The Problem of In Control but Out of Specifications

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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)

  • Sergey Grigoryev, DEMING.PROFebruary 28, 2020 Reply

    Thanks,Great article! The second case is exactly what all lathe operators do without understanding the nature of variability. How can they know that? First of all, business management should know about this “problem”, which can be a huge opportunity.With respect, Sergey Grigoriev

  • Raphy BarMarch 1, 2020 Reply

    I would like to suggest to build on this example and ask you how would you proceed and what would you consider doing when a given result is out-of specification and you wish to confirm that it is either a real OOS or just a measurement outlier.This is a situation common in a pharmaceutical manufacturing process where an OOS result of a tested batch is obtained upon testing a pharmaceutical product and one carries out an investigation to validate or invalidate a given OOS. Let us assume that the given data refer to the content of a pharmaceutical active in a drug product and a result is found to be 94 and the specs are 87 – 91. The process is supposed to be stable and not with so many OOS as in the given example. What would you do? Re-test? How many times? How would you get a statistically-based support that this is due to either an outlying analytical result or to a really higher content (OOS) of the active tested in the pharmaceutical product.

    • billMarch 2, 2020 Reply

      You want to be sure that the test result is valid.  You do that by running a standard or control on a regular basis in the test method.  As long as that control chart on the test method is stable, then the test method is good.  Of course, it is possible that there was an issue on the one test that produced the 94.  But if the test method is in control with respect toe standard or control, i would assume it is really due to the higher content.  

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