Impaired boxplot functionality - mean instead of median

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch 
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
Michael H. Prager
Sent: Thursday, December 01, 2005 10:11 AM
To: r-help at stat.math.ethz.ch
Subject: Re: [R] Impaired boxplot functionality - mean 
instead of median

All--

Would someone kindly post the reference to Tukey's formula 
for a boxplot 
without whiskers?

I am looking at his book "Exploratory Data Analysis" from 1977.  The 
index includes "box-and-whisker" plot but not "boxplot."  On 
page 39-40 
construction of the plot is described, including the statements: "We 
draw a long, thinnish box that stretches from hinge to hinge, 
crossing 
it with a bar at the median.  Then we draw a 'whisker' from 
each end of 
the box to the corresponding extreme."

MHP


on 12/1/2005 11:57 AM P Ehlers said the following:

I'd like to add two comments to Martin's sensible response.

1. I've seen several intro-stats textbooks that define a
boxplot to have whiskers to the extreme data values
and then define Tukey's boxplot as a "modified" boxplot.
I wish authors wouldn't do that.

2. I've also seen boxplots used for sample sizes as small
as -- are you ready for it? -- n = 2!! (Admittedly, only in
plots comparing several groups.) The help page for
stripchart() points out that stripcharts "are a good
alternative to boxplots when sample sizes are small".
My own rule-of-thumb: n > 20 for single boxplots, n > 12
for multiple boxplots.

Peter Ehlers

Martin Maechler wrote:

 

Boxplots were invented by John W. Tukey and I think should be
counted among the top "small but smart" achievements from the
20th century.  Very wisely he did *not* use mean and 

standard deviations.

Even though it's possible to draw boxplots that are not boxplots
(and people only recently explained how to do this with R on this
mailing list), I'm arguing very strongly against this.

If I see a boxplot - I'd want it to be a boxplot and not have
the silly (please excuse)  10%--------90% whiskers  which
declare 20% of the points as outliers {in the boxplot sense}.

If you want the mean +/- sd plot, do *not* misuse boxplots
for them, please! 

Martin Maechler, ETH Zurich


   

"Evgeniy" == Evgeniy Kachalin <ka4alin at yandex.ru>
  on Thu, 01 Dec 2005 19:04:47 +0300 writes:
             

   Evgeniy> Hello to all users and wizards.
   Evgeniy> I am regulary using 'boxplot' function or its 

analogue - 'bwplot' from 

   Evgeniy> the 'lattice' library. 

[there's the lattice *package*  !]

   Evgeniy> But they are, as far as I understand, totally 
   Evgeniy> flawed in functionality: they miss ability to 

select what they would 

   Evgeniy> draw 'in the middle' - median, mean. What the 

box means - standard 

   Evgeniy> error, 90% or something else. What the 

whiskers mean - 100%, 99% or 

   Evgeniy> something else.
   Evgeniy> Is there any way to realize it? Or is there 

any other good data 

   Evgeniy> visualization function for comparing means of 

various data groups? 

   Evgeniy> Ideally I would like to have a bit more 

customised function for doing 

   Evgeniy> that. For example, 'boxplot(a~b,data=d,mid='mean').


   Evgeniy> -- 
   Evgeniy> Evgeniy, ICQ 38317310.