How to Link Yield and Defect Rate for Six Sigma - dummies

How to Link Yield and Defect Rate for Six Sigma

By Craig Gygi, Bruce Williams, Neil DeCarlo, Stephen R. Covey

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.