QQ plot x-axis values

[Paul Matthias Diderichsen <paulmatthias.diderichsen@abbott.com>]

Dear S-plus users.
I learned more or less all I know about
Q-Q plots by reading http://en.wikipedia.org/wiki/Qq_plot and related ressources
on the web. I think that I now understand more or less how these beasts
work.

Of course, there's still one issue:
There seems to be a discrepancy between what wikipedia says and what S-plus
does.

> a<-data.frame(NORM=rnorm(3))
# a$NORM could be any 3 values since
I'm only interested in x below...
> qqmath(~NORM,data="">
[1] -0.9674216  0.0000000  0.9674216
> qnorm(c(1/6,3/6,5/6))
[1] -0.9674216  0.0000000  0.9674216

versus: "k/(n + 1)-quantiles of
the comparison distributon (e.g. the normal distribution) on the horizontal
axis (for k = 1, ..., n)"

In the example above, I create a qqplot
with three points. As I understand wikipedia, these should be (on the x-axis)
at the 1/4, 2/4, and 3/4 quantiles of the normal distribution. However,
instead they are at the 1/6, 3/6, and 5/6 quantiles.

I'd appreciate it a lot, if anybody
can explain to me what is "right". (Of course: Gurus - feel free
to correct/add to the wikipedia entry in case it's not accurate!)

Kind regards and TIA - PMD.
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