Overview for Between/Within Capability Sixpack

Use Between/Within Capability Sixpack to assess the assumptions for between/within capability analysis and to evaluate only the primary indices of process capability when your process produces large variation between subgroups. Using this analysis, you can do the following:

• Determine whether the process is stable and in control
• Determine whether the data follow a normal distribution
• Estimate overall capability (Pp, Ppk) and potential capability (Cp, Cpk)

To perform the analysis, you must specify a lower or upper specification limit (or both) to define your process requirements. The analysis evaluates the spread of the process data in relation to the specification limits. When a process is capable, the process spread is smaller than the specification spread. The analysis can also indicate whether your process is centered and on target. In addition, the analysis estimates the proportion of product that does not meet specifications.

For example, an engineer wants to assess the process capability of a paper coating process considering both within-subgroup variation and between-subgroup variation. The within-subgroup variation is the variation of coating thickness within one roll. The between-subgroup variation is the variation between rolls that may occur during machine resets. The engineer performs between/within capability sixpack to quickly evaluate the main capability indices and assess the assumptions for the analysis.