Have you experienced the following? Consider that after implementing an improvement the process capability has improved from 3.5 sigma to 4.2 sigma. Proudly you celebrate this very nice Six Sigma methodology success in your organisation. How many questions did you get after or during your presentation about how important this improvement really is? What does this mean for the participants in your improvement team(s) and your management or the process owner? And even more important, what are the true consequences for the internal or external customers of this process?
Especially at the beginning of a six sigma deployment not many people in the organisation can relate to the sigma capability metric. Yes, some might already know that a 6 Sigma process produces 3.4 defects per million opportunities and that a 2 sigma process is a bad performing process with important defect rates. But do people understand the true impact of the improvement from 3.5 sigma to 4.2 sigma (regardless whether it is long or short term capability).
In any organization that has traveled on their Six Sigma journey, there are a lot of people that have heard about the sigma metric and know what it is (from white, yellow or green belt training or because they have participated in an improvement team) but have no real feeling of the process performance reflected by it.
Here is how to solve that problem: I find it much easier to make myself understood describing process capability improvements by the DPMO metric. Take the same numbers as in the example above. Substitute the initial 3.5 sigma capability by 22,750 DPMO and the after improvement capability 4.2 sigma by 3,467 DPMO. Participants in improvement teams, management and process owners will immediately sense the magnitude of the improvement made, defects reduced from 2.3% to 0.3%.