Six Sigma
Definition
A quality methodology targeting 3.4 defects per million opportunities (DPMO). The name refers to having 6 standard deviations between the process mean and specification limits. Cpk = 2.0 represents Six Sigma capability.
Practical Note
True Six Sigma (±6σ) allows for 1.5σ shift over time, resulting in 3.4 DPMO. Without shift allowance, ±6σ would be 0.002 DPMO. Six Sigma projects use DMAIC methodology.