Message-ID: <82F3AF5D-928A-4925-BDD1-98334A60856C@comcast.net>
Date: 2013-03-15T04:04:50Z
From: David Winsemius
Subject: cnfidence intervals for survfit()
In-Reply-To: <1363297789.26448.YahooMailNeo@web122902.mail.ne1.yahoo.com>
Sent from my iPhone
On Mar 14, 2013, at 2:49 PM, array chip <arrayprofile at yahoo.com> wrote:
> 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:
That's not my understanding. I would have expected the estimates to be on a log-hazard scale ( continuous expression: log(deltaS/deltaT/S) )
>
> 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
>
> [[alternative HTML version deleted]]
>
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