Concordance index
= Concordance index
{title2=$C$}
A survival <concordance index> measures agreement between predicted risk ordering and observed event ordering over comparable subject pairs, with half credit for prediction ties. A pair is ordinarily comparable when the earlier observed follow-up ends in an event. Censoring-adjusted versions can reduce dependence on follow-up patterns. Good discrimination does not imply good <survival prediction calibration> or correct proportional hazards.