"Geoff Russell" <[EMAIL PROTECTED]> wrote in news:[EMAIL PROTECTED]:
> Dear UseRs, > > Suppose I have data regarding smoking habits of a prospective cohort > and wish to determine the risk ratio of colorectal cancer in the > smokers compared to the non-smokers. What do I do at the end of the > study with people who die of heart disease? Can I just censor them > exactly the same as people who become uncontactable or who die in a > plane crash? If not, why not? > > I'm thinking that heart disease isn't independent of smoking even > though a death from heart disease is probably uninformative about > colorectal cancer risk. Hence,I suspect simply censoring these deaths > will introduce a bias, but I don't know how to correct for it. > This isn't really an R question, of course. Quick answer; don't censor if the subject survives a heart disease event. One is still at risk for colorectal cancer. I am not sure there is a completely correct statitical method for correcting this sort of informative censoring induced by competing risks if your focus is colonic neoplasms. There would also be other cancers (oropharyngeal, laryngeal, lung, kidney, bladder) that would also pose similar potentially informative censoring events, especially if the subject dies, eh. I think you can take solace in that fact that any positive association you find will be an underestimate regarding smoking's induction of colorectal neoplasms. A full treatment might be a Markov model that would allow transitions to "heart disease", "colorectal cancer", "other smoking related cancers" and "death". You can still transition to colorectal cancer after heart disease and I doubt that the risk of colorectal cancer is much changed after making the transition into "heart disease" except for the fact that such subjects will be bombarded by messages to stop smoking. I would predict that one's risk of staying in the surviving risk set would be very much loweer after transitioning to lung or oropharyngeal cancer, however. -- David Winsemius ______________________________________________ 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.
