تئوری در حال تکامل مدیریت کیفیت: نقش شش سیگما

While Six Sigma is increasingly implemented in industry, little academic research has been done on Six Sigma and its influence on quality management theory and application. There is a criticism that Six Sigma simply puts traditional quality management practices in a new package. To investigate this issue and the role of Six Sigma in quality management, this study reviewed both the traditional quality management and Six Sigma literatures and identified three new practices that are critical for implementing Six Sigma's concept and method in an organization. These practices are referred to as: Six Sigma role structure, Six Sigma structured improvement procedure, and Six Sigma focus on metrics. A research model and survey instrument were developed to investigate how these Six Sigma practices integrate with seven traditional quality management practices to affect quality performance and business performance. Test results based on a sample of 226 US manufacturing plants revealed that the three Six Sigma practices are distinct practices from traditional quality management practices, and that they complement the traditional quality management practices in improving performance. The implications of the findings for researchers and practitioners are discussed and further research directions are offered.

Quality management (QM) has developed into a mature field with sound definitional and conceptual foundations (Sousa and Voss, 2002), but new QM methods continue to grow. For example, Six Sigma, which is “an organized and systematic method for strategic process improvement and new product and service development that relies on statistical methods and the scientific method to make dramatic reductions in customer defined defect rates” (Linderman et al., 2003, p. 194), generates intense interest in industry. Since its initiation at Motorola in the 1980s, many companies including GE, Honeywell, Sony, Caterpillar, and Johnson Controls have adopted Six Sigma and obtained substantial benefits (Pande et al., 2000 and Snee and Hoerl, 2003). However, Six Sigma is criticized as offering nothing new and simply repackaging traditional QM practices (Clifford, 2001, Dalgleish, 2003 and Stamatis, 2000). It is argued that the large returns from Six Sigma at some companies were due to the initial quality level of these companies being so low that anything would have drastically improved their quality (Stamatis, 2000). Although there have been numerous case studies, comprehensive discussions, books and websites addressing Six Sigma, very little scholarly research has been done on Six Sigma and its influence on quality management theory and application (Goffnett, 2004 and Schroeder et al., 2005). This study explores what is new in Six Sigma by identifying the practices that are critical for implementing Six Sigma's concept and method in an organization. It then develops a model of how the Six Sigma practices integrate with traditional QM practices to improve performance. The model was tested using survey data collected from 226 manufacturing plants in the US. The empirical findings of this study strengthen our understanding of Six Sigma's key practices and how it complements traditional QM, and provide practitioners with rigorous research-based answers about Six Sigma implementation.

4.1. Theoretical implications This study identified three new Six Sigma practices – the Six Sigma role structure, the Six Sigma structured improvement procedure, and the Six Sigma focus on metrics – and developed a model to investigate how these Six Sigma practices integrate with seven traditional QM practices. The findings of this study suggest a synergy between the Six Sigma practices and traditional QM practices in improving quality performance. This corroborates the view that QM practices work as an integrated, interdependent system to achieve competitive advantage (e.g., Flynn et al., 1995, Kaynak, 2003 and Yeung et al., 2005). The structural model suggests important paths by which the Six Sigma practices and traditional QM practices complement each other in improving performance as discussed below. The QM literature has unanimously emphasized the importance of top management support for QM (Beer, 2003 and Yeung et al., 2005). This study once again confirms that top management support is critical for traditional QM and it is also important for Six Sigma. Top management support directly supports the Six Sigma role structure and the Six Sigma focus on metrics as well as three traditional QM infrastructure practices. The success of executing substantial changes required for Six Sigma deployment relies on whether top management understands and accepts Six Sigma principles and whether they are willing to support and enable the restructuring of the organization's policies (Antony and Banuelas, 2002 and Lee and Choi, 2006). The Six Sigma role structure's support for workforce management is a significant finding. It suggests the potential of using Six Sigma to enhance traditional human resource management practices, particularly in the areas of human resource planning and management, training, and employee recognition. Employee selection has received little attention in QM research (Dean and Bowen, 1994), however selection and planning of employees, especially leaders, for continuous improvement is critical for companies to achieve competitive advantage (Schroeder et al., 2005). Establishment of the Six Sigma role structure assists firms in recruiting the right people with the requisite technical skills and personality traits, and then developing them with training and deploying them in leadership roles with executive coaching to enhance their chances of success in quality improvement. The black and green belt system is used as a vehicle to develop the future leaders in some firms (Schroeder et al., 2005). The Six Sigma specialists have an organization-wide view of continuous improvement and an in-depth knowledge of the business processes and QM tools and methods. Such human resource is rare and difficult to imitate and thus is a critical resource for the firm to achieve sustainable competitive advantage (Barney and Wright, 1998, Gowen and Tallon, 2005 