As a quality management expert with a focus on statistical process control, I can explain the concept of defect rate within the Six Sigma framework.

Six Sigma is a set of techniques and tools for process improvement. The central aim is to minimize process variability and improve quality by identifying and eliminating causes of errors or defects. The term "Six Sigma" refers to the goal of the project: to find and eliminate as many as six standard deviations from the mean of a process.

The defect rate for a Six Sigma process is typically measured in terms of DPU (Defects Per Unit) or DPMO (Defects Per Million Opportunities). The goal of Six Sigma is to achieve a defect rate of 3.4 DPMO, which means there would be only 3.4 defects in every million opportunities.

To put this into perspective, a Six Sigma process is about 99.99966% free from defects. This is a very high standard of quality and represents a significant reduction in the variability of a process.

read more >>

In the Six Sigma context, PPM is also referred to as the PPM defect rate. Similarly, 3.4 PPM is often stated as 3.4 defects per million parts. In both examples, however, when we say defects, we are really referring to defectives.read more >>