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I need Sigma Levels Explained

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  • #53564

    Spark
    Member

    I will shortly be starting my Six Sigma journey and have decided to map current processes using tools to show “Sigma Levels”.

    Having now done this, Im getting a Sigma Level returned as “4.9”

    Can someone explain is this towards the good or bad level? I have assumed that 6 is the point to strieve for ?

    Also Im confused over the “Shift” aspect of Six Sigma. I have used this in my calculations as the processes being analysed are well established. What question or questions drive whether to include or not to include the “Shift” element ?

    Help greatly appreciated for a newbie

    :)

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    #190697

    Strayer
    Participant

    Philip Crosby and others assert that the goal must be zero defects. If you think 4.9 sigma is good enough then you are saying that your goal is to create 337 defects/million. Why would you want to do that? Since statistics deals with probabilities rather than absolutes our goal is to get very close to zero defects (6 sigma, or 3.4 DPMO)

    Is 4.9 sigma good or bad? Others will certainly disagree but I say that since quality is a measure of how well you meet customer needs and expectations that it depends. If the customer expects zero defects then 4.9 is bad. If he expects less then perfection then it may be acceptable. I wouldn’t go so far as to call that “good” since exceeding customer expectations is worthwhile.

    As for the 1.5 sigma shift, it should only come into play when the defect rate is very high so I wouldn’t worry about it. The reasoning is that high variability implies additional uncertainty and the shift adjusts for that.

    Since you say that you’ve used the shift in your calculations you may be doing more work than necessary. It’s good to know the formulas but few of us actually do the calculations. All you need to do is to count the number of defects and the number of opportunities then lookup the sigma level in a table or enter the numbers into a sigma calculator such as the one on this site’s home page. Doing the calculation yourself is extra work and increases potential error.

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    #190699

    Mikel
    Member

    Sparkd,

    Can you tell us what you counted as defects? A 4.9 seems a bit high to an organization who can’t provide the guidance you are seeking.

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    #190701

    Spark
    Member

    Thanks

    My new process metrics look like this:

    Defects=1
    TOP=1000000
    DPO=0.000001
    DPMO=1
    Shift=0
    Sigma-L=4.75
    Sigma Z.B=4.75

    4.75 relates to 1 defects per million
    where zero defects result in a value 4.83

    Question:
    What does the 4.75 and 4.83 show me ?
    Is 4.75 seen as a high Sigma Score compared to 4.75 for zero defects?

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    #190702

    Mikel
    Member

    You should have told us this was a homework problem.

    Do your own homework.

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