Thanks for the clarification Dr. Therneau. Until I learn more about this I can at least remember that "plain" is bad.
Thanks, Paul --- On Mon, 4/16/12, Terry Therneau <thern...@mayo.edu> wrote: > From: Terry Therneau <thern...@mayo.edu> > Subject: Re: Kaplan Meier analysis: 95% CI wider in R than in SAS > To: r-help@r-project.org, "Paul Miller" <pjmiller...@yahoo.com> > Received: Monday, April 16, 2012, 8:30 AM > On 04/14/2012 05:00 AM, r-help-requ...@r-project.org > wrote: > > Am replicating in R an analysis I did earlier using > SAS. See this as a test of whether I'm ready to start using > R in my day-to-day work. > > ? > > Just finished replicating a Kaplan Meier analysis. > Everything seems to work out fine except for one thing. The > 95% CI around my estimate for the median is substantially > larger in R than in SAS. For example, in SAS I have a median > of 3.29 with a 95% CI of [1.15, 5.29]. In R, I get a median > of 3.29 with a 95% CI of [1.35,?13.35]. > > ? > > Can anyone tell me why I get this difference? > > > > The confidence interval for the median is based on the > confidence intervals for the curves. There are several > methods for computing confidence intervals for the curves: > plain, log, log-log, or logit scale. There are > opinions on which is best, and it is a close race: except > for the first of these. The type "plain" intervals are > awful, it's like putting me in one lane of a championship > 100 meter dash. > > Until about version 9 the only option in SAS was "plain", > then for a time it was still the default. By 9.2 they > finally went to loglog. > > Terry Therneau > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
