be a potential source of variance. Therefore, I included firm size – measured by a single item asking respondents for their firms’ annual sales volume in US dollars – as control variable in my analysis when I tested the effect of supplier development activities on supplier firm improvements. Second, since buying firms might pay particular attention to suppliers of strategic items and initiate supplier development in different situations (e.g., even in case of minor supplier deficiencies) and support supplier development activities more intensively (as opposed to suppliers of non-strategic items), another control variable was included. The respondents had to indicate in a single item to which degree the ‘‘delivery of Supplier X was of strategic importance for my firm.’’ 281 the linear by curvilinear interaction by including the product of supplier development and the squared term for relationship length. To support the linear by curvilinear interaction, the standard estimate should be negative and significant, with a significant change in the model’s explained variance. The results in Model 3 in Table 2 support my hypothesis (b¼ 1.91, po0.05) and show that the degree of linearity of the relationship of supplier development to performance improvement depends curvilinearly upon relationship length. This relationship is depicted in Fig. 2 for medium (mean), low ( 1 standard deviation) and high (+ 1 standard deviation) levels of supplier development. Upon entering the linear by curvilinear interaction term, the overall model is highly significant (p o0.01), and the explained variance increases by 0.07 (p o0.05). 5. Discussion and managerial implications The analysis presented in this article refines and extends previous work on the performance implications of supplier Following the procedure proposed by Cohen et al. (2003, pp. 292–295) and Jaccard and Turrisi (2003, pp. 60–65) I employed hierarchical regression analysis and estimated three models in order to test my research hypothesis that a linear by curvilinear interaction exists among supplier development, relationship length, and performance improvement. Since interactions are involved, the variables were standardized prior to the analysis (Bauer and Curran, 2005; Cohen et al., 2003). Table 2 presents the standardized parameter estimates and t-values resulting from these models. Model 1 – the baseline model – includes the control variables and is significant (p o0.05). The strategic importance of the purchased item is significantly related to performance improvement (b¼0.32, po0.05). Model 2 estimates the main and linear interaction effects of the buying firm’s supplier development activities and relationship length. Supplier development is significantly related to performance improvement (b¼ 0.35, p o0.05). Relationship length in itself is not related to performance improvement. The overall model is significant (p o0.05). In Model 3 I tested Performance improvement 4. Analysis and results High Medium Low Relationship length Fig. 2. Performance improvements depending on relationship length at different levels of supplier development. Table 2 Regression analysis. Independent variables Controls Annual sales Strategic importance Model 1 Model 2 b t-value b t-value b t-value 0.12 0.32nn 0.91 2.38 0.19 0.28nn 1.39 2.17 0.28nn 0.30nn 2.06 2.36 0.35nn 0.07 0.06 0.14 2.62 0.13 0.11 1.07 1.70nn 0.07 0.19 1.14n 2.61 0.14 0.36 1.84 1.91nn 2.11 Lower order components Supplier development Relationship length Relationship length2 Supplier development Relationship length Linear by curvilinear component Supplier development Relationship length2 R2 R2 change F n 0.10. 0.05. nnn 0.01. nn Model 3 0.11 0.11nn 3.17nn 0.26 0.15n 2.63nn 0.33 0.07nn 3.07nnn 282 S.M. Wagner / Int. J. Production Economics 129 (2011) 277–283 development by supporting my hypothesis that the linear relationship between supplier development and performance is maximized at intermediate relationship life-cycle stages. As such, drawing on social capital theory and the relationship marketing literature, I show that neither relationship length as a direct antecedent of performance (Krause et al., 2007) nor as a moderator in the link between supplier development and performance (Kotabe et al., 2003) account sufficiently for the dynamics of buyer–supplier relationships (Dwyer et al., 1987) and the path dependence of social capital evolution (Rhee, 2007). Instead, given that I used the squared term of relationship length as a proxy for the life-cycle of the buyer–supplier relationship I show that the effectiveness of a buying firm’s supplier development activities is moderated by the relationship life-cycle. Using the relationship life-cycle as a moderator, I account for the fact that for supplier development to be successful, established and partnership-like buyer–supplier relationships are required (Araz and Ozkarahan, 2007; Talluri and Narasimhan, 2004). Critical constituent and building-blocks of supplier development are trust, communication and information exchange, and relation-specific investments (time, resources, know-how). In buyer–supplier relationships, establishing trust, strong communication and information links, and building up relation-specific assets is time bound (Fichman and Levinthal, 1991; Jap and Anderson, 2007; Kogut and Zander, 1992). In an initial acquaintance phase (initiation phase), the buyer and supplier develop relation-specific routines so that they are better able to engage in supplier development activities (e.g., exchange of tacit knowledge) (Dwyer et al., 1987; Ring and Van