R help - May 2010 - Nomogram with multiple interactions (package rms)

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 ?

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

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

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