could anyone advise whether there is an advantage to establish baseline metrics utilizing PPM vs DPMO. All of the 6 Sigma training I’ve read consistently refers to DPMO. For all intents and purposes, isn’t it 6 of-one and a half-dozen of the other?? thank you – jules Ianniello
PPM defects will not allow you to identify your problems nor tell if you are improving or getting worse in any particular area of the plant… especially when you are trying to see the efficiency of the company department by department, or as a whole. Yes, you can tell if your TV production had 30 PPM defective tuners. But next week the tuners may be OK and the horizontal controls may have 30 PPM. 30 is 30. Your data for the company as a whole may look like nothing changed. DPMO is the square root of the sum of all the different defect types (each) squared. Thus, any change in the defect types or quantities anywhere in the factory will show up in the reported numbers. All are standardized to a sigma level. Therefore, 2 defects with only one type of oportunity for failure in on department can be compared on the same performance scale as the 30 types of defects that can have interdependant failure modes resulting in combinations and permutations that could have hundreds, thousands, or millions of DPMO in a single computer chip design. Thus, it’s like sending up flares throughout the factory every time a quality level shifts by quantity or by location.
Look let’s try to keep this stuff simple. If you are
interested in comparing or benchmarking the quality
across many different products or services in or outside your company than you should use the dpmo metric. If you are tracking the quality performance of
one product or service system over time ppm or dpm is
fine. Essentially, the use of opportunities provides a way of standardizing the complexity for the purposes of making comparisions.
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