Quartiles in S-plus

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2 total messages Started by Toufik Zoubeidi Tue, 17 Nov 1992 16:00

#691

Author: Toufik Zoubeidi
Date: Tue, 17 Nov 1992 16:00

43 lines
1358 bytes

Hello, 

In preparing a class example we found out that in computing quartiles
S-plus uses different methods under different commands. The method
used in the commands "summary" or "quantile" is different from the 
one used to compute quartiles for a boxplot in the command "boxplot".
We know which method is used in each case. Does anyone know the reason
for this difference.

Below is the illustration of this

>X      (The data)

  24  11 107  18  29  49  94  12  16  22 141  18  21  13  11

>summary(X)

 Min. 1st Qu. Median  Mean 3rd Qu. Max. 
   11    14.5     21 39.07      39  141

>A <- boxplot(X, plot=F)
>A

$stats:
     [,1] 
[1,]   94
[2,]   49  <-- 3rd Qu. 
[3,]   21  
[4,]   13  <-- 1st Qu.
[5,]   11

$n:
[1] 15


$out:
[1] 107 141  <-- If the quartiles computed in "summary" were used
                 then 94 will also be out. 

$group:
[1] 1 1

Bye, Toufik.

Re: Quartiles in S-plus

#698

Author: Patrick J. Fleury
Date: Thu, 19 Nov 1992 04:19

19 lines
1399 bytes

In article <1992Nov17.170005@masg1.epfl.ch> zoubeidi@masg1.epfl.ch (Toufik Zoubeidi) writes:
>Hello, 
>
>In preparing a class example we found out that in computing quartiles
>S-plus uses different methods under different commands. The method
>used in the commands "summary" or "quantile" is different from the 
>one used to compute quartiles for a boxplot in the command "boxplot".
>We know which method is used in each case. Does anyone know the reason
>for this difference.
>
 There was an informative article a couple of years ago in _The Americna
_Statistician_ which might shed some light on this.  I think it was called
_Some implementations of the boxplot_ and two of its authors were Iglewicz 
and Hoaglin.  I think the year was 1989 but I am not absolutely sure.

As I remember it, the authors point out that there are eight different
definitions of the sample quartile which are used in different circumstances.

It is worth looking at.

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