Understanding the Process Capability Indicies

The process capability indices are a standard, albeit misunderstood, method by which engineers quantify and grade process performance. Unfortunately, the terms that compose the indices and how the indices are calculated are not widely understood. The Broken Quality Initiative is on a mission to change that with Understanding the Process Capability Indices.

After reading this document and completing its exercises, readers will be able to:

• Calculate the terms that compose the process capability indices
• Understand the difference between Sigma(X) and the standard deviation (s)
• Calculate the process capability indices (Cp, Cpk, Pp, and Ppk)
• Explain the differences between the capability ratios (Cp and Cpk) and the performance ratios (Pp and Ppk)
• Interpret the process capability indices as standalone values and through comparison with each other
• Understand why the indices should ALWAYS be presented in the context of a process behavior chart and capability histogram

If you want to eliminate the confusion that plagues these indices, and impress your peers along the way, look no further than Understanding the Process Capability Indices.