[R] help with Box plot

[David Winsemius]

On Jan 27, 2012, at 9:47 AM, gianni lavaredo wrote:

> Dear researchers
>
> I wish to plot a box plot without the mean line

It's not at the mean.

> (the black line) and the i
> wish a full line for the standard deviation

And the boxplot whiskers are not at the standard deviations, either.  
It is a non-parametric plot.

?boxplot
?boxplot.stats
?fivenum

There are many requests over the years from people with varying  
degrees of knowledge about what box-and-whisker plots really are ....  
and with posted responses  to requests for plotting results that meet  
their desired preconceptions about what boxplots should be (but  
aren't). You should exercise (or build) your searching skills. (This  
is practically a plotting FAQ.)

>
> This is an example
>
> mytest <-  
> c(2.1,2.6,2.7,3.2,4.1,4.3,5.2,5.1,4.8,1.8,1.4,2.5,2.7,3.1,2.6,2.8)
> boxplot(mytest)
>
Try putting in a large number in that vector, say a single 500, print  
the mean and standard deviations and then  see what happens to the   
boxplot. It won't be as you expect.

-- 

David Winsemius, MD
West Hartford, CT