<P> One criticism voiced by Yasar Jarrar and Andy Neely from the Cranfield School of Management's Centre for Business Performance is that while Six Sigma is a powerful approach, it can also unduly dominate an organization's culture; and they add that much of the Six Sigma literature--in a remarkable way (six - sigma claims to be evidence, scientifically based)--lacks academic rigor: </P> <P> One final criticism, probably more to the Six Sigma literature than concepts, relates to the evidence for Six Sigma's success . So far, documented case studies using the Six Sigma methods are presented as the strongest evidence for its success . However, looking at these documented cases, and apart from a few that are detailed from the experience of leading organizations like GE and Motorola, most cases are not documented in a systemic or academic manner . In fact, the majority are case studies illustrated on websites, and are, at best, sketchy . They provide no mention of any specific Six Sigma methods that were used to resolve the problems . It has been argued that by relying on the Six Sigma criteria, management is lulled into the idea that something is being done about quality, whereas any resulting improvement is accidental (Latzko 1995). Thus, when looking at the evidence put forward for Six Sigma success, mostly by consultants and people with vested interests, the question that begs to be asked is: are we making a true improvement with Six Sigma methods or just getting skilled at telling stories? Everyone seems to believe that we are making true improvements, but there is some way to go to document these empirically and clarify the causal relations . </P> <P> The statistician Donald J. Wheeler has dismissed the 1.5 sigma shift as "goofy" because of its arbitrary nature . Its universal applicability is seen as doubtful . </P> <P> The 1.5 sigma shift has also become contentious because it results in stated "sigma levels" that reflect short - term rather than long - term performance: a process that has long - term defect levels corresponding to 4.5 sigma performance is, by Six Sigma convention, described as a "six sigma process ." The accepted Six Sigma scoring system thus cannot be equated to actual normal distribution probabilities for the stated number of standard deviations, and this has been a key bone of contention over how Six Sigma measures are defined . The fact that it is rarely explained that a "6 sigma" process will have long - term defect rates corresponding to 4.5 sigma performance rather than actual 6 sigma performance has led several commentators to express the opinion that Six Sigma is a confidence trick . </P>

What is a six sigma green belt certification