[R] Impaired boxplot functionality - mean instead of median

[P Ehlers]

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.
> 
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