> I thought about this some more, and I'm not sure that possibility is > "to blame." In my time-dependent model, I don't think I'm doing > anything different than is done for transplant in the Stanford > Heart Study (the often used example for this kind of time-dependent > covariate). As in my case, you would not transplant a dead patient. > So, I remain puzzled as to why my model is misbehaving.
The Stanford Heart Study, quoted in nearly every survival book as you say, is a bit of an anomaly. At the time it was run a good tissue match between the donor heart and the recipient was considered very important. When a donor became available, the best match (or near best) among those waiting was chosen to recieve it. Since the donor genetics are unpredictable, this is essentially equal to a random pick from those waiting. The Stanford study is nearly alone in examples of time-dependent treatment in not having selection effects. Terry T. ______________________________________________ R-help@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.