[R] Constructing bar charts with standard error bars

[Frank E Harrell Jr]

John Zabroski wrote:
> I am new to R.
> 
> I want to graph group data using a "Traditional Bar Chart with Standard
> Error Bar", like the kind shown here:
> http://samiam.colorado.edu/~mcclella/ftep/twoGroups/twoGroupGraphs.html

There are severe problems with dynamite plots such as these.  See 
http://biostat.mc.vanderbilt.edu/DynamitePlots for a list of problems 
and solutions.

Frank

> 
> Is there a simple way to do this?
> 
> So far, I have only figured out how to plot the bars using barplot.
> 
> testdata <- scan(, list(group=0,xbar=0,se=0))
> 400 0.36038 0.02154
> 200 0.35927 0.02167
> 100 0.35925 0.02341
> 50 0.35712 0.01968
> 25 0.35396 0.01931
> 
> barplot(testdata$xbar, names.arg=as.character(testdata$group), main="a=4.0",
> xlab="Group", ylab="xbar")
> xvalues <- c(0.7, 1.9, 3.1, 4.3, 5.5)
> arrows(xvalues, testdata$xbar, xvalues, testdata$xbar+testdata$se, length=
> 0.4, angle=90, code=3)
> 
> 
> The best clue I have so far is Rtips #5.9:
> http://pj.freefaculty.org/R/Rtips.html#5.9 which is what I based my present
> solution off of.
> 
> However, I do not understand how this works.  It seems like there is no
> concrete way to determine the arrow drawing parameters x0 and x1 for a
> barplot.  Moreover, the bars seem to be "cut off".
> 
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> 
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-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University