The Impact of Measurement Error on Control Charts

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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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Measurement Systems Analysis/Gage R&R

Comments (4)

  • DaleWFebruary 1, 2018 Reply

    Doesn't it seem odd that Dr. Wheeler defines a determination coefficient (r²) but names it as a correlation coefficient (r) ?Seriously, wouldn't "process determination coefficient" make a lot more sense than "Intraclass Correlation Coefficient" ?

    • billFebruary 1, 2018 Reply

      Yes.  I had not heard the term "Intraclass Correlation Coefficient" before reading his book.  Might go along with his calling control imits "process behavior limits".  

  • AnonymousNovember 16, 2021 Reply

    some though from a beginner who reads AIAG MSA manual recently, shouldn't it also considered the impac the measurement error has on process capability? if the measurement erro is way too large like the 50% example for instance, it would potentially make wrong decison (type 1 error?) agianst process capabiltiy or which is explained in appedix B of the MSA manual, that could be reaosn AIAG recommend the minimum measurement error should be 30% as the differnce between actual & obseved process capability is still acceptable. in other words, if the observed process capabiliy is 1.33 based on measurement error of 50%, the actual process capabilty could be higher than 1.33, so it will be no need to make any improvement on both measurement system of production process

    • billNovember 18, 2021 Reply

      The value of sigma used in the Cpk calculations of course contains measurement variation as well as process variation.  If the measurement system variation is very high, you can work on reducing that to improve the process capability.  But the actual process capability contains the variation due to the measurement system and the product – both.  You can't separate them.  Reducing variation in the product or the measurement system will both improve the process capability.

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