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2009 Jan 07
0
Frailty by strata interactions in coxph (or coxme)?
...al, receiving Z(k,i) treatment (0-1) in the kth center as: lambda(k,i)=lambda(0,k)*exp(b*Z(k,i)+om(k)*Z(k,i)) where om(k) = center specific effect - mean treatment effect ~ distributed as a (log-) gamma or normal frailty. I coded this model in R as: r1<-coxph(Surv(d,e)~treat*frailty(center)+othercovars+strata(center)) coxph produces a table with the coefficients and standard errors for: a) the treatment variable b) the covariates as well as c) the treatment x frailty interaction effect. but the main effect of frailty is estimated to be zero (which I expected, since it is "absorbed" i...