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why the number 6 and nothing else!!!!

Six Sigma – iSixSigma Forums Old Forums General why the number 6 and nothing else!!!!

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  • #40668

    Gopinathan
    Participant

    hi
    i am a newbie to 6sigma.
    i just need to know in simple layman language why is the number 6 in six sigma.how is the shift of 1.5 sigma related.
    also difference in short term and long term sigma.awaiting answers soon.
    thanx and regards
    jayesh john
     

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    #126747

    indresh
    Participant

    Do you go to office each day, ok lets assume that office time is 9:30 and you reach on one day at 9:40, 9:20 etc etc.
    No this shows that there is a process variation that means that you were not able to reach the office exactly day after day at 9:30 sharp.
    If you plot all these points on a graph over a period of time you will have a normal data, that means some of the time you have reached bit late and some time early though the average would be around 9:30. assuming no major delays takes place due to any external factors etc.
    now if you boss says that no coming before 9:15 and not after 9:50, hence you will identify in all days that you have come how many were beyond 9:50 (defects as per boss) as well before 9:15 (defects as per boss)
    with this current data lets assume your average was 9:30 and variation was 5 minutes. hence at 1 sigma you would be take all the time that you have come between 9:25 and 9:35, at 2 sigma at 9:20 and 9:40 and so on. but this shows that at 3 sigma you touch your customer limits hence you are able to put in only 3 standard deviations between mean and customer specifications.
    now when the process is at 6 sigma you are able to fit in 6 standard deviations. at 7 sigma 7 and so on. when you take 100 points you will get only 0.00034 points beyond customer specifications limits when the process of your coming to office is at 6 sigma. on 1 million it becomes 3.4. anything beyond 6 this 3.4 goes in decimals hence we take 6 which is 99.99966% error free closest to zero error, but you may take it forward and have 7 sigma process which will have 1 defect in a billion opportunities and so on and so forth.
    hope this helps
    rgds
     

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