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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