R Under development (unstable) (2024-06-02 r86665 ucrt) -- "Unsuffered Consequences"
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> library(survival)
> #
> # Check out the Dory&Korn confidence interval option
> #
> tdata <- data.frame(time= 1:10,
+                     status=c(1,0,1,0,1,0,0,0,1,0))
> 
> fit1 <- survfit(Surv(time, status) ~1, tdata, conf.lower='modified')
> fit2 <- survfit(Surv(time, status) ~1, tdata)
> 
> stdlow <- fit2$std.err * sqrt(c(1, 10/9, 1, 8/7, 1, 6/5, 6/4, 6/3, 1, 2/1))
> lower <- exp(log(fit2$surv) - qnorm(.975)*stdlow)
> all.equal(fit1$lower, lower, check.attributes=FALSE)
[1] TRUE
> 
> proc.time()
   user  system elapsed 
   0.76    0.07    0.82