What is Six Sigma?

Beside Lean, Six Sigma counts among the most popular performance improvement approaches. Based (and named) upon statistical data and tools, Six Sigma’s aim is to speak with data and facts. It is the most “scientific” methodology in the Theory of ConstraintsLean – Six Sigma (TLS) trio.

Once thought to replace Lean, Six Sigma rather completes it. Despite a certain overlap, many comparisons try to clearly discriminate what is in the Lean and what in the Six Sigma pigeon holes. The following presentation is a nice summary for both Lean and Six Sigma.


2 thoughts on “What is Six Sigma?

  1. Pingback: What is Six Sigma? | The Lean Revolution

  2. Six Sigma is a management fad based on pure farce. It was created by a psychologist who claimed that all processes shift or drift by +/-1.5 sigma in 24 hours and this claim was based on the height of a stack of discs. (Benderizing) Some simple sums yields the meaningless Six Sigma “metric” of 3.4 dpmo.

    Dr Wheeler, the world’s leading process statistician, calls Six Sigma “goofy”. CBS calls it the most stupid fad of all time.
    “Of the 58 large companies announced Six Sigma programs, 91 percent have trailed the S&P 500 since.”
    A survey by Minitab showed that 80% of Six Sigma projects fail (of those brave enough to admit failure).

    While Mikel Harry claimed to be the creator of Six Sigma, it all started with Mr Bill Smith who is claimed to be the “father” of Six Sigma. He had a single article to which we can refer. Mr Smith’s paper makes a bad start by showing that he does not understand the meaning of a Shewhart Chart (control chart). Mr Smith falls into the old bear trap of thinking it’s a probability chart. Dr Shewhart (Founding member, Fellow and President of the Institute of Mathematical Statistics; Fellow and President of the American Statistical Association), showed brilliance in that his charts do not depend on probability distributions. Most Six Sigma practitioners are totally ignorant of this quality fundamental and have been conned into buying statistical software to massage data before it is charted. Dr Shewhart’s assertion was later proved by Dr Wheeler, (PhD in Statistics), in his book “Normality and the Process Behavior Chart.”
    Mr Smith goes on to talk about casting parts in his workplace. He noted how parts shrink after casting and cooling. Mr Smith says shrinkage can be “up to 15%” in his process. Metallurgists who may be reading this may think Mr Smith’s “15%” is an order of magnitude too large, but hey, anything is possible in Six Sigma fairyland. Mr Smith points out that after cooling, his casting process needs to be manually adjusted to try to bring the cooled part into specification. That is, he manually changes his process after each measurement, to try to achieve a target value after cooling. A sort of control-after-the-event.
    Dr Deming warned against such process “tweaking” because it increases variation. Mr Smith didn’t seem to have been aware of Dr Deming’s advice although he did show much respect for him.
    Not surprisingly, there was a lot of variation in Mr Smith’s components. He had “as much as +/- 1.5 sigma off target”. Some simple sums yielded Six Sigma’s “metric” of 3.4 defects per million. This is the origin of Six Sigma’s ‘six sigma’!
    Mr Smith had a process that was out of control. It had special causes that caused the mean to shift dramatically and unpredictably. The farce of Six Sigma began when it was claimed that all processes in all industries, at all times, behave as Mr Smith’s did and that all processes experience the same lack of control that his did.
    Mr Smith refers to a sidebar signed by the magazine editor, Linda Geppert (now deceased). “Another way to improve yield is to increase the design specification width. This influences the quality of product as much as control of process variation does.” If quality could only be as easy as Mr Smith and Ms Geppert claimed. Don’t bother with variation, just broaden the specification limits!
    Linda’s sidebar also creates the much reproduced picture of three overlapping normal distributions. Linda claims it shows what happens when the mean shifts by +/-1.5 sigma. She claims that a variation “of as much as +/-1.5 sigma is not surprising”. I wonder how surprised Linda would be to learn that there is no limit to how far the mean can shift.
    Psychologist, Mikel Harry continued with a series of ridiculous “proofs” of Mr Smiths out-of-control process. The first was his stack of discs to “prove” that all processes shift/drift by +/- 1.5 sigma in 24 hours. Adding to the farce, Harry commented in one of his justifications: “the shift factor is not a statement of how much processes shift”. Other “proofs” followed, such as the claim that +/-1.5 sigma was the maximum that any process could change of its own accord. All are blatant nonsense.
    So if Six Sigma is utter nonsense, what are we to do? Follow Mr Smith’s advice of course! Mr Smith recommends: “The answer has become Total Quality Management”. After all, Motorola won the Baldrige Award using TQM before they slipped into Six Sigma and the company started its downward spiral. Mr Smith advises following Dr Deming’s principles: “His now famous ‘14 points of management’ when followed, appear to move organizations towards prosperity”. Such a pity his employer didn’t follow his advice.
    The responsibility for buy-in to Six Sigma rests on the shoulders of CEOs. CEOs are easily fooled by fast talking Six Sigma salesmen with hollow hype and outlandish promises. It is CEOs who are responsible for the “58 large companies announced Six Sigma programs, 91 percent have trailed the S&P 500 since”.
    There is nothing wrong with that part of Six Sigma its psychologist progenitor called “80% TQM”. It is the name Six Sigma, its foundations and its off shoots, that are the farce. Normalization, incorrect charting methods, dpmo, Six Sigma tables, defects targets, alienation of employees with belts hierarchies are wrong and/or destructive. While there is nothing inherently wrong with some of the material such as hypothesis testing, it is totally irrelevant to process improvement. Dr Deming pointed out: “Analysis of variance, t- test, confidence intervals, and other statistical techniques taught in the books, however interesting, are inappropriate”. Six Sigma courses are simply padded with such material to justify Six Sigma salesmen’s ridiculously high prices. While hypothesis testing was quite appropriate in Harry’s Psychology 101 class, it has no place in process improvement.
    Harry was totally ignorant about the nature of quality. He claimed that TQM, as recommended by his buddy Bill Smith, “… is a defects-focussed quality improvement initiative.” Unless you have been living on another planet, you will know that TQM is based on “on target with minimum variance”, as described by Dr Deming, Dr Wheeler and Dr Taguchi. It is Harry’s own Six Sigma that is the defects based methodology. It was precisely this reason that Dr Wheeler and Professor Deming stated “Six Sigma, and all other [specification-based] nostrums all miss the point. The sooner one wakes up, the sooner one can begin to compete.”
    Harry make the incredible claim “1.5 sigma shift factor have [sic] little to do with SPC”. It seems Harry missed the point that process improvement is the basis of quality! Harry states: “… opponents of the shift factor are absolutely correct – the shift factor has no place in the world of statistical process control or statistical process monitoring.”
    It is time to throw out Six Sigma and everything related to it. It is time to get back to basics and the fundamentals of quality. “Institute a vigorous program of education and self-improvement for everyone” (point 13 of Dr Deming’s 14 points). All employees have a role to play in quality, not just the privileged.
    My papers give more details:


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