A Look Back at Variation

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Thanks so much for reading our publication. We hope you find it informative and useful. Happy charting and may the data always support your position.


Dr. Bill McNeese
BPI Consulting, LLC

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Comments (3)

  • Costa, RicardoDecember 30, 2016 Reply

    Does the interpretation of XmR range chart, like the other variable control (Shewart´s) charts is reliable only if data follow a Normal Distribution? How can we check it? 

    • billDecember 30, 2016 Reply

      It is not a requirement that data be normally distributed to use a control chart.   Points beyond the control limits work pretty well regardless of the type of distribution.  The zones tests may give some false signals if the distribution is very skewed, as discussed in the article on Control Chart and Non-Normal Data.  As far as determining if data are normally distributed, please see our June 2016 artice: <a href="/knowledge/basic-statistics/what-my-data-are-not-normal">What?  My Data are Not Normal?</a>

  • NickDecember 31, 2016 Reply

    I wish you A very Happy New Year!

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