[R] Odds ratios from lrm plot

David Winsemius dwinsemius at comcast.net
Sat Nov 12 03:57:47 CET 2011

On Nov 11, 2011, at 9:08 PM, RD235 wrote:

> The code
> library(Design)
> f <- lrm(y~x1+x2+x1*x2, data=data)
> plot(f)
> produces a plot of log odds vs x2 with 0.95 confidence intervals.  
> How do I
> get a plot of odds ratios vs x2 instead?

You would construct a dataset that had selected combinations of x1 and  
x2 and then plot the "response".

It's been a couple of years since I used Design. Harrell migrated to  
lattice plots when he upgraded to 'rms' and changed the Predict/plot  
interface a bit. In the new version it might  something like  
plot(predict(f, x1=seq( ...), x2=c(1,2), type= "fitted"), deopending  
on teh data arrangement.  Why don't you look more closely at the help  
page for `lrm` and work through the examples. At least in the current  
'rms' version there is more than one worked example, and I'm pretty  
sure there were one in Design before that.


David Winsemius, MD
West Hartford, CT

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