You can use the Xbar-R or Xbar-S chart for processes with continuous data. This chart is an industry standard for monitoring and controlling process outputs over time. While you usually use the XBar-R and Xbar-S charts with subgroups that are the same size, you can also use them with different size subgroups to accommodate botched measurements or missing data.
|When to Use||Purpose|
|Pre-project||Assist in project selection by identifying outputs that exhibit high common-cause variation, frequent special causes, unstable variation, or other symptoms pointing to the need for improvement.|
|Start of project||Verify process stability when performing a baseline capability analysis.|
|Mid-project||Investigate effects of input variables on the process output over time.|
|Mid-project||Verify process stability when performing confirmation runs after implementing improvements.|
|End of project||Verify process stability after implementing controls to obtain a final assessment of process capability.|
|End of project||Graphically compare the pre-project process dynamic behavior to the post-improvement dynamic behavior.|
|Post-project||Control inputs to the improved process after project is complete.|
|Post-project||Monitor output of the improved process after project is complete.|
Continuous Y, data collected in rational subgroups.