I've noticed that the calculated Cpk in DataPage does not match what is calculated in Minitab on the same data set. We don't use DataPage except to collect data, but I'd like to preview statistical analysis before sending the data. Is this common? Are there different methods of calculating Cpk?
Check the DP settings. OPTIONS SPC CALCULATIONS CAPABILITY THRESHOLDS
DP & Excel Cpk match when using 4 sigma, 1.33 for the value (I think these are DP defaults)
However, check to see WHICH Cap Calc Rules are used. Mark the "Use estimated std. dev for Cp Cpk, etc. Use Sample std. dev for Pp, Ppk, etc." I have a feeling the other option may be checked, which sets Pp, Ppk, etc. to sample std dev.
...MiniTab uses a calculated StdDev based on the actual values and subgroups sizes rather than a "pooled or estimated" StdDev...otherwise...it's what Matt said,,,
Check the DP settings. OPTIONS SPC CALCULATIONS CAPABILITY THRESHOLDS
DP & Excel Cpk match when using 4 sigma, 1.33 for the value (I think these are DP defaults)
However, check to see WHICH Cap Calc Rules are used. Mark the "Use estimated std. dev for Cp Cpk, etc. Use Sample std. dev for Pp, Ppk, etc." I have a feeling the other option may be checked, which sets Pp, Ppk, etc. to sample std dev.
...MiniTab uses a calculated StdDev based on the actual values and subgroups sizes rather than a "pooled or estimated" StdDev...otherwise...it's what Matt said,,,
