On Dec 10, 2010, at 2:07 PM, Andreas Wittmann wrote:
Dear R users,
i try to calculate the probabilty to survive a given time by using
the estimated survival curve by kaplan meier.
What is the right way to do that? as far as is see i cannot use the
predict-methods from the survival package?
library(survival)
set.seed(1)
time <- cumsum(rexp(1000)/10)
status <- rbinom(1000, 1, 0.5)
## kaplan meier estimates
fit <- survfit(Surv(time, status) ~ 1)
s <- summary(fit)
## 1. possibility to get the probability for surviving 20 units of
time
ind <- findInterval(20, s$time)
cbind(s$surv[ind], s$time[ind])
See if this helps:
> head(which(s$surv < 0.5))
[1] 368 369 370 371 372 373
> plot(fit)
> abline(h=0.5)
> abline(v=s$time[368])
## 2. possibility to get the probability for surviving 20 units of
time
ind <- s$time >= 20
sum(ind) / length(ind)
--
David Winsemius, MD
West Hartford, CT
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