Hi, I am wondering how the confidence interval for Kaplan-Meier estimator is
calculated by survfit(). For example,
> summary(survfit(Surv(time,status)~1,data),times=10)
Call: survfit(formula = Surv(rtime10, rstat10) ~ 1, data = mgi)
time n.risk n.event survival std.err lower 95% CI upper 95% CI
10 168 55 0.761 0.0282 0.707 0.818
I am trying to reproduce the upper and lower CI by using standard error. As far
I understand, the default method for survfit() to calculate confidence interval
is on the log survival scale, so:
upper CI = exp(log(0.761)+qnorm(0.975)*0.0282) = 0.804
lower CI = exp(log(0.761)-qnorm(0.975)*0.0282) = 0.720
they are not the same as the output from survfit().
Am I missing something?
Thanks
John
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