[R] Force regression line to a 1:1 relationship

[John Fox]

Dear Ross,

lm(y ~ 0 + offset(x)) will do the trick, but the resulting model has no
coefficient estimates and thus can't be used with abline(). You can, e.g.,
get predictions from the model, but I'm not sure what real use it will be to
you.

I hope this helps,
 John

--------------------------------
John Fox
Senator William McMaster
  Professor of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
http://socserv.mcmaster.ca/jfox



> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of RCulloch
> Sent: September-13-11 7:03 AM
> To: r-help at r-project.org
> Subject: [R] Force regression line to a 1:1 relationship
> 
> Hello,
> 
> I appreciate this is likely to be an easy question. I am trying to
> obtain the residuals from a linear regression where the line is forced
> to have a
> 1:1 relationship.
> 
> An example of the data:
> 
> A<-c(0.9803922, 1.3850416, 0.8241758, 0.0000000, 0.4672897, 1.1904762,
> 0.0000000, 0.9456265,
> 1.5151515)
> B<-c(1.3229572, 1.9471488, 1.3182674, 0.7007708, 1.0185740, 1.0268562,
> 0.8695652, 0.3016591, 1.9667171)
> 
> plot(A, B, ylim=c(0,2), xlim=c(0,2))
> abline(0,1, col="lightgrey", lty="dashed",lwd=2)#1:1 relationship =
> what I want to use in the lm()
> 
> #Normal regression
> AB<-lm(A~B)
> 
> #plot regression line
> abline(lm(AB))
> 
> 
> How can I force the regression to have a 1:1 relationship, I assume it
> is to do with offset() but I have somewhat fried my brain trying
> numerous variations and I am not convinced any are correct. I was also
> hoping the plot function would show me that the calculation is correct,
> but any time I use the offset() command there is no line plotted?
> 
> Any hints or tips would be much appreciated!
> 
> Ross
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Force-
> regression-line-to-a-1-1-relationship-tp3809733p3809733.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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