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.
