[R] Showing which bars in a bar chart are significantly different

[Joshua Wiley]

On Wed, Jul 6, 2011 at 1:37 PM, omernevo <nevo84 at gmail.com> wrote:
> Hello,
>
> a probably rather stupid question to which I can't find an answer:
>
> I have a bar chart, and I want to present which bars are significantly
> different by placing a line with an asterisk above then (similarly to fig. 3

I would highly recommend some reading about data visualizations
techniques (and while you're at it, something on significance
testing).  Here are two:

http://www.b-eye-network.com/view/2468
http://biostat.mc.vanderbilt.edu/wiki/Main/DynamitePlots

I would argue for a paradigm switch.

> in: http://jnm.snmjournals.org/content/46/4/574.figures-only).
>
> Does anyone have a reference where can I find some instructions how to learn
> this?

I don't know of an automated way off hand.  But, if you assign the
results of barplot() (I am assuming you are using traditional
graphics),

tmp <- barplot(rnorm(20))

tmp # has the locations on the x axis for each bar

now you could go to town with lines() (see ?lines for documentation)
to get those bracket thingies and text() to add the asterisks and
labels.  Alternately, you could add asterisks and such just using
points()

points(x, y, pch = "*")

where x and y are the coordinates where you want the * placed.

Good luck,

Josh

>
> Thanks a lot!
> Omer
>
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-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
https://joshuawiley.com/