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Re: st: Interpretation of Two-sample t test with equal variances?


From   "JVerkuilen (Gmail)" <jvverkuilen@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Interpretation of Two-sample t test with equal variances?
Date   Wed, 20 Mar 2013 20:45:10 -0400

On Wed, Mar 20, 2013 at 7:50 PM, David Hoaglin <dchoaglin@gmail.com> wrote:
> Jay,
>
> If the way people teach boxplots is the (main) source of the
> difficulty, I would not be inclined to blame the boxplot!

True.

> I'm not sure what you mean by "the box ends up being too big" if the
> data are light-tailed.  I would expect the "whiskers" to be unusually
> short.

That was my way of saying that the whiskers were too short.



> A boxplot can do only so much.  The display was not designed to reveal
> bimodal or multimodal data.  A dotplot would usually show that
> structure easily.

Graphics, by their very nature, make assumptions about the data
because they provide data reduction. The boxplot provides a lot of
data reduction as it takes a variable from N observations down to 5
plus a few. So the boxplot's key assumption is that the data are
unimodal.

I guess I agree with Nick that they've been oversold, but as I say I use them.
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