Question

Explain the rationale of Six Sigma’s target of 3.4 NPMO?

Answer 1

NPMO is nothing but non-conformities per million oppurtunities and it can be called synonym to PPM i.e. part per million. Now when we say process is 2 sigma then we have 68% of the data within +/- 1 sigma of the mean, similarly when we talk about 6 sigma we have 99.7% of the data within +/- 3 sigma of the mean. which means only 0.0034% of the parts being produced will be defective or non-confirming.

Hence comes the definition of 3.4 NPMO that maximum of 3.4 defects or non-confirmities per million oppurtunities.