z-mR Control Charts for Short Production Runs

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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 (7)

  • Stephen PuryearJuly 31, 2015 Reply

    Thanks so much for the fun and educational article.  It made me dive a little into where the control chart constants came from, originally.  Also, I know that it is not easy to generate new fake data that illustrates a point.  By inspection, it looked to me as if the new data gathered after the "set" was not independantly drawn or had a special cause that made it look that way.  For example, the 30 point set data had about 21 "sign changes' in 30 data points.  The post set new data had ony one in nine points in which successive points had a different sign.  As we dug into the special cause, would we not want to pay special attention to factors common to both products?  Both products One and Two combined to create the "seven points above average" disturbance in our Z chart.  I plant to move some of this data over to "PAST" and look at it there.  Have you ever used this free app?  Its fun and has a lot of graphical power.Thanks again for the extra effort and may all of your data be true,Stephen Puryear

  • billAugust 1, 2015 Reply

    Thanks for you comment.  Actually the data comes from the book "Short Run SPC" by Dr. Wheeler.  I failed to reference that as I should have.  I agree on your statement about something common to both products – but if they are run on the same process with different settings, it could be just process.  What app are you referring to? 

  • Tim IngoldSeptember 16, 2016 Reply

    Does the software have Z-bar with R (between) and R (within) ?   In other words can the software handle short runs with sample sizes greater than 2 and look at variability.  Ie. Z-bar R(within) and R(between)?

    • billSeptember 17, 2016 Reply

      Hi Tim,
      The software uses individual values to determine z values – not subgroups.  So, you have the z chart with those z values and then you have a moving range chart for the values between consecutive z values.  

  • Stephen PuryearSeptember 25, 2020 Reply

    Hi, BillThanks for the rapid response.  "PAST" was originally designed for paleontologists but has steadily grown until many other users would find it useful.  The technical writing that supports the statistical tools is just about the clearest that I have ever read on which approach works for which problem, why it works and what their limitations are.  It is quite compatable with Excel and is frequently updated primarily for Windows environments.  Check it out!

  • Eng Heng LimSeptember 15, 2021 Reply

    Hi,  there are 7 points (points 31 to 37) of the Moving Range Chart  below the average line. Would this be considered out of control?

    • billSeptember 16, 2021 Reply

      No, with a moving range chart you are reusing each point twice, so the run has to be longer, like 14 points.

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