Hi Robert,
Your points are well taken. However, I reserve mine, b/c I think without this
detailed discussion, an average R user would simply confused the "interquartile
range" said in boxplot help file with the results of "IQR". Changing it to
"length of box" makes it more exact and consistent, as I stated earlier. With
all these being said, this is up to the R core team to decide.
...Tao
----- Original Message ----
> From: Robert Baer <rb...@atsu.edu>
> To: "Shi, Tao" <shida...@yahoo.com>; Peter Ehlers <ehl...@ucalgary.ca>
> Cc: R Project Help <R-help@r-project.org>
> Sent: Thu, May 13, 2010 7:25:09 AM
> Subject: Re: [R] Whiskers on the default boxplot {graphics}
>
> > Hi Peter,
>
> You're absolutely correct! The description
> for 'range' in 'boxplot' help file is a little bit confusing by using the
> words
> "interquartile range". I think it should be changed to the "length of the
> box"
> to be exact and consistent with those in the help file for
> "boxplot.stats".
The issue is probably that there are multiple ways (9 to
> be exact) of defining quantiles in R. See 'type= ' arguement for
> ?quantile. The quantile function uses type=7 by default which matches the
> quantile definition used by S-Plus(?), but differs from that used by SPSS.
> Doesn't fivenum essentially use the equivalent of a different "type= "
> arguement
> (maybe 2 or 5) in constructing the hinges?
It seems perfectly reasonable
> to talk about 'length of box' (or 'box height' depending how you display the
> boxplot), but aren't the hinges simply Q1 and Q3 defined by one of the
> possible
> quartile definitions (as Peter points out the one used by fivenum)? The
> box height does not necesarily match the distance produced by IQR() which
> also
> seems to use the equivalent of quantile(..., type=7), but it is still an IQR,
> is
> it not?
Quantiles apparantly can be defined in more than one "acceptable"
> way (sort of like dealing with ties in rank statistics). The OP seemed to
> want an "exact" explanation of the wiskers, and I think Peter has pointed us
> at
> the definition of quartiles used by fivenum, as opposed to the default
> used with quantile(..., "type=7").
All that said, I'm not convinced that
> it is wrong to speak of "interquartile range" in 'boxplot'
> help.
Rob
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