here is some help info from minitab about trimmed means ...
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Trimmed mean
The trimmed mean (TrMean) is like the mean, but it excludes the most
extreme values in the data set. The highest and lowest 5% of the values
(rounded to the nearest integer) are dropped, and the mean is calculated
for the remaining values.
For the precipitation data, 5% of 11 observations is 0.55, which rounds to
1. Thus, the highest value and the lowest value are dropped, and the mean
is calculated for the remaining data:
1 2 2 3 3 3 3 4 4 5 10
This yields a value of 3.222. Like the median, the trimmed mean is less
sensitive to extreme values than the mean. For example, the trimmed mean of
this data set would be 3.222 even if there were 30 days with precipitation
in April instead of 10.
© All Rights Reserved. 2000 Minitab, Inc.
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keep in mind that if the data set is symmetrical ... then, trimming really
accomplishes nothing ... when it comes to the mean ... even if there are
extreme values ...
in a seriously + skewed distribution ... then trimming (for the mean) will
back up the mean more to the LEFT ... compared to non trimming ... and just
the opposite for a seriously - skewed distribution ...
as i said earlier, trimming will necessarily DECREASE the variability ...
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