Capability analysis, with its formulas and the confusion around Ppk, Cpk, Cpm, and other indices, is often perceived as far too difficult, complex, and challenging to consider utilizing. Good reasons for undertaking the analysis are sometimes not considered, in the light of this perceived complexity.
In fact, good reasons for using capability analysis not only exist, but provide compelling argument for utilizing this statistical tool. And it’s really not that hard.
Capability analysis offers a way to compare a process to a customer’s requirements, coming up with a score that facilitates communication with the customer to indicate how well a process is able to meet these requirements. Since the language and terminology surrounding capability analysis are consistent and generally agreed upon, discussions can be effective, and can initiate continued progress with meeting and surpassing the customer’s requirements.
In capability analysis, these customer requirements are expressed as specifications, not to be confused with control limits. Some examples of customer requirements (specifications):