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Showing which bars in a bar chart are significantly different

5 messages · omernevo, Sarah Goslee, Joshua Wiley +1 more

Original
omernevo
# 
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
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?

Thanks a lot!
Omer

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Sarah Goslee
# 
I'd do it by hand with either segments() or arrows() and text(), but
without a reproducible example I can't give you specific instructions.

Sarah
On Wed, Jul 6, 2011 at 4:37 PM, omernevo <nevo84 at gmail.com> wrote:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Joshua Wiley
    

    

      
      #
    

  


  

      
On Wed, Jul 6, 2011 at 1:37 PM, omernevo <nevo84 at gmail.com> wrote:

            

      
      
      
    

        
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.

            

      
      
      
    

        
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

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      John Kane
    

    

      
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# Incremental approach 
bb <- c(23, 45, 67)
bsp  <- barplot(bb,beside=TRUE) # get midpoints of the bars and plot

# draw lines
segments( .7, 50, 1.9, 50)
segments(.7, 50, .7, 48)
segments(1.9, 50, 1.9, 48)

# Or all in one go

segments(c(.7, .7, 1.9), c(50,50,50), c(1.9,.7,1.9), c(50, 48, 48))

        
--- On Wed, 7/6/11, omernevo <nevo84 at gmail.com> wrote: