Process capability Stable process

Six Sigma – iSixSigma Forums Old Forums General Process capability Stable process

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    Hi Friends,
    The basic statistical principle is “Calculate process capability only if the process is Stable”.But in many cases i have seen some companies just take 50 samples & calculate process capability using Histogram directly.Some customers also insist for this.My question is – Is there any method other than Control Charts  to Know whether the process is stable or not & whether computing process capability before verification of  stability is acceptable? if yes under what conditions ?


    Rohit Madhavan

    Let me answer the second part of your questions regarding stability and capability. It would not be correct to calculate the process capability unless the process is stable and predictable. Under unstable conditions the capability would not be the true or correct one.



    When you calculate the metric with all the datapoints together, without a control chart, and using as estimation of sigma the sample’s standard deviation, it is customary to call it “process performacne” instead of “process capability”.
    You can search this forum for hours and hours of discussion about this subject.

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