TOPIC: Accuracy and Precision

Hi,

I would appreciate if you could explain this question (control chart attached):

You were able to obtain measuring equipment with very high accuracy and precision. You used it to make a sequence of measurements directly at a production process output and depicted the results on the following control chart.
(control chart attached)
Which statement is the best conclusion from these results?
(A)The process has high precision but low accuracy. It should be adjusted.
( B ) The process has high precision but low accuracy. It should be improved.
(C) The process has high accuracy but low precision. It should be adjusted.
(D) The process has high accuracy but low precision. It should be improved.

Correct answer is (A). In my opinion, the process has low precision and low accuracy, according the definiton of both (attached representation), since lots or measures are far from the mean and close to the upper specification limit (low accuracy) and the measures don't usually have the same values (low precision).

Hope you can help me understand. Thanks!
Julia

Julia,

When posting sample questions in our forum, please always include a reference to where it is from.

Therefore, please add a note where you have found this. Thank you.

Hi, I found this at Oliver F. Lehmann prep test (200 Prep Questions), Question 9.

Can someone explain this question result please?
Thank you very much!

Hi,
Here I see 2 key information
- You are inside the USL - LSL
- Base on the rule of 7, you don't have 7 consecutive points above or below
So it means it's high precision, the choice should be between A & B only
Next question is shall we improve or adjust?
as we are high precision and low accuracy : so you need to adjust
Conclusion : Option A,
You should not compare a target with a control chart, it's not the same logic here:
on a target you can't define which is the first, second.... dots... on a control chart you can. so it's the rule of seven that will tell you if you are precise or not.