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why 6 sigma

Six Sigma – iSixSigma Forums Old Forums General why 6 sigma

This topic contains 5 replies, has 4 voices, and was last updated by  Cone 18 years, 6 months ago.

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  • #27123

    sundeep
    Member

    why we cannot talk nof 7 sigma or 8 sigma?

    has any one achieved 6 sigma level?

    How to calculate ur existing sigma level

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    #65988

    Cone
    Participant

    Very few have achieved 6 — airline safety is at 6.2 — so the discussion of 7 or 8 is not relevant.

    If you reall want help to calculate your sigma level, send copies of your complete defect data along with supporting info like process maps, parts lists, CTQ’s linked to QFD, …

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    #66018

    Evan
    Participant

    3 sigma is 99.5%, 6 sigma is 99.7%, if 7 or 8…, theoretically you can do with huge cost…

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    #66022

    Joe Perito
    Participant

    Six sigma just happens to be the most convenient number aproximately being the closest to zero PPM. Of course, your quality goal could be anything you want. Not so many years ago plus or minus 3 standard deviation was the standard. Prior to that the most common accepted quality was an AQL of 4%. No, no one has acquired six sigma quality yet. Some companies may have one attribute or parameter operating in the six sigma category, but no one has six sigma accross the board. As for the airlines, why do you rate a human life on the same scale and a paint defect? During my trip to Mexico last week, all four plane flights on the same airline was late in taking off or early on arrival only to sit in the parking lot waiting for the gate to open up. After fifty minutes of waiting, they told us to use the open gate that had been open right next to the plane for fifty minutes. The barbequed chicken hash sandwich made me sick from all the grease in it. (Why would anyone serve a barbequed chicken hash sandwhich?) Is this a six sigma airline?

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    #66024

    Cone
    Participant

    Airlines are only six sigma (actually 6.2) on safety as related to deaths or injury. About 3 sigma on everything else.

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    #66033

    Cone
    Participant

    Joe wrote:

    Six sigma just happens to be the most convenient number aproximately being the closest to zero PPM.

    Gary writes:

    Where in the world do you get this stuff?
    3 sigma is close, 4 is closer, 5 is even closer, 6 is even closer, 7 is yet even closer, …… The idea for Six Sigma comes from the benchmarking of the companies that were kicking Motorola’s butt in the early 80’s and the observation that processes shift (purely empirical, no one had or has a theoretical derivation of the shift or how big it really should be). Looking at the benchmark data and using the shifted tables (1.5 shift), Motorola’s competitors were in the mid 5 sigma range and appeared to be converging on 6 in the near future (okay the Motorola guys were wrong on how quickly someone would get to 6 sigma). I was there, I have the original data.

    Joe wrote:

    Not so many years ago plus or minus 3 standard deviation was the standard.

    Gary writes:

    Not so long ago is now. Go see what they still teach in Engineering and MBA schools. It is still +/- 3.

    Joe wrote:

    Prior to that the most common accepted quality was an AQL of 4%.

    Gary writes:

    ? I have Mechanical engineering handbooks from the late forty’s that define +/- 3. This is the same time period that Dodge Romig and many others were working on their famous tables. I know the history from the earliest journals coming from the predecesors to ASQ from the late forty’s and I know of no one promoting a 4% AQL. Please cite your reference, my references are on file at ASQ in Milwaukee.

    Joe wrote:

    As for the airlines, why do you rate a human life on the same scale and a paint defect? During my trip to Mexico last week, all four plane flights on the same airline was late in taking off or early on arrival only to sit in the parking lot waiting for the gate to open up. After fifty minutes of waiting, they told us to use the open gate that had been open right next to the plane for fifty minutes. The barbequed chicken hash sandwich made me sick from all the grease in it. (Why would anyone serve a barbequed chicken hash sandwhich?) Is this a six sigma airline?

    Gary writes:

    Nice story, remember that anecdotes are not evidence. FMEA is where we differentiate the severity of a defect (human life vs. paint defect for example). In the meantime we collect defect information and report sigma levels (or DPMO or whatever) on the data we have and airline safety is at 6.2% with respect to death and injury. The nic

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