Statistical Process Control (SPC)

PC
Alice, China
What is the difference between PPK & CPK?

What is the difference between PPK & CPK?"
Lo.Max, China
PPK is measured by unknowed process, cpk is measured by stable process

Cpk or Ppk??
Jacques-Alain TIAKO, Manager, France
Cpk - It's the capability index for a stable process (the process must be in a state of statistical control). The sigma calculation is based on within subgroup variation.
Ppk - It's the performance index (the actual process PERFORMANCE). The estimate of sigma is based on total variation. Ppk must be calculated if less than 100 samples or when the process is chronically unstable but meeting the specifications and in a predictable pattern.

What is the Difference Between PPK & CPK?
Ger de Waard, Management Consultant, Netherlands
In the Six Sigma quality methodology, process performance is reported to the organization as a sigma level. The higher the sigma level, the better the process is performing.
Another way to report process capability and process performance is through the statistical measurements of Cp, Cpk, Pp, and Ppk.
Definitions
• Cp = Process Capability. A simple and straightforward indicator of process capability.
• Cpk = Process Capability Index. Adjustment of Cp for the effect of non-centered distribution.
• Pp = Process Performance. A simple and straightforward indicator of process performance.
• Ppk = Process Performance Index. Adjustment of Pp for the effect of non-centered distribution.
Cp and Cpk are for computing the index with respect to the subgrouping of your data (different shifts, machines, operators, etc.), while Pp and Ppk are for the whole process (no subgrouping).