Pp/Ppk are process performance indices used to compare actual process variation with specification limits. They are commonly used in manufacturing quality analysis to describe how a process has performed over a defined set of production data.
Pp evaluates the overall spread of the process relative to the tolerance range, assuming the process is centered. Ppk also accounts for how well the process is centered by comparing the process mean to the nearest specification limit. Because Ppk considers both variation and centering, it is typically the more conservative of the two indicators.
Pp and Ppk are often discussed with Cp/Cpk, but they are not the same. Pp/Ppk usually use overall, long-term variation from the collected data, while Cp/Cpk often use within-subgroup or short-term variation, depending on the method applied. The distinction matters when interpreting whether the data reflects current production behavior, historical performance, or controlled capability study conditions.
In regulated or quality-sensitive manufacturing, Pp/Ppk values may be used in process capability analysis, production monitoring, supplier quality review, or continuous improvement work. Measurement data should be traceable, tied to the applicable design and process state, and supported by a statistically meaningful sample. First Article Inspection data may contribute context, but it is not a process performance study by itself.