Calculating the confidence interval for median survival.     

While Prism computes the confidence interval for the ratio of median survivals (when you compare two groups), it does not compute the 95% confidence interval for the median survival time itself.

There are multiple methods for computing a confidence interval of median survival:

• One method is in Collett starting at page 35 . 
• Brookmeer and Crowley , A confidence interval for the median survival time. Biometrics (1982) vol. 38 (1) pp. 29-41
• Barker reviews several methods and points out how different their results can be. The Mean, Median, and Confidence Intervals of the Kaplan-Meier Survival Estimate—Computations and Applications. The American Statistician (2009) vol. 63 (1) pp. 78-80

Given the fact that there are multiple methods with varying results (based, I think, on different assumptions), and none appear to be standard, we have not implemented any of these methods in Prism. Please let us know if you disagree with our decision, and explain what you would like Prism to do.