[R] How to plot effect of x1 while controlling for x2

[Greg Snow]

Look at Predict.Plot (and TkPredict) from the TeachingDemos package.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Mark Na
> Sent: Monday, November 15, 2010 2:40 PM
> To: r-help at r-project.org
> Subject: [R] How to plot effect of x1 while controlling for x2
> 
> Hello R-helpers,
> 
> Please see a self-contained example below, in which I attempt to plot
> the effect of x1 on y, while controlling for x2.
> 
> Is there a function that does the same thing, without having to
> specify that x2 should be held at its mean value? It works fine for
> this simple example, but might be cumbersome if the model was more
> complex (e.g., lots of x variables, and/or interactions).
> 
> Many thanks,
> 
> Mark
> 
> 
> #make some random data
> x1<-rnorm(100)
> x2<-rnorm(100,2,1)
> y<-0.75*x1+0.35*x2
> 
> #fit a model
> model1<-lm(y~x1+x2)
> 
> #predict the effect of x1 on y, while controlling for x2
> xv1<-seq(min(x1),max(x1),0.1)
> yhat_x1<-
> predict(model1,list(x1=xv1,x2=rep(mean(x2),length(xv1))),type="response
> ")
> 
> #plot the predicted values
> plot(y~x1,xlim=c(min(x1),max(x1)), ylim=c(min(y),max(y)))
> lines(xv1,yhat_x1)
> 
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