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

David Winsemius dwinsemius at comcast.net
Tue Sep 13 17:44:46 CEST 2011

On Sep 13, 2011, at 9:43 AM, RCulloch wrote:

> Dear John,
> Thank you for that, and for explaining why the abline() command wont/ 
> dosen't
> work. The approach is based on reviewers comments that I am a tad  
> sceptical
> about myself but yet curious enough to test their suggestion......I  
> don't
> think it is very straightforward to explain; however, it involves  
> using the
> residuals of the lm() and plotting them against a covariate to assess
> whether or not the deviation from the 1:1 relationship is in someway
> influenced by the other covariate. I hope that shines a small amount  
> of
> light on this rather unorthodox approach?!

Plotting the residuals against a covariate is a standard way to assess  
the assumption that the residuals are distributed normally around each  
continuous regressor and have no non-linear relationship around each  
continuous regressor. It is not to assess a "1:1 relationship",  
whatever that is. I think we would need to  see a complete quotation  
of the reviewer's comments before deciding who is confused in this  

David Winsemius, MD
West Hartford, CT

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