[R] general question about plotting multiple regression results [Broadcast]

[Liaw, Andy]

I suspect you'll greatly benefit a read of Prof. Fox's book(s) on
regression models, as well as making use of his "car" package.  You may
want to read up on partial residual plots and partial regression plots.

Andy

From: Simon Pickett
> 
> Hi all,
> 
> I have been bumbling around with r for years now and still 
> havent come up with a solution for plotting reliable graphs 
> of relationships from a linear regression.
> 
> Here is an example illustrating my problem
> 
> 1.I do a linear regression as follows
> 
> summary(lm(n.day13~n.day1+ffemale.yell+fmale.yell+fmale.chroma
> ,data=surv))
> 
> which gives some nice sig. results
> 
> Coefficients:
>              Estimate Std. Error t value Pr(>|t|)
> (Intercept)  -0.73917    0.43742  -1.690 0.093069 .
> n.day1        1.00460    0.05369  18.711  < 2e-16 ***
> ffemale.yell  0.22419    0.06251   3.586 0.000449 ***
> fmale.yell    0.25874    0.06925   3.736 0.000262 ***
> fmale.chroma  0.23525    0.11633   2.022 0.044868 *
> 
> 2. I want to plot the effect of "ffemale.yell", "fmale.yell" 
> and "fmale.chroma" on my response variable.
> 
> So, I either plot the raw values (which is fine when there is 
> a very strong relationship) but what if I want to plot the 
> effects from the model?
> 
> In this case I would usually plot the fitted values values 
> against the raw values of x... Is this the right approach?
> 
> fit<-fitted(lm(n.day13~n.day1+ffemale.yell+fmale.yell+fmale.ch
> roma,data=fsurv1))
> 
> plot(fit~ffemale.yell)
> 
> #make a dummy variable across the range of x 
> x<-seq(from=min(fsurv1$ffemale.yell),to=max(fsurv1$ffemale.yel
> l), length=100)
> 
> #get the coefficients and draw the line
> co<-coef(lm(fit~ffemale.yell,data=fsurv1))
> y<-(co[2]*x)+co[1]
> lines(x,y, lwd=2)
> 
> This often does the trick but for some reason, especially 
> when my model has many terms in it or when one of the 
> independent variables is only significant when the other 
> independent variables are in the equation, it gives me strange lines.
> 
> Please can someone show me the light?
> 
> Thanks in advance,
> 
> Simon.
> 
> 
> 
> 
> 
> 
> Simon Pickett
> PhD student
> Centre For Ecology and Conservation
> Tremough Campus
> University of Exeter in Cornwall
> TR109EZ
> Tel 01326371852
> 
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> 


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