beginner's question: Graphical presentation of t test

Take a look at the 'plotmeans' function in the gregmisc library.  It will
draw the means and error bars for you, allowing you to connect the means for
the paired control and treated groups with something like this:

<R code>
# sample source data 10 replicates for each enzyme for treated and control
x <- rnorm(60)
enzyme <- rep(c("ABC123", "ABD124", "CCF342"), length=60)
treat  <- rep(c("CONTROL","TREATED"), length=60)

# create a enzyme by treatment label
group <- interaction(enzyme, treat)

# plot the means and confidence intervals
library(gregmisc)
plotmeans( x ~ group, connect=list(1:2,3:4,5:6))

# add p-values
data <- data.frame(x, enzyme, treat)
p.vals <- by( data, enzyme, function(data) t.test( x ~ treat,
data=data)$p.value )
text(x=c(1.5, 3.5, 5.5), y=rep(0,3), paste("P-value:\n",
format.pval(p.vals)) )
</R code>
 
-Greg

-----Original Message-----
From: Peter.Robinson at t-online.de [mailto:Peter.Robinson at t-online.de]
Sent: Saturday, June 07, 2003 1:43 PM
To: r-help at stat.math.ethz.ch
Subject: [R] beginner's question: Graphical presentation of t test


Hi,

Is there any way to use R to present t test results for three 
groups of 
experiments, each of which involves several parallel 
experiment series with 
groups of control vs treated. I would like to present the 
average fold change 
of the experimental parameter (concentration of enzymes) as bars with 
standard error and the p value above the bar. So, there 
should be two groups 
(control vs treated)  of three bars for the three enzymes.

Thanks

Peter

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