Quality Quiz from Professor Cleary
"No" is the correct answer!
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Marsha and her sidekick Maura are getting better with their spontaneous responses, but they should be advised to stall further until they fully understand each situation. Buying donuts is one step that might be taken, but this situation involves additional actions.
Indeed, the chart reflects ten R’s below R-bar -- a positive signal for the fact that variability in the process has declined.
The first thing is to see what would be happening in a process to cause a run below R-bar. As sited above there was a run of ten R's below R-bar.
The below visual might provide some insight as to what would cause a run below R-bar. Figure A shows a process that is stable in terms of the range values. Figure B shows the variability being reduced starting at 10:00 which should lead to the range values getting smaller, possibly being below R-bar.
If you get a run below R-bar then there are three things you should do:
1. Finding out what has caused the change in the process (improvement, in this case).
2. Making whatever caused the improvement permanent.
3. Only after being assured that step #2 has been successful, both the R-bar and the control limits should be recalculated.
It should be noted that in application, step #1 can be difficult to do. A paper company with whom I worked, for example, took 8 months to track down the cause of variability in a paper manufacturing process. When the team finally determined what was creating the improvement, they were indeed treated to donuts.
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