[R] survSplit

[Danardono]

I am just realized that  survival has the facility to do survival time 
splitting survSplit
after read some postings about  time dependency  in the list.
Is it survSplit only for the survival data input (time,status)  and not 
for the 'counting process' input (start,stop,status)?

I take one example modified from the survSplit help:
 >data(aml)
 >aml3<-survSplit(aml,cut=c(5,10,50),end="time",start="start",event="status",episode="i",id="id")

 >coxph(Surv(time,status)~x,data=aml)

                coef exp(coef) se(coef)    z     p
xNonmaintained 0.916       2.5    0.512 1.79 0.074

Likelihood ratio test=3.38  on 1 df, p=0.0658  n= 23

#the same
 >coxph(Surv(time,status)~x,data=aml3)

                coef exp(coef) se(coef)    z     p
xNonmaintained 0.916       2.5    0.512 1.79 0.074

Likelihood ratio test=3.38  on 1 df, p=0.0658  n= 63

BUT If I split aml3 further:

 >aml4<-survSplit(aml3,cut=c(9,12,40),end="time",start="start",event="status",episode="i",id="id2")
#not the same!
 >coxph(Surv(start,time,status)~x,data=aml4)
               coef exp(coef) se(coef)    z     p
xNonmaintained 1.05      2.85    0.515 2.03 0.042

Likelihood ratio test=4.38  on 1 df, p=0.0363  n= 105

This one is corrrect
 >aml5<-survSplit(aml,cut=c(5,9,10,12,40,50),end="time",start="start",event="status")
 > coxph(Surv(start,time,status)~x,data=aml5)
                coef exp(coef) se(coef)    z     p
xNonmaintained 0.916       2.5    0.512 1.79 0.074
Likelihood ratio test=3.38  on 1 df, p=0.0658  n= 103

It would be useful to modify survSplit to accomodate counting process 
input as well.

Thanks
Danar
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Department of Statistics          
Umeå University                  
SE-90187 Umeå, Sweden