Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down on April 23, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


From   David Hoaglin <dchoaglin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Interpretation of Two-sample t test with equal variances?
Date   Wed, 20 Mar 2013 15:14:58 -0400

Thanks, Nick.

I was going to suggest a dotplot, but held off.  The sample sizes are
large enough that some jittering may be helpful.

Preferences for plots may vary, but a thorough analysis should include
graphical displays of the data.

David Hoaglin

On Wed, Mar 20, 2013 at 12:58 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> I wouldn't want to start with box plots here. For two groups, there is
> space for more detail than a box plot gives, except capriciously in so
> far as points are more than 1.5 IQR from the nearer quartile.
>
> I grew up, as it were, on box plots, including David's own writings 30
> or more years ago, but I think they are oversold in total.
>
> I have often seen -- even in otherwise good textbooks -- people
> talking about t-tests or ANOVA and then giving box plots -- and not
> even commenting on the mismatch, i.e. that the box plots are showing
> medians etc., not means etc.
>
> A more directly relevant graph would, I suggest, be a dotplot (sensu
> -dotplot-) or even -stripplot- (SSC). You can show means on such
> plots.
>
> Nick
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index