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  • #29847

    DT
    Participant

    I was recently working with minitab during level 2 analyst training (GB).  A participant asked what the descriptive statistic data set listed as TR Mean meant.  Its been too long since I had statistics to remember.  The value was 14.08 and the absolute mean was like 14.2.  Can someone help with sparking my memeory?

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    #77140

    James A.
    Participant

    It’s the trimmed mean – Minitab removes the smallest 5% and the largest 5% values and then averages what’s left.
    (Courtesy of the Minitab Search Help thingy)
    How this is supposed to help anyone, I’m not sure, though – I suppose it removes some of the ‘wilder’ values (Outlier data???) and returns only the mean for the central chunk of the data.
    James A

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    #77142

    Robert Butler
    Participant

      As James A. observed, the trimming function will remove X% of the lowest and highest values in a distribution.  The idea here is to minimize the effect of “outliers” on the estimate of the mean.  Like all statistical methods this should not be done blindly.  If you have a situation where your data is normal and in the course of your investigation there was a upset that generated a few extreme points that will impact your estimate of the mean then trimming may be of value.  If, on the other hand, your data is not normal-too heavy tails, distribution skewed to one side, etc. then trimming will encourage underestimation and, as the inquisition said-you will go wrong with great assurance.

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