[R] How do I specify a partially completed survival analysis model?

[David Winsemius]

On Nov 20, 2009, at 9:46 AM, RWilliam wrote:

>
> Sorry for being impatient but is there really no way of doing this  
> at all?
> It's quite urgent so any help is very much appreciated. Thank you.
>

The general method with glm's to specify a model with fixed  
coefficients is to use an offset. I believe that the coxph function  
also has that facility and seem to remember that Therneau uses offsets  
in some of the examples he offers in his books and technical reports.

Perhaps:
cmod <- coxph( Surv(Time,Censor)~X1, offset=4.3*X2, data= <dfname>  )

Further requests about specifics should be accompanied (as suggested  
by the Posting Guide) by some code that sets up a reproducible example.

-- 
David.
>
>
> RWilliam wrote:
>>
>> Hello,
>>
>> I just started using R to do epidemiologic simulation research  
>> using the
>> Cox proportional hazard model. I have 2 covariates X1 and X2 which  
>> I want
>> to model as h(t,X)=h0(t)*exp(b1*X1+b2*X2). I assume independence of  
>> X from
>> t.
>>
>> After I simulate Time and Censor data vectors denoting the  
>> censoring time
>> and status respectively, I can call the following function to fit  
>> the data
>> into the Cox model (a is a data.frame containing 4 columns X1, X2,  
>> Time
>> and Censor):
>> b = coxph (Surv (Time, Censor) ~ X1 + X2, data = a, method =  
>> "breslow");
>>
>> Now the purpose of me doing simulation is that I have another  
>> mechanism to
>> generate the number b2. From the given b2 (say it's 4.3), Cox model  
>> can be
>> fit to generate b1 and check how feasible the new model is. Thus, my
>> question is, how do I specify such a model that is partially  
>> completed (as
>> in b2 is known). I tried things like Surv(Time,Censor)~X1+4.3*X2,  
>> but it's
>> not working. Thanks very much.
>>
>
> -- 
> View this message in context: http://old.nabble.com/How-do-I-specify-a-partially-completed-survival-analysis-model--tp26421391p26441878.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT