[R] Adding error bars to xyplot()

[David Winsemius]

On Apr 21, 2010, at 6:24 PM, Jon Zadra wrote:

> Hi,
>
> I want to add error bars to a plot generated with xyplot.  I've  
> tried both errbar() and plotCI(), but in both cases the points are  
> not in the same place.  It's as if the two functions are using a  
> different frame of reference for the plotting area.

Yes. plotCI uses base graphics while xyplot is a lattice function.

>
> for example:
> means <- c(92.5, 92.25, 90.9, 91.0, 94.15, 90.05) #means
> time <- c(1,1,2,2,3,3) #occasion variable
> group <- rep(c("n","u"),3) #grouping variable
> SE <- c(2.22, 1.66, 2.10, 1.43, 2.31, 1.57) #standard errors
>
> #Plot the graph
> xyplot(means ~ time, groups=group, type="o", lwd=3, main="Change  
> Over Time by Condition", scale=list(cex=2), xlab="Test Number",  
> auto.key=T)
>
> #first attempt
> require(Hmisc)
> errbar(x = time, y = means, yplus = means + SE, yminus = means - SE,  
> add=T, col=c("blue", "hotpink"))

A base graphics function.
>
> #second attempt, same result
> require(gplots)
> plotCI(x = time, y = means, uiw = SE, add=T)

Another base graphics function.

Since you already have Hmisc why not check out Harrell's xYplot which  
provides CI's in a grid function:
 From the xYplot examples:

require(Hmisc)
dfr <- expand.grid(month=1:12, continent=c('Europe','USA'),
  sex=c('female','male')) set.seed(1)
dfr <- upData(dfr, y=month/10 + 1*(sex=='female') +
                           2*(continent=='Europe') +
                           runif(48,-.15,.15),
                    lower=y - runif(48,.05,.15),
                    upper=y + runif(48,.05,.15))
xYplot(Cbind(y,lower,upper) ~ month|continent,  
subset=sex=='male',data=dfr)
>
>
> Thanks in advance!
>
> - Jon
>
> -- 
> Jon Zadra
> Department of Psychology
> University of Virginia
> P.O. Box 400400
> Charlottesville VA 22904
> (434) 982-4744
> email: zadra at virginia.edu
> <http://www.google.com/calendar/embed?src=jzadra%40gmail.com>
>
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David Winsemius, MD
West Hartford, CT