and Saá-Pérez and García-Falcón, 2002). The Six Sigma role structure also supports the structured improvement procedure. And, indirectly, through its influence on workforce management and the Six Sigma structured procedure, the Six Sigma role structure affects all three traditional QM core practices and the practice of the Six Sigma focus on metrics as well. This supports the argument that not only does Six Sigma receive support from traditional QM practices, but also it adds a new element to the QM infrastructure. This study found that customer relationship directly affects quality information, and supplier relationship directly affects product/service design and process management. The significant relationships between these practices are consistent with the findings of prior studies such as Forza and Flippini (1998), Kaynak (2003), and Mohrman et al. (1995). Quality information is then found to have direct effects on supplier relationship and Six Sigma focus on metrics. These findings indicate that cooperation with external customers and suppliers continues to be very important, even with Six Sigma. Firms that focus on satisfying their customers’ needs and expectations are able to collect comprehensive, accurate and timely information and use the information to generate appropriate performance measures and in working with their suppliers in product design and process improvement. Neither quality information nor the Six Sigma structured improvement procedure has a direct effect on product/service design or process management, but those two practices are found to have a significant effect on the Six Sigma focus on metric which in turn directly affects product/service design and process management. Therefore, at the level of core practices, the Six Sigma focus on metrics mediates the effects of quality information and structured procedure on product/service design and process management. This finding highlights the importance of data and objective measurement in quality improvement. It is important to gather quality information, but this information needs to be gathered and used within an environment that values the use of objective metrics. Using the Six Sigma structured procedure ensures that teams use data and metrics during the process of solving quality problems. Moreover, such integration of Six Sigma core and traditional QM core practices corroborates the important role of goals (which is defined by various Six Sigma metrics) in continuous improvement as promoted by Linderman et al., 2003 and Linderman et al., 2006. Linderman et al. (2006) found that goals can be effective in Six Sigma improvement projects when the teams adhere to rigorous application of QM tools and method. This study further illustrates that when firms make efforts to collect accurate and timely quality data and apply the structured procedure as the paradigm of conducting improvement projects, they are more likely to better use Six Sigma metrics to monitor and motivate continuous improvement activities, which finally will lead to more effective product/service design and process management practices. Product/service design and process management are shown to be the two practices that directly affect quality performance. This finding reinforces the suggestion by Ahire and Dreyfus (2000) that in order to achieve superior quality outcomes, firms need to balance their design and process management efforts and persevere with the long-term implementation of these efforts. However, unlike studies by Kaynak (2003) and Ahire and Dreyfus (2000), this study did not find support for the direct effect of product/service design on process management. Flynn et al. (1995) suspected that product design process would be significantly related to a measure of the degree of process control present, rather than a measure of the use of process improvement practices. However, our process management scale measured the use of various process improvement practices, which did not reflect the impact of effective design on manufacturability and process stability (Flynn et al., 1995). Additional research examining the influence of design management on process management would be valuable. Overall, the structural model suggests the importance of a sound QM foundation for effective adoption of the new Six Sigma practices in the organization and the potential of implementing the Six Sigma practices to enhance its existing QM system. And, it shows that the Six Sigma practices and traditional QM practices work together to generate improved quality performance, which then leads to higher business performance. While there have been doubts about QM's return on the investment, more recent research found that effective implementation of QM practices will contribute to better financial, marketing, and even innovation performance by improving quality performance and/or operational performance (Kaynak, 2003, Nair, 2006, Prajogo and Sohal, 2003, Sila and Ebrahimpour, 2005, Sousa and Voss, 2002 and Yeung et al., 2005). This study adds to the literature by providing further evidence that investments in QM/Six Sigma benefit an organization's bottom-line by significantly improving product and service quality. 4.2. Managerial implications This study investigates the question about whether Six Sigma is simply a repackaging of traditional QM methods or provides a new approach to improving quality and organizational excellence. This question has created some confusion about Six Sigma (Goffnett, 2004), and also put managers in a dilemma: on one hand, if they do not adopt Six Sigma because it is considered to be the same as traditional QM methods, their company may lose the opportunity to gain substantial benefits as GE and other companies practicing Six Sigma have achieved from their Six Sigma efforts; on the other hand, if Six Sigma is different, there lacks solid answer to what are the new practices that the company needs to implement to improve the current QM system (Schroeder et al., 2008). The empirical findings of this study help to clarify the relationship of Six Sigma and traditional QM. Six Sigma is grown out of traditional QM methods and many traditional QM practices are recognized as important for Six Sigma