Question Regarding Xbar and R Charts

Six Sigma – iSixSigma Forums General Forums Tools & Templates Question Regarding Xbar and R Charts

This topic contains 2 replies, has 3 voices, and was last updated by  Mike Carnell 1 month, 4 weeks ago.

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    I came across this newsletter about X-bar and R charts. In the paragraph preceding the control chart example, the author says the following: In the bowling example, this means that you can predict what the average of your three games on any given night will be. Your average will be between 140 and 181 with a long term average of about 161. You can also predict what your range in bowling scores will be on any given night. The range can be anywhere from 0 to 52 with an average range of about 20.

    When I look at the charts, though, I don’t understand how the author came to the conclusion he did. From what I see, the average will be between 158 and 209 (not 140 and 181), with a long-term average of 181 (not 161). Likewise, the range would be anywhere from 0 to 61 with an average range of 25.

    Can anyone please explain this to me? An error, perhaps?



    Hi @chebetz,

    Your readings are correct. Probably the author altered the numbers but didn’t reflect that on the graphs. Happens to all of us once in a blue moon.





    Mike Carnell

    @chebetz I apologize for not getting back to you sooner. I had some IT issues and some other stuff that came up. I am seeing the same thing you are seeing

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