[R] boxplot notches

[Thomas Lumley]

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.


	-thomas