Re: Box & whisker plots with skewed distributions?

Hi Bruce,

The following (from the Wikipedia page on box-plots) expands a
bit on what Rich said.
I had seen that, actually, but thanks for your reply.

* Indicate outliers by open and closed dots. "Extreme" outliers, or
those which lie more than three times the IQR to the left and right from
the first and third quartiles respectively, are indicated by the
presence of an open dot. "Mild" outliers - that is, those observations
which lie more than 1.5 times the IQR from the first and third quartile
but are not also extreme outliers are indicated by the presence of a
closed dot.
What I don't like about this is that I don't think these
extreme values are outliers in my data set, at least not
in the sense of an outlier as a data point generated (primarily)
by some process other than the one I am trying to study.

In general, I am very uncomfortable with any such hard
and fast definitions of outliers. In my area, people often
exclude outliers from their data sets (e.g., before
computation of means, etc). These sorts of statistical
guidelines seem to evolve quickly into statistical
dogma, leading people to exclude a data point
at q3+3.001*IQR but include one at q3+2.999*IRQ.
It seems to me that would probably be a mistake.

.

Relevant Pages

  • Re: Box & whisker plots with skewed distributions?
    ... those which lie more than three times the IQR to the left and right from ... "Mild" outliers - that is, ... extreme values are outliers in my data set, ...
    (sci.stat.edu)
  • Re: Box & whisker plots with skewed distributions?
    ... those which lie more than three times the IQR to the left and right from ... "Mild" outliers - that is, ... of outliers, which can lead statisticians astray, ...
    (sci.stat.edu)
  • Re: Running "mean"
    ... data set that is pruned of outliers all the way down to the median? ... These means form a chain that goes to the median of the set. ... "significantly" from that of the nth step, ...
    (sci.math)
  • Re: Running "mean"
    ... data set that is pruned of outliers all the way down to the median? ... These means form a chain that goes to the median of the set. ... Maybe comparing ...
    (sci.math)
  • Running "mean"
    ... Is there any statistical concept of a set of means that is computed for a ... data set that is pruned of outliers all the way down to the median? ... These means form a chain that goes to the median of the set. ...
    (sci.math)