Six Sigma vs. Design for Six Sigma : selection of the requisite Six Sigma approach using multi-criteria decision analysis : innovation report

摘要

The literature suggests that organisations which have adopted Six Sigma have realised that upon achieving a Five Sigma level the only way to surpass this is to redesign the process(es) by means of Design for Six Sigma (DFSS). For others, the selection of Six Sigma over the DFSS approach is not a definitive question and just a guideline can be provided. A major objective of this research was to extend the selection of the requisite Six Sigma approach beyond the sigma level case and the general guidelines, towards a multi-criteria decision using established techniques. Thus, two research questions were defined: what influences the selection of the requisite Six Sigma approach, i. e. Six Sigma versus DFSS? and, how effective is the use of Multi-Criteria Decision Analysis (MCDA) techniques in the selection of the requisite Six Sigma approach? An action research methodology was applied where one Six Sigma project, one DFSS project and one Six Sigma project applied in a non-manufacturing process were implemented and analysed in collaboration with 3M Corporation, General Domestic Appliances (GDA) and Land Rover. From the action research spiral it was concluded that the sigma level has a positive association with the selection of redesign or improvement efforts within Six Sigma, however the Five Sigma level cannot necessarily dictate the use of one approach over the other. Besides the sigma level the selection of the requisite Six Sigma approach is influenced by multiple and conflicting criteria. In addition, the selection can occur at different stages of the methodologies. To assist decision-makers in organising, synthesising and optimising the criteria affecting this decision, the Stochastic Analytic Hierarchy Process (SAHP) was developed and applied to the problem at hand. The SAHP was developed on the basis of Analytic Hierarchy Process (AHP) and disparate sources of relevant literature. SAHP provides a mechanism for achieving a more effective selection of the requisite Six Sigma approach in the form of considering multiple and conflicting criteria using quantitative and qualitative information under uncertainty. In contrast to the traditional AHP, SAHP incorporates probabilistic distributions to incorporate uncertainty that people have in converging into a Likert scale their judgments of preferences. The vector of priorities is calculated using Monte Carlo simulation and the final rankings analysed for rank reversal using statistical analysis with managerial aspects introduced systematically. The concept and implementation of SAHP is new to the selection of the requisite Six Sigma approach and as such it constitutes the main innovation to result from this research. It extends the selection of the requisite Six Sigma approach towards a systematic multi-criteria decision considering multiple and conflicting criteria under uncertainty. Furthermore, while SAHP was originally conceived as a specific aid to the improve or redesign issue within Six Sigma, this research indicates that it is potentially much more widely applicable. This research also provides evidence of how different factors affecting the selection of requisite Six Sigma approach were considered. Further areas of research include the use of a positivist method in order to increase the sample size of the research and identify different factors affecting the decision improve or redesign. The development of SAHP software and extending the SAHP practice to different multi-criteria decisions are also potential areas for further research.