At Six Sigma, what does the level mean in terms of defects per million?

At Six Sigma, what does the level mean in terms of defects per million?

• A. 99.999% of manufactured items are within the specification (or only 3.4 defects per million)
• B. 95% within specification (50,000 defects per million)
• C. 99% within specification (10,000 defects per million)
• D. 100% zero defects

Answer: (A)

Six Sigma measures quality by defects per million opportunities (DPMO). At this level, the aim is about 3.4 defects per million opportunities, which corresponds to roughly 99.99966% of items meeting the specification. The 3.4 DPMO result comes from accounting for a 1.5 sigma shift in long-term process performance, so the stated interpretation—only a handful of defects per million and almost all items within spec—is the essence of Six Sigma. Other descriptions with higher defect rates, like 95% or 99% within specification, imply far more defects per million and don’t match the Six Sigma target. Zero defects is an ideal not typically achievable in practice, whereas Six Sigma targets a near-perfection level reflected by about 3.4 defects per million.

Six Sigma measures quality by defects per million opportunities (DPMO). At this level, the aim is about 3.4 defects per million opportunities, which corresponds to roughly 99.99966% of items meeting the specification. The 3.4 DPMO result comes from accounting for a 1.5 sigma shift in long-term process performance, so the stated interpretation—only a handful of defects per million and almost all items within spec—is the essence of Six Sigma.

Other descriptions with higher defect rates, like 95% or 99% within specification, imply far more defects per million and don’t match the Six Sigma target. Zero defects is an ideal not typically achievable in practice, whereas Six Sigma targets a near-perfection level reflected by about 3.4 defects per million.