[Rd] box and whisker (PR#13821)

[m.crawley at imperial.ac.uk]

In a Box and Whisker plot, I thought that when there are outliers both abov=
e and below the whiskers, then the whiskers should both be the same length =
(plus or minus 1.5 times the inter-quartile range).

If you look at the plot for SilwoodWeather on p.155 of The R Book you will =
see that for November (month =3D 11) the upper whisker is shorter than the =
lower, while for other months with outliers both above and below, the lines=
 are the same lengths.

When there are no outliers, then of course the maximum and minimum values r=
esult in whiskers of different lengths above and below.

Here is the code that creates the problem:

data<-read.table("c:\\temp\\SilwoodWeather.txt",header=3DT)
attach(data)
names(data)

[1] "upper" "lower" "rain"  "month" "yr"

month<-factor(month)
plot(month,upper)

and exactly the same with

boxplot(upper~month)



Best wishes,

Mick

Prof  M.J. Crawley  FRS

Imperial College London
Silwood Park
Ascot
Berks
SL5 7PY
UK

Phone (0) 207 5942 216
Fax     (0) 207 5942 339


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