R help - May 2011 - coxph and survfit issue - strata

Dear users,

In a study with recurrent events: 
My objective is to get estimates of survival (obtained through a Cox model) by
rank of recurrence and by treatment group.
With the following code (corresponding to a model with a global effect of the
treatment=rx), I get no error and manage to obtain what I want :
data<-(bladder)
model1<-coxph(Surv(stop,event)~rx+strata(enum)+cluster(id),data=bladder)
data1<-data.frame(rx=1)
survfit(model1,newdata=data1)

But with the model with strata by treatment interaction (corresponding to a
model with an effect of the treatment by rank), I get the following error:
model2<-coxph(Surv(stop,event)~rx*strata(enum)+cluster(id),data=bladder)

data1<-data.frame(rx=1)

survfit(model2,newdata=data1)
Erreur dans strata(enum) : objet "enum" non trouvé =>error in
strata(enum) : object "enum" not found

Would you have any idea to help me?

Thanks in advance,

Eva




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On May 6, 2011, at 6:22 PM, Eva Bouguen wrote:
> Dear users,
>
> In a study with recurrent events:
> My objective is to get estimates of survival (obtained through a Cox  
> model) by rank of recurrence and by treatment group.
> With the following code (corresponding to a model with a global  
> effect of the treatment=rx), I get no error and manage to obtain  
> what I want :
> data<-(bladder)
> model1<-coxph(Surv(stop,event)~rx+strata(enum) 
> +cluster(id),data=bladder)
> data1<-data.frame(rx=1)
> survfit(model1,newdata=data1)
>
> But with the model with strata by treatment interaction  
> (corresponding to a model with an effect of the treatment by rank),  
> I get the following error:
> model2<-coxph(Surv(stop,event)~rx*strata(enum) 
> +cluster(id),data=bladder)
>
> data1<-data.frame(rx=1)
>
> survfit(model2,newdata=data1)
> Erreur dans strata(enum) : objet "enum" non trouv? =>error in
> strata(enum) : object "enum" not found
Right. Looks like a perfectly clear error message to me .... you  
created a newdata dataframe that did not have all the necessary  
columns that you used on the RHS of your formula.

-- 

David Winsemius, MD
West Hartford, CT

> Dear users,
>
> In a study with recurrent events:
> My objective is to get estimates of survival (obtained through a Cox  
> model) by rank of recurrence and by treatment group.
> With the following code (corresponding to a model with a global  
> effect of the treatment=rx), I get no error and manage to obtain  
> what I want :
> data<-(bladder)
> model1<-coxph(Surv(stop,event)~rx+strata(enum) 
> +cluster(id),data=bladder)
> data1<-data.frame(rx=1)
> survfit(model1,newdata=data1)
>
> But with the model with strata by treatment interaction  
> (corresponding to a model with an effect of the treatment by rank),  
> I get the following error:
> model2<-coxph(Surv(stop,event)~rx*strata(enum) 
> +cluster(id),data=bladder)
>
> data1<-data.frame(rx=1)
>
> survfit(model2,newdata=data1)
> Erreur dans strata(enum) : objet "enum" non trouv? =>error in
> strata(enum) : object "enum" not found
 You have neglected to tell us what version of R and of the survival
library you are using.  (As the author, I always have the newest version
of course.)

  The example you gave works if there is no "cluster" statement.  Your
error is a surprise to me and I will look into it.

 Terry Therneau