[R] Nomogram with multiple interactions (package rms)

[Frank E Harrell Jr]

On 05/19/2010 03:17 PM, Marc Carpentier wrote:
> Dear list, I'm facing the following problem : A cox model with my sex
> variable interacting with several continuous variables :
> cph(S~sex*(x1+x2+x3)) And I'd like to make a nomogram. I know it's a
> bit tricky and one mights argue that nomogram is not a good a
> choice... I could use the parameter
> interact=list(sex=("male","female"),x1=c(a,b,c))... but with rcs or
> pol transformations of x1, x2 and x3, the choice of the
> categorization (a,b,c,...) is arbitrary and the nomogram not so
> useful... Considering that sex is the problem, I thought I could draw
> two nomograms, one for each sex... based on one model. These would be
> great. Do you think it's possible ?

Yes, you can specify constant predictors not to draw with the omit= 
argument.  But try first to draw everything.  Shouldn't you just get 2 
axes each for x1 x2 x3?

>
> Taking the exemple of the help of nomogram() (package "rms") : f<-
> psm(Surv(d.time,death) ~ sex*age, dist=if(.R.)'lognormal' else
> 'gaussian')

Drop the if(.R.) which was just corrected in the documentation.  Use 
dist='lognormal'

Frank

>
> Let's add the previously defined blood.pressure effect with an
> interaction with sex too (with cph) : f2<- cph(Surv(d.time,death) ~
> sex*(age+blood.pressure))
>
> I thought of the parameter adt.to : plot(nomorgam(f2,
> adj.to=list(sex="male")) #and "female" for the other one
>
> But nomogram() still wants me to define interact=list(...) Thanks for
> any advice you might have (with adj.to or any alternative...)
>
> Marc Carpentier
>


-- 
Frank E Harrell Jr   Professor and Chairman        School of Medicine
                      Department of Biostatistics   Vanderbilt University