Ppk index

A Process Performance Index is a measure of both process dispersion and its centering about the average.To calculate, use the Ppk formula below.

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where

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Normal Distributions:

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Non-Normal Distributions:

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where x-doublebar is the Grand Average and ÃÆ’x is Sample Sigma .

Znormal,p and Znormal,1-p are the z-values of the normal cumulative distribution curve at the p percentage point and the 1-p percentage points, respectively.

Learn more about the SPC principles and tools for process improvement in Statistical Process Control Demystified (2011, McGraw-Hill) by Paul Keller, in his online SPC Concepts short course (only $39), or his online SPC certification course ($350) or online Green Belt certification course ($499).