[R] Impaired boxplot functionality - mean instead of median

Michael H. Prager Mike.Prager at noaa.gov
Thu Dec 1 19:10:43 CET 2005


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."


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.
>>R-help at stat.math.ethz.ch mailing list
>>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>R-help at stat.math.ethz.ch mailing list
>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html


Michael Prager, Ph.D.
Population Dynamics Team, NMFS SE Fisheries Science Center
NOAA Center for Coastal Fisheries and Habitat Research
Beaufort, North Carolina  28516
Opinions expressed are personal, not official.  No
government endorsement of any product is made or implied.

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