De Ven, 1994). When a buyer–supplier relationship is in the decline phase (e.g., due to a discomfort, discontent or disagreement about the collaboration, or simply because of the phase-out of a product sourced from the supplier) and approaches the termination of the relationship, both parties will engage less in relationspecific routine and reduce relation-specific investments. That is, the critical constitutes of supplier development vanish and supplier development will become less effective (Dwyer et al., 1987; Ring and Van De Ven, 1994). My study has several important implications for managerial practice. First, prior to investing in supplier development activities, the buying firm should carefully assess the status of the buyer– supplier relationship, because the effectiveness of supplier development depends on the life-cycle (e.g., initiation, maturity, or decline) of the buyer–supplier relationship. Second, the buying firm should stay away from direct supplier development (which I investigate in the present study) in the very early and very late stages of the relationship with a supplier. My life-cycle perspective confirms previous recommendations that direct supplier development activities should be preceded by indirect supplier development activities (Giunipero, 1990; Krause et al., 2000; Wagner, 2006). That is, in the early stage of a buyer–supplier relationship the buying firm should consider indirect supplier development (e.g., supplier assessment, evaluation, or feedback) and then gradually move into direct development activities (e.g., training, consulting, or staff transfer). On the contrary, in declining buyer– supplier relationships the buying firm should gradually move from direct to indirect development activities. 6. Methodological implications and recommendations From my research I can draw some valuable implications and recommendations for future studies. First, I show that it is vital to account properly for the path dependence in the evolution of social capital and the theoretically well-established dynamic nature of buyer–supplier relationships in studies on supplier development, because the relationship life-cycle might moderate the relationship between supplier relationship management practices and performance outcomes. Second, the quasi-longitudinal study design put forward in this research is a useful way to account for the dynamics of buyer–supplier relationships in light of the resource and time constraints of academic research. Third, by having used the squared term for relationship length as a proxy for relationship life-cycle stage I want to point out that a curvilinear interaction effect of relationship length is equivalent to a linear interaction effect of relationship life-cycle. As a consequence, future research could either use objective measures of relationship length or subjective measures of relationship life-cycle in order to account for the dynamic nature of the buyer–supplier relationship in studies on supplier development practices and its effects on performance. Both measures have their strengths and shortcomings. While researchers might obtain objective relationship length measures from a second data source (e.g., a firm’s ERP system), thus reducing the threat of common source bias, such data might not be available. A subjective assessment of the relationship life-cycle can be obtained by collecting information about the strength and direction of growth. More specifically, measuring the intention to expand the business with a supplier (e.g., the purchasing volume with a supplier) can serve as a reverse coded proxy for the maturity of the buyer–supplier relationship. A high intention to expand business with a supplier would indicate a buyer–supplier relationship in its initiation phase, a low intention to expand business with a supplier would indicate a mature relationship, and the intention to reduce business would indicate a declining buyer–supplier relationship. I hope that my findings will encourage other scholars in production and operations management to embark on research into the life-cycle of buyer–supplier relationships. Appendix A See Table A1. Table A1 Exploratory factor analysis. Survey items Supplier Performance development improvement Our firm has undertaken supplier development Giving manufacturing related advice (e.g., processes, machining process, machine set up). Training of employees from Supplier X. Giving product development related advice (e.g., processes, project management). The transfer of employees to Supplier X. Giving technological advice (e.g., materials, software). with Supplier X through y 0.800 0.097 0.793 0.718 0.003 0.202 0.699 0.690 0.080 0.128 Through the development of Supplier X our firm was able to y Improve our delivery reliability. 0.076 0.847 Reduce time-to-market. 0.017 0.843 Reduce production downtimes. 0.349 0.782 Increase the satisfaction of our customers. 0.162 0.773 Improve the reliability of our products. 0.188 0.733 Improve the quality of our products. 0.292 0.724 Offer more innovative products to our 0.033 0.721 customers. Notes: All items were measured on five-point Likert scales ranging from 1 (‘‘strongly disagree’’) to 5 (‘‘strongly agree’’). S.M. Wagner / Int. J. Production Economics 129 (2011) 277–283 References Adler, P.S., Kwon, S.-W., 2002. Social capital: prospects for a new concept. Academy of Management Review 27 (1), 17–40. Anderson, J.C., 1995. Relationships in business markets: exchange episodes, value creation, and their empirical assessment. 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