I am beginner of survival analysis, so I am confused about some basic ideas in this area.
I think the basic assumption in survival analysis is that time of event for a subject can be estimated given all relevant time-invariable attributes of subjects. Therefore, ideally, if we can regress over the failure time correctly, we can then predict the expected failure time of subjects.
Since regression is hard, researchers transformed it to ranking problem. That is, they want to rank subjects according to their failure time. Furthermore, the performance of ranking is measured by concordance index (c-index).
My question is, "Even with a perfect ranking list (larger score for longer survival time), how can we determine the failure risk of each subject at time T?" @mbq, @ocram :)