During a recent quality training session, the class discussion centered on quality metrics and the frustration they can cause. With the plethora of metrics being used in many quality systems, people can become confused because of the subtle differences among the metrics. While this column cannot take the space to properly define the metrics, we can discuss the foundation for interpreting defect-based metrics in a meaningful way.
To use a defect-based metric such as Percent Defective (PD), Defects Per Unit (DPU), Defects Per Million Opportunities (DPMO), Parts Per Million (PPM), Rolled Throughput Yield (RTY), etc., effectively, it is important that the organization answer two simple questions. First, what is a defect? And second, how can a defect occur?