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Re: Quartiles

To: "'Dr. M.Sawada'" <msawada@uottawa.ca>, "'Prof Brian Ripley'" <ripley@stats.ox.ac.uk>, "'Heeringa W.J.'" <heeringa@let.rug.nl>
Subject: Re: Quartiles
From: "Monder, Harvey" <Harvey.Monder@pharma.com>
Date: Fri, 7 Dec 2001 13:15:49 -0500
Cc: s-news@lists.biostat.wustl.edu
And in SAS, Proc Univariate provides 5 algorithms (pctldef), the fourth
producing the same results as SPSS, but none of them producing the results
in Splus.
(As to the rightness or wrongness of SAS, I will leave that to your
discretion)

        Dr. H. Monder

-----Original Message-----
From: Dr. M.Sawada [mailto:msawada@uottawa.ca]
Sent: Friday, December 07, 2001 11:54 AM
To: 'Prof Brian Ripley'; 'Heeringa W.J.'
Cc: s-news@lists.biostat.wustl.edu
Subject: Re: [S] Quartiles



Incidentally, MS Excel uses the same quantile algorithm as S+ - and Bill
Gates is never wrong.

Dr. M.Sawada
Assistant Professor, GIS
University of Ottawa
Dept. Geography
P.O. Box 450 Stn. A
Ottawa, ON K1N 6N9
Tel: 613-562-5800 x1040
Fax: 613-562-5145
Eml: msawada@uottawa.ca 
 

-----Original Message-----
From: s-news-owner@lists.biostat.wustl.edu
[mailto:s-news-owner@lists.biostat.wustl.edu] On Behalf Of Prof Brian
Ripley
Sent: Friday, December 07, 2001 11:32 AM
To: Heeringa W.J.
Cc: s-news@lists.biostat.wustl.edu
Subject: Re: [S] Quartiles


On Fri, 7 Dec 2001, Heeringa W.J. wrote:

> Dear S-PLUS users,
>
> Assume I have the following range:
> 1 2 3 4 5 6
>
> Next I calculated the 1st Quartile, the median and the 3rd Quartile in

> both, S-PLUS and SPSS:
>
> 1st Quartile : S-PLUS: 2.25 and SPSS: 1.75
> median       : S-PLUS:  3.5 and SPSS: 3.5
> 3rd Quartile: S-PLUS: 4.75 and SPSS: 5.25
>
> Or for this range:
> 1 2 3 4 5 6 7 8
>
> the results are:
>
> 1st Quartile : S-PLUS: 2.75 and SPSS: 2.25
> median       : S-PLUS:  4.5 and SPSS: 4.5
> 3rd Quartile: S-PLUS: 6.25 and SPSS: 6.75
>
> So S-PLUS and SPSS give different results. Which results are correct? 
> And how can these results be explained?

Why don't you send a bug report to SPSS if they don't explain their
results?  If it's not in the on-line help it is a bug, but for S-PLUS it
*is* there.

There are several slightly different definitions of quantiles (and hence
quartiles), but ?quantile in S-PLUS tells you what it uses.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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