Check assumptions

Before performing a process capability analysis for normally distributed data you should:

·    Make sure the process is in control. An out-of-control process results in an incorrect estimate of process capability. Use Minitab's control charts to determine whether your process is in control.

·    Make sure the data are normally distributed by using Minitab's probability plot. If the measurements are not normal, you can try to transform the data to normality using the Box-Cox transformation or Johnson transformation.