[R] Summary vs fivenum results for Q3

[Thomas Lumley]

On Tue, 9 Oct 2007, Schaefer, Robert L. Dr. wrote:

> I've just started using R and am still a neophyte, but I found the 
> following curious result.  I'm using the current version of R (2.5.1 
> (2007-06-27) ).
>
> Why are the results for the third quartile different in the output from 
> the summary and fivenum commands?

Because there are lots of ways to define quantiles.  The quantile() 
function provides 9 definitions of quantiles, and in your data these range 
from 913 to 1015.75

You might also get a hint that there are deliberately different 
definitions involved from the help page for fivenum(), which doesn't use 
the word "quartile" at all.

Everyone agrees that the third quartile (and the upper hinge)  should be 
somewhere between the 24th and 25th of 32 observations, but not on which 
point in this interval should be chosen.

 	-thomas


Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle