On May 11, 2010, at 10:35 PM, Jason Rupert wrote:
Humm....Maybe I need to look some place else than boxplot.stats
{grDevices} for a definition of how the upper/lower whiskers are
produced.
By any chance are they "the lowest datum still within 1.5 IQR of the
lower quartile, and the highest datum still within 1.5 IQR of the
upper quartile"?
None of the links from boxplot.stats {grDevices} seemed to reveal
the secret definition of the R whiskers.
You didn't need to go to any other pages. You just needed to read
boxplot.stats ... apparently more than once.
--
David.
Thanks again.
----- Original Message ----
From: Jason Rupert <jasonkrup...@yahoo.com>
To: David Winsemius <dwinsem...@comcast.net>
Cc: R Project Help <R-help@r-project.org>
Sent: Tue, May 11, 2010 9:26:25 PM
Subject: Re: [R] Whiskers on the default boxplot {graphics}
Wowzers...
From ?boxplot.stats:
Details
The two ‘hinges’ are versions of the first and third quartile, i.e.,
close to quantile(x, c(1,3)/4). The hinges equal the quartiles for
odd n (where n <- length(x)) and differ for even n. Whereas the
quartiles only equal observations for n %% 4 == 1 (n = 1 mod 4), the
hinges do so additionally for n %% 4 == 2 (n = 2 mod 4), and are in
the middle of two observations otherwise.
The notches (if requested) extend to +/-1.58 IQR/sqrt(n). This seems
to be based on the same calculations as the formula with 1.57 in
Chambers et al. (1983, p. 62), given in McGill et al. (1978, p. 16).
They are based on asymptotic normality of the median and roughly
equal sample sizes for the two medians being compared, and are said
to be rather insensitive to the underlying distributions of the
samples. The idea appears to be to give roughly a 95% confidence
interval for the difference in two medians.
Is a notch equal to the upper/lower whisker? Is this just a
difference of terminology or something?
Thanks again for all the insights.
----- Original Message ----
From: David Winsemius <dwinsem...@comcast.net>
To: Jason Rupert <jasonkrup...@yahoo.com>
Cc: R Project Help <R-help@r-project.org>
Sent: Tue, May 11, 2010 9:00:15 PM
Subject: Re: [R] Whiskers on the default boxplot {graphics}
On May 11, 2010, at 9:45 PM, Jason Rupert wrote:
How are the lower/upper whiskers defined in the default version of
boxplot {graphics}?
I tried help(boxplot) and searching www.rseek.org, but I was unable
to determine an absolute answer.
You need to follow the links from the help pages and tin this case
it appears that you did not follow the one to
?boxplot.stats
I checked out the definition of boxplot according to Wikipedia (http://en.wikipedia.org/wiki/Box_plot
), but it also had several approaches
listed for how the whiskers could be determined, so I'm just
curious how the default
boxplot {graphics} does it.
Thanks for any feedback
Follow links with the R help system.
and insights.
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
