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Consistency and Transformation in the Quality Movement. Su Mi Dahlgaard-Park
Introduction
Two currently "hot" process improvement approaches are six sigma and lean enterprise theory. The two are related, but distinct. Six sigma focuses on the reduction and removal of variation by the application of an extensive set of statistical tools and supporting software, whilst lean thinking focuses on the reduction and removal of waste by process and value analysis. Both methods have origins in aspects of Japanese improvement practise, but have been to a large extend molded in North America. An area of overlap in Poka Yoke/mistake proofing since human errors cause both unwanted variation and waste. Lean manufacturing, now extended to lean service originated in Japan in Toyota. In contrast, six sigma is an America packaging of a statistical approach widely used in Japanese industry.
There have been attempts to combine the two methodologies under titles such as "Lean Six Sigma" or "Lean Sigma". Often, this alleged combination is no more than a "philosophical" or near-religious argument about professed compatibility of approaches. In reality these are practical examples of incompatibility and even conflicts between the approaches that have lead to suboptimal processes and process improvement programmes. To what extent then are the two approaches compatible and how can they be effectively combined in one system?
This paper reviews the origins and nature of the six sigma and lean approaches to process improvement, identifying their individual and joint strengths and limitations. A comparison is made of the two approaches and of the argument for and against combination discussed. The basis for compatibility is assessed and holistic approach to combination into a six sigma - lean methodology is proposed.
The six sigma approach
The professional and academic management and engineering press has been giving increasing attention to six sigma. [1] Bendell (2000) reviewed the origins of the six sigma approach. [5] Bendell and Marra (2002) analysed the method, [4] Bendell and Corke (2001) amongst others focussed on particular deficiencies and criticisms of the approach, and [2] Bendell (2002a) considered whether application in Europe was qualitatively different. Originating in Motorola and highly developed within GE and many others, the application has now spread across manufacturing, design and transactional areas. See, e.g. [7] Harry and Schroeder (2000) and...