Problem with Calculating Sigma Level with Qualitative Output Results

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This topic contains 3 replies, has 2 voices, and was last updated by  sheraz 1 year, 1 month ago.

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    hi there, there is knitting process of socks, 100% inspection is conducted by operators by themselves, they segregate bad units from goon ones. total defective opportunities/ unit is 11.not measuring many defects per unit (one defect found, rejected)now
    total units produced and inspected are = 45300
    total defective units = 3230
    defective opportunities/unit = 11
    by calculation DPMO is 6482 (3.9 sigma )
    how can it possible with 7% defective rate………..
    plz i need help, many thanks in anticipation


    Chris Seider

    Sigma level of the process is used to compare differing complexities of processes and help prioritize from an upper level. DPMO is a different measurement than ppm defective.

    Did you use normsinv in excel? Careful of shifted tables that often in small print have an assumed X shift…X being 1.5 often.


    Andrew Parr

    @cseider is right and also I think you have made it more complicated by mixing defective opportunites per unit with defective units. How many defects does it take you to have a defective unit? Is it one or is it 11 or is it something in between?

    If it is only one then in reality there may be different ways of achieving that one but if it kills the item as a defective one then realistically I’d suggest there’s only one opportunity after that you stop counting. On that basis I think your at around 2.9 Sigma rather than 3.9 sigma.

    Just my opinion but opportunities has always misled me in the past so I hope I’m right now!



    Thank you Mr.Andrew… i got the point :)

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