[BioC] qqplot: theoretical Quantiles

[shahrgol at web.de]

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
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