Chapter 14

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^[] Bob Lawson and Ron Stewart, Measuring Six Sigma and Beyond: Continuous vs. Attribute Data (Schaumberg, IL: Motorola University Press, 1997), p. 16.

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^[] A warning for the technical types: PPM and DPMO aren't really synonymous, so be careful. Many people assume or intend PPM to signify defectives units—so 6σwould mean 3.4 "bad" units for every million produced. In our electronic components example, however, we noted that each item has roughly 4000 opportunities. Using the DPMO calculation, you would therefore reach 6σperformance with 3.4 defects for every 250 units (250 units × 4, 000 = 1, 000, 000 opportunities). If defects were one to a unit, your Yield would be 98.64 percent and your total defectives for every million electronic components would be 13, 600. Pretty good for a complex product, but a lot more than 3.4!

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^[] For our discussion and examples here, we'll assume only one defect opportunity in our Sigma calculations. Determining opportunities gets trickier for internal process measures.

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^[] Another method to calculate the internal yield is called "Rolled Throughput Yield." YRTP is generated by multiplying the yields from each of the substeps. In our example this would be: .98 ×.99 ×.97 =.94

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^[] Cost of Poor Quality (which we introduced in Chapter 6) also is known as "Price of Non-Conformance" or "PONC." The related measure, "Cost of Quality," includes the costs of both rework and defects (i.e., poor quality), as well as the costs of solutions, prevention, and appraisal/prevention (i.e., achieving good quality).