[R] help understanding box plots

[Jay Pfaffman]

Another naive stats question.  I'm trying to better understand what
boxplots are telling me.  

I think what I see is the median and the boundaries of the 1st and 3rd
quartiles.  The whiskers represent the range of the data unless there
are points which are outside "range" (default: 1.5) times the distance
from the median to that quartile.  Is that right?  I've read the
documentation for boxplot numerous times, but don't quite understand
it well enough to communicate it to my professor who's helping me with
this project.  (You'll be relieved to know that neither of us fancies
ourself a statistician!)

V&R (p. 122) claims that the hinges are "roughly quartiles," so
perhaps my naive understanding is close enough.

I've got a relatively small data set (n~=12).  I think it would help
to see the data points plotted on top of the boxplots.  Here's what
I'm doing now:

    par(las=2,ps=14,mar=c(15, 4, 4, 2))
    boxplot(split(ranks,c(1:25)), names=items, notch=T, horizontal=F, add=F)

If I could get the points of each of the 25 variables plotted on top
of the box, that'd be great.

Thanks as always.

-- 
Jay Pfaffman                           pfaffman at relaxpc.com
+1-415-821-7507 (H)                    +1-415-810-2238 (M)
http://relax.ltc.vanderbilt.edu/~pfaffman/
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