A common mantra in Six Sigma is to “make decisions based on data”. This is a flawed strategy that probably comes from Six Sigma’s dependence on statistical experts instead of business experts. A Six Sigma Black Belt or Master Black Belt is only as good as their business leadership skills. This is why a form test for Six Sigma certification will not work. A form test cannot measure leadership skills or business acumen. You need the full package to be effective. This is why so many Six Sigma initiatives fail. There is too much emphasis on math skills and not enough on business acumen and leadership.
Anytime we draw conclusions from statistical inference, other process evidence must support the conclusion. Statistical evidence is only half of the voice of the process. The big picture includes a thorough look at the practical significance of the statistical result.
One area that gives many process improvement teams difficulty is the selection of an acceptance level that is consistent with the reality surrounding the process. There are no hard and fast rules that can help to ensure the selection of the best acceptance criteria. This requires the observation of the process, an evaluation of the business’ objectives, an understanding of the business’ economic realities, and most importantly, the CTQs of the business’ customer base. For example, the acceptance criteria for the safety of an airplane might be set at 0.2 instead of 0.5.