[R] boxplot notches

[kjetil@entelnet.bo]

On 1 Mar 2004 at 9:54, Thomas Lumley wrote:

> On Mon, 1 Mar 2004, Christoph Scherber wrote:
> 
> > Dear list members,
> >
> > Can anyone tell me how the notches in boxplot(Y~X,notch=T)  are
> > calculated? What do these notches represent exactly? I´d suppose
> > they are Conficence Intervals for the median, but I´ve also been
> > told they might show Least Significant Difference (LSD) equivalents.
> 
> The help page says that " If the notches of two plots do not overlap
> then the medians are significantly different at the 5 percent level."
> 
> The only thing wrong with this is that it isn't true.  The code says
> that the notches are +/- 1.58 IQR/sqrt(n), so I think the claimed
> confidence level holds only for normal distribuitons with small
> amounts of contamination.
> 

Couldn't this be replaced with confidence limits based on order 
statistics, which are nonparametrically correct, although they take 
some more to compute.

Kjetil Halvorsen

> 
>  -thomas
> 
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