Capability Analysis and Negative Sigma

Six Sigma – iSixSigma Forums Old Forums General Capability Analysis and Negative Sigma

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    Hello Gurus,
    I have 2 questions that I hope someone can help answer…
    1) Can you have negative sigma level for a process? If so, can someone explain the intreptation – I have seen it in Minitab output – but cannot explain what a -0.23 sigma level means.
    2) I have binomial data and run capbility analysis – I can easily explain using analogies like trying to kick a football thru goal post and width of the goal post, etc… for continuous data – the graph is pretty – it makes sense – has upper and lower specs, etc… However with Binomial I am confused on how to explain to layman the meaning of the binomial output from Miniab.
    Hope this all makes sense.



    Srini:1) Negative sigma only means you have a DPMO greater than 500,000. This is usually because the mean value of your CTQ is outside either the USL and LSL.2) Explain that having a proposal hit rate of less than the USL means you are probably overpricing them and customers are going with your competition. A proposal hit rate greater than the USL probably means you are underpricing them and customers jump to accept them and you will be losing margin.Cheers, BTDT



    A negative cpk in terms of goal posts means that you missed the extra point (provided that you had previously scored a touchdown) or that you missed the field goal (you’ll have to kick from a shorter range).

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