implementation (Bhote, 2003, Breyfogle et al., 2001, Gale, 2003, Henderson and Evans, 2000, Hendricks and Kelbaugh, 1998, Lee and Choi, 2006, Pyzdek, 2003 and Schroeder et al., 2008). However, Six Sigma does not eliminate the traditional QM practices, nor does it simply repackage them. The conceptual foundation and the empirical evidence included in this study suggest that Six Sigma offers managers three additional practices that augment the traditional QM practices and provide new paths to quality improvement. The three Six Sigma practices identified in this study suggests that the deployment of Six Sigma entails establishing a Six Sigma role structure within the organization's human resource management system, instituting the structured improvement procedure as a formal paradigm of conducting improvement projects, and emphasizing using quantitative objective metrics in quality improvement. Managers can use the scales developed in this study to assess the status of how each of these practice is implemented in their organization. Items in each scale of the Six Sigma practices may be used as a preliminary checklist of the important areas for the managers to address or the goals for the organization to pursue when implementing that practice. The integrated model in this study then reveals some important areas that managers need to consider when they implement the Six Sigma practices in their organization. Top management support directly affects the implementation of Six Sigma role structure and Six Sigma focus on metrics, which suggests that for successful adoption of Six Sigma, it is critical that top management accepts the concept of Six Sigma and is willing to allocate resources to adapt the organizational structure, policies, and processes for Six Sigma. At the level of infrastructure practices, managers may complement the traditional workforce management practice with the Six Sigma role structure to augment their organization's ability in developing employees for continuous improvement. At the level of core practices, it is important to emphasize using the Six Sigma structured improvement procedure and performance metrics to motivate and guide improvement activities in product design and process management with the supply of timely and accurate quality information. 4.3. Limitations This study is subject to several limitations. First, the majority of the data were gathered from a single respondent of each plant, and thus common method variance may be present in the results. Although statistical tests indicated that common method variance does not appear to be a major problem in this study, future work should attempt to gather data from multiple informants to provide a more accurate assessment of construct validity and the relationship of the factors (Ketokivi and Schroeder, 2004), and/or gather objective performance data when possible (Kaynak and Hartley, 2006). Second, considering that the institution of QM practices in an organization is a long-term process, the time-frame for performance measures was set to be 3-years in the questionnaire, but the data showed that while most plants responding in the survey had implemented ISO9000 and/or TQM for more than 3 years, over half of the plants practicing Six Sigma had only implemented it for less than 3 years. While this is not surprising because Six Sigma is a relatively new method, we acknowledge that the outcomes of Six Sigma implementation may not be fully revealed in the reported performance. As Six Sigma gains acceptance in industry, research can further examine the influence of Six Sigma implementation on performance by obtaining larger samples of firms with more experience on Six Sigma. 4.4. Conclusions and future research Despite the limitations discussed above, this study contributes to the scholarly research beginning to examine Six Sigma. Schroeder et al. (2008) started with a definition of Six Sigma and its underlying theory to argue that although the Six Sigma tools and techniques appear similar to prior QM approaches, Six Sigma provides an organizational structure not previously seen. Schroeder et al. proposed that four relevant constructs or elements of Six Sigma such as parallel-meso structure, improvement specialists, structured method, and performance metrics contribute to Six Sigma's performance. Correspondingly, this study identified three Six Sigma practices which are consistent with three of the four elements suggested by Schroeder et al. (2008). Furthermore, this study used a large-scale survey to test these Six Sigma practices and their relationships with traditional QM practices, and we found empirical support for these Six Sigma constructs and their importance to QM and performance improvement, which can provide a basis for more research on Six Sigma. The implementation of QM in an organization requires two types of decisions: what to do and how to do it (Sousa and Voss, 2002). The findings of this study suggest that Six Sigma implementation requires three key practices to work with other QM practices in order to enhance the organization's ability of improving quality. Further research exploring how these Six Sigma practices are adopted in different organizational contexts is needed, since different organizations have different maturity levels of QM implementation and the strengths and weakness of their existing QM systems vary. It is desirable to explore the critical contextual factors influencing the integration of Six Sigma practices into an organization's existing QM system. Another area suggested for future research is the investigation of how Six Sigma works with other improvement methods such as lean manufacturing. There are common characteristics between lean manufacturing and Six Sigma in reducing waste and improving process (Breyfogle et al., 2001). As mentioned earlier, many plants sampled in this study have implemented lean manufacturing in addition to TQM or Six Sigma. Lean Six Sigma is becoming a new continuous improvement approach in industry (Devane, 2004 and George, 2003). Based on the results of this study, researchers may explore how the QM/Six Sigma practices interact with lean manufacturing practices in creating a unique approach to organizational excellence.