[BioC] qqplot: theoretical Quantiles

[Naomi Altman]

Limma has a qqt plot for checking against a t-distribution.

Some packages do have the quantiles for F, etc, but I cannot see one in R.

However, it is readily done in any of several ways:

1) Use the quantiles, just as with the Normal
2) Generate several samples of the required size; 
sort each; take the means of the smallest, 2nd smallest, etc

--Naomi

At 06:12 AM 10/22/2006, shahrgol at web.de wrote:

>Hi Noami,
>Thanks for your explanation.
>I understood qqnorm function in such a way:
>The theoretical quantiles is computed by standard normal distribution.
>
>x = µ + zσ (and/ or: z = x- mean/SD)
>
>Is also the other theoretical distributions 
>(e.g. F-Distribution or t-Distribution) in R used?
>
>Thanks,
>Mohammad
>
> > -----Ursprüngliche Nachricht-----
> > Von: Naomi Altman <naomi at stat.psu.edu>
> > Gesendet: 22.10.06 04:24:24
> > An: Mohammad Esad-Djou <shahrgol at web.de>
> > Betreff: Re: [BioC] qqplot: theoretical Quantiles
>
>
> > In theory, the idea is that if
> >
> > y1 ... yn are i.i.d. F, we sort them into
> >
> > y(1)<y(2)< ..<y(n)  and plot these against the expected value of the
> > smallest, 2nd smallest, etc from a sample of size n generated from F.
> >
> > Taking such an expectation is difficult, so usually an approximation
> > is given based on the quantiles of the proposed distribution:
> >
> > F(1/(n+1)), F(2/(n+1) ) ... F(n/(n+1))
> >
> > I have not looked at the R documentation to see the exact
> > approximation used, but you can probably find it if you dig a bit.
> >
> > --Naomi
> >
> >
> >
> > At 01:10 PM 10/21/2006, you wrote:
> > >Hello,
> > >
> > >I use qqplot and would like to know, how 
> theoretical quantiles is computed.
> > >Is there source about it?
> > >
> > >Thanks,
> > >Mohammad Esad-Djou
> > >
> > >IZBI- Uni-Leipzig
> > >
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> >
> > Naomi S. Altman                                814-865-3791 (voice)
> > Associate Professor
> > Dept. of Statistics                              814-863-7114 (fax)
> > Penn State University                         814-865-1348 (Statistics)
> > University Park, PA 16802-2111
> >
>
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Naomi S. Altman                                814-865-3791 (voice)
Associate Professor
Dept. of Statistics                              814-863-7114 (fax)
Penn State University                         814-865-1348 (Statistics)
University Park, PA 16802-2111