A bottling company wants to reduce the amount of overfilled bottles.On the basis of the data above, what is the most effective strategy to accomplish this task?
(A) Decrease the target fill volume only (B) Decrease the target fill variation only (C) First decrease the target fill volume, then decrease the target fill variation (D) First decrease the target fill variation, then decrease the target fill volume.
Common Causes vs Special Causes of Variance is the 5th post in our PMP Concepts Learning Series.
The best treatment is to look at all of the data available for the process and try to gain a better understanding of the system.
You could then make basic, impactful changes to your process that would improve the whole.
Experience had shown that, amongst the people in and around the process, there are enough ideas for improvements to make a significant impact, even on a sound process. This page was written by Steve Simon while working at Children's Mercy Hospital. You can also browse for pages similar to this one at Category: Control charts, Category: Definitions.
Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website.
If you were to treat special cause like common cause, you would be over-deploying resources to fight an problem that isn’t as likely to happen.
For example, if shipping was delayed due to a once-in-a-generation storm and you pivoted all of your attention to fixing the process for when that storm hit, you would de-prioritize other more likely, and more meaningful process improvements. Fun game illustrating variation. (within unit/sample), Cyclical (part to part) and Temporal (time to time) to pool variances)https://en.wikipedia.org/wiki/Common_cause_and_special_cause_(statistics)Tolerance – Additive law of variance (Use square root of sum of individual variances to find the total variance) This section requires you to be logged in to either a Pass Your Six Sigma Exam or a free account. Login to your account OR Enroll in Pass Your Six Sigma Exam OR Get a Free Account Questions, comments, issues, concerns? Question: Legal requirements specify that a bottled product must contain at least the volume printed on the label.
When a work process has only common causes of variation and no special causes, that process is "in control." This means that it is stable, consistent, and predictable.
It might be predictably good or predictably bad, or it might be a very regular mix of good and bad results. Just because a process is stable, or in statistical control, does not mean that its results are satisfactory.
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