Harrell’s concordance index

Harrell’s concordance index, often called C-index, is a statistical measure used to evaluate the performance of risk prediction models, especially in survival analysis. It assesses how well the model correctly ranks individuals based on their predicted risk of an event occurring, such as death or disease progression. A C-index of 0.5 indicates no predictive ability (like random guessing), while a value of 1.0 means perfect prediction. Values closer to 1.0 suggest the model is effective at distinguishing between higher and lower risk individuals, making it a valuable tool in medical research and decision-making.