# Re: [R] Impaired boxplot functionality - mean instead of median

From: Michael H. Prager <Mike.Prager_at_noaa.gov>
Date: Fri 02 Dec 2005 - 05:10:43 EST

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:

>
>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
>>
>>Martin Maechler, ETH Zurich
>>
>>
>>
>>
>>>>>>>"Evgeniy" == Evgeniy Kachalin <ka4alin@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.
>>
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>>
>>
>
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```--

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

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