Calculating DPMO

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    I was just wondering if someone knows a general calculation for DPMO on the basis of the capability values Cpk and Cp? I would like to construct a matrix with Cp on the y-axis and Cpk on the x-axis. You should be able to look up any DPMO if you know what the capability values are.



    There is not necessarily any relationship between Cp and Cpk. Cp is the capability of the process to meet a given tolerance spread. (i.e. Cp=6sigma/total tolerance). Cpk takes into account how well centered the process is in relation to the tolerance limits. The Cpk is the minimum of the Cpkupper and Cpklower.
    You could have a Cp of 6.00 and at the same time have a Cpk of 0 or -0.10. It all depends on the spread of the distribution and the degree of centering.
    A matrix with Cp on one axis and Cpk on the other would not be appropriate. However, you could develop a matrix showing DPMO for long term yield/long term sigma/short term sigma. Most texts on Six Sigma I’ve seen contain this matrix to save you the time of creating your own.
    Good luck

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