Hello @daveconifer1 and welcome to the SAS Support Communities!
I've just seen that @unison was faster in answering your question (while I was writing the text below), so this is rather a confirmation of what he has written ...
As far as I know, this refers to the 1982 article by R. Brookmeyer and J. Crowley "A Confidence Interval for the Median Survival Time" in Biometrics (see the reference in the PROC LIFETEST documentation). This confidence interval (and the corresponding CIs for the other two quartiles) are available in ODS table Quartiles of PROC LIFETEST.
I think for the original CI as per Brookmeyer and Crowley you need to specify the option CONFTYPE=LINEAR in the PROC LIFETEST statement because the default has been changed to CONFTYPE=LOGLOG in SAS version 9.1, but this is rather based on a generalization of the original CI. The formula and more details can be found in section "Breslow, Fleming-Harrington, and Kaplan-Meier Methods" of the PROC LIFETEST documentation.
Note (in the procedure output "Quartile Estimates") that the upper confidence limit is not included in the interval, which can be easily overlooked when only the ODS output dataset is used.
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