Six Sigma For Dummies
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Yield and defect rate aren’t completely independent of each other for Six Sigma. When you have an overall process with a relatively low defect rate — say, a process that produces units with a DPU less than 0.10 (or 10 percent) — you can mathematically link the process defect rate to the overall process yield with the following equation:


where e in the equation is a mathematical constant equal to 2.718.

You can find a function or key for raising e to a power on any scientific calculator or computer spreadsheet program. (Look for the ex key on your calculator.)

The actual value of the constant e is 2.71828182845905. . . . The decimal digits of e go on forever, never repeating. But you don’t need to know the details of this curious constant called e to excel at Six Sigma.

The power of this mathematical link between yield and defects is that if you can only measure or have only measurements of the defect rate of a process, you can still calculate its rolled throughput yield. A little bit of algebraic contortion provides an equation to calculate DPU based only on the rolled throughput yield of a process:

DPU = –ln(RTY)

where ln is the natural logarithm.

Every scientific calculator has an ln button.

About This Article

This article is from the book:

About the book authors:

Craig Gygi is Executive VP of Operations at MasterControl, a leading company providing software and services for best practices in automating and connecting every stage of quality/regulatory compliance, through the entire product life cycle. He is an operations executive and internationally recognized Lean Six Sigma thought leader and practitioner. Bruce Williams is Vice President of Pegasystems, the world leader in business process management. He is a leading speaker and presenter on business and technology trends, and is co-author of Six Sigma Workbook for Dummies, Process Intelligence for Dummies, BPM Basics for Dummies and The Intelligent Guide to Enterprise BPM. Neil DeCarlo was President of DeCarlo Communications.

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