Dear useRs,
I'm trying to estimate the proportion of individuals with a without a certain
recurring ailment at several times points. The data are of the survival type,
with "start"-"stop" dates and whether the individual had the ailment in that
interval.
Some cases are observed until database closure and some died or are lost to
followup. The interest is not on death. I have tries using "coxph" and "cph" as
fitCOXPH <-
coxph(Surv(time=start,time2=stop,sick)~strata(adult)+frailty(individual),data=test.data)
fitKM <- survfit(fitCOXPH )
summary(fitKM ,times=sort(seq(0,128,by=16)))
What I noted is that the proportion was decreasing with increasing time, which
I felt was incorrect!
I then tried estimating the number without the ailment in each discrete month,
but computing the denominator (the number alive and at risk) and getting the
confidence intervals becomes a huge undertaking. As an approximation I tend to
use the number who survive to the midpoint of the month resulting in
proportions above 1 sometimes, for instance at the beginning where no
individuals have the ailment but some are censored before the midpoint time.
I have reason to believe there is a way within the survival packages but
haven't figured out how.
Thanking you in advance, Vumani
ps: sorry for cross posting. wasnt sure whether "[EMAIL PROTECTED]" or
"r-help@R-project.org" was more suitable for this question
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