[R] chi square table
Berwin A Turlach
berwin at maths.uwa.edu.au
Fri Nov 7 03:16:28 CET 2008
G'day Cruz,
On Fri, 7 Nov 2008 09:47:47 +0800
cruz <cruadam at gmail.com> wrote:
> Hi,
>
> How do we get the value of a chi square as we usually look up on the
> table on our text book?
>
> i.e. Chi-square(0.01, df=8), the text book table gives 20.090
>
> > dchisq(0.01, df=8)
> [1] 1.036471e-08
> > pchisq(0.01, df=8)
> [1] 2.593772e-11
> > qchisq(0.01, df=8)
> [1] 1.646497
> >
>
> nono of them give me 20.090
The value that your textbook denotes, presumably, with chi^2_0.01 (or
some similar notatation) is in fact the 0.99 quantile of the chi-square
distribution; which R readily calculates:
R> qchisq(0.99, df=8)
[1] 20.09024
<rant on>
That's the problem with introductory textbook whose author think they
do the students a favour by using notation as z_alpha, z_0.01,
z_(alpha/2) instead of z_(1-alpha), z_0.99, z_(1-alpha/2),
respectively. In my opinion this produces in the long run only
more confusion and does not help students at all. It just panders to
intellectual laziness of (some) students and shows a great deal of
confusion on the side of the authors.
I would search another textbook
<rand off>
Cheers,
Berwin
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Berwin A Turlach Tel.: +65 6516 4416 (secr)
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