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Ppk index
A Process Performance Index . A measure
of properties of a given set of output from a process (ex: a batch or lot) based on the observed variation in a sample.
Ppk= MIN[Ppu , Ppl]
where
Ppu = zUSL / 3
Ppl = - zLSL / 3
For Normal Distributions, the z-value for the USL and LSL are calculated as:
zUSL=(USL-GrandAverage)/SampleSigma
zLSL=(GrandAverage-LSL)/SampleSigma
For Non-Normal Distributions, the z-value for the USL and LSL are calculated by estimating the percent of the fitted distribution
beyond each specification limit, then converting those percentages to z-values for the Normal distribution.
See also:
Process
Capability Charts
Pp
Pr
Ppm
Process
Performance
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