Vikas C. Raykar Harald Steck Balaji Krishnapuram Cary Dehing-Oberije Philippe Lambin On Ranking in Survival Analysis: Bounds on the Concordance Index. 2007 NIPS http://books.nips.cc/papers/files/nips20/NIPS2007_0535.pdf conf/nips/2007 db/conf/nips/nips2007.html#RaykarSKDL07