Analyzes the difference between an observed process standard deviation (or variance) and a specified value.
|When to Use||Purpose|
|Pre-project||Verify the variability of the process is significantly different from expectations, validating the need for an improvement project.|
|Mid-project||Test whether a significant change has occurred in the variability of the output when an input is controlled at a new setting or a previously uncontrolled setting is now controlled.|
|Mid-project||Verify changes from the pre-project standard, throughout the course of making improvements.|
|End of project||Verify the variability of the controlled improved process is different from the pre-project variability. Of course, this assumes that one of the goals of the project was to reduce the variability of the process.|
Continuous Y (output).