Assignable causes of variation may be found and eliminated.
—WALTER A. SHEWHART
In the last chapter, we learned how to design new processes, analyze existing processes, implement reengineered processes, and manage throughput. But once you have a good process in place, how do you keep it running smoothly? How will you know if it’s “under control”?
In the arena of process quality, control has a very specific meaning and is defined in statistical terms. Don’t panic if you’re mathphobic. Conceptually, a process is under control if the quality measures taken are not improbable. In other words, your process is out of control if you take samples and get results that would be highly unlikely to occur if it were in control.