## Somewhat unrealistic example of nonresponse bias.
data(pbc, package="survival")
biasmodel<-glm(I(trt>0)~age*edema,data=pbc)
pbc$randprob<-fitted(biasmodel)
dpbc<-svydesign(id=~1, prob=~randprob, strata=~edema, data=subset(pbc,trt>0))
rpbc<-as.svrepdesign(dpbc)
svycoxph(Surv(time,status)~log(bili)+protime+alb,design=dpbc)
svycoxph(Surv(time,status)~log(bili)+protime+alb,design=rpbc)
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