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TOPIC: Control chart question

Control chart question 2 years 10 months ago #9579

  • Lawrence Li
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Hi all, this question from Oliver Lehmann

I wonder why the answer is A? Thanks
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Last edit: by Cornelius Fichtner.

Control chart question 2 years 10 months ago #9608

  • Steven McClaugherty
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This is a good question and am curious about the answer as well, and explanation of why something should be adjusted or improved. I tried to research to see if I could find some additional interpretation (other than Rule of 7 or exceeding a control limit).

Based upon the answer being A, so if a chart that is high precision and low accuracy needs "adjusted", then does that make a low precision and high accuracy needs "improved"? If we say adjusted or improved with the process, what would be a proposed action/change (as an example?)

I am trying to think of how to interpret this. Would it mean?

Low Precision and Low Accuracy = is the visual here there is a great scatter on both sides of the mean up to/near control limits?
Low Precision and High Accuracy = needs improved?
High Precision and Low Accuracy = needs adjusted (according to the answer)
High Precision and High Accuracy = near perfect world (on or at the mean) no change based on deviation assigned.
Is there any meaning when you have more data points on one side of the mean than the other (aside from violating Rule of 7)?

Are there any other example charts that show visually what the control process would look like based on the other 3? Did anyone have Control Chart questions on their PMP exam? If so, do you recall what you had to identify with it? I don't want to get too far down in the weeds.

Thanks.

Control chart question 2 years 10 months ago #9622

  • Lawrence Li
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I just searched for other comments on the web (very few source) saying that
high precision with low accuracy then adjust
low precision with low accuracy then improve

what I can do now is to braindump this

Control chart question 2 months 3 weeks ago #18496

  • Ashvini K. Chhabra
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My query is also same. I couldn't find the info under what situation adjustment or improvement is needed. PMBOK6 doesn't explain it. Incase any resource is available , please share the name or weblink.

Control chart question 2 months 3 weeks ago #18527

  • KADIR VEDACHALAM
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Hello,
Would be interested to get more feedback on my input.
1. High precision because most of the points are close to each other.
2. Low accuracy because most are away from/above the mean (x bar) specified.
3. I think X bar shown is a clue. X bar means statistical mean (sum of value of all points /no of points).
4. It's stated that the machine is high accuracy high precision, so reliable measurement.
5. So the process is good, but representation in the control chart may need adjustment (adjustment of limits, and subsequently, the mean).
6. The actual mean (x bar) may be slightly higher.
7. Adjustment may mean adjustment of the chart and improvement may mean improvement of the process.

Will be great to understand a Quality Guru's perspective.
Thanks

Control chart question 2 months 2 weeks ago #18565

  • Rrr Rrr
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Here is a brief explanation of the difference between both terms : (a detailed explanation is available in PM Study Circle's article " Precision Versus Accuracy")

Accuracy: Accuracy is defined as how the measured values are close to the target value.
Precision is when the values of repeated measurements are clustered and have less scatter.

in the question above, values are clustered around the USL (hence precise) but are not all close to the target (hence not accurate)
Last edit: by Rrr Rrr.
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