# DPMO convert to Cpk

Six Sigma – iSixSigma Forums Old Forums General DPMO convert to Cpk

Viewing 6 posts - 1 through 6 (of 6 total)
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• #29050

Baker
Participant

Can you convert DPMO to Cpk?  For example, a DPMO of 2700 is equal to ??? in Cpk.  Is there an equation to calculate this?

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#73458

Kurt Fifield
Participant

I have never heard of anyone calculating DPMO into Cpk, I know you can get your Z scores and RTY from the DPMO, don’t know if I helped you?

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#73471

lin
Participant

Because Cpk is calculated using the distance of the mean to the closest specification, the other side of the distribution is ignored by the Cpk calculation – so there is no single DPMO associated with a given Cpk. Two different processes could have the same Cpk but different DPMO’s.  Additional complications arise if there are multiple defect opportunities associated with different output characteristics – Cpk only measures one characteristic.

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#73537

Misael Gonzalez
Participant

The Cpk index works just for continuous data (usually from a normal distribution) and measures the location of the mean related with specs. The DPMO index is for defects or defectives, which resultant distribution curve usually is a Poisson or a Binomial distribution. In the case of the DPMO you only can obtain the Process Capability as a percentage of defects (or defective) or Z Values.
But you can obtain the Quality Levels in terms of Sigma Quality level using the next formula
Sigma Level= 0.8406 + sqrt(29.37-2.221Ln(DPMO)) it works!! and you don’t have to check the tables of probability to find the Z scores related with a given level of DPMO.

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#73551

Tim Johnson
Member

Why do you want to convert DPMO to Cpk?

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#96719

Corbin Jewell
Participant

I’d like to be able to convert DPMO to CpK because GEAE often requires a CpK to be reported even when it is not practical (such as an attribute).

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