Use Capability Analysis (Normal Distribution) to assess the capability of an in-control process when the data are from the normal distribution or when the data are Box-Cox transformed. A capable process is able to produce products or services that meet specifications.

The process must be in control before you assess capability. If the process is not in control, then the capability estimates will be incorrect.

Normal capability analysis consists of a capability histogram and a table of process capability statistics.

An engine manufacturer uses a forging process to produce piston rings. The forging process is in control, and now the quality engineers want to assess the process capability. Twenty-five samples of five measurements of the inner piston ring diameter were collected. The specification limits for piston ring diameter are 74.0 + 0.05.

Data source: Douglas C. Montgomery (1996). Introduction to Statistical Quality Control. John Wiley & Sons, New York.

Data: Piston.MTW (available in the Sample Data folder).