Metrics Across Multiple Sites
You collect quality data to gain a competitive advantage, to improve your products and foster customer delight, to improve your processes and save resources, and to avoid recalls and regulatory issues. But you may have limited resources, so it can be difficult to tell where to expend effort. You'll need to find your areas with the greatest opportunities, identifying sites that need the most attention and sites that are the most successful. Once you find those areas of opportunities, you'll need to determine your next steps, whether that's equipment maintenance, operator training, or new equipment.
You collect a considerable amount of data across multiple lines and even across multiple sites, and you want a metric that summarizes the data across all sites. You may be tempted to use a capability metric, like Cpk or Ppk, or Parts per Million (PPM). However, to roll-up these metrics, you must first normalize your data in a centralized repository, and even if you're able to do this, those metrics aren't very actionable.
Consider the following two sites:
Despite having identical Pp and Ppk metrics, Site 1 needs process improvements on all lines, while Site 2 just needs to retarget. In addition, metrics like Cpk, Ppk, and PPM are just not intuitive to most users. However, most users readily understand the concept of Yield.
To learn about yield-based grading, please see Yield-Based Grading.