{"entity":{"id":"concordance-index","kind":"term","name":"C-index (concordance index), Harrell's and Uno's","aka":["C-index","concordance index","Harrell's C-index","Harrell's C","Uno's C-index","Uno's C","C-statistic","pooled C-index","stratified C-index","within-type C-index"],"tldr":"The C-index is the fraction of patient pairs in which the model ranked the patient who had the event sooner as higher risk; 0.5 is a coin toss and 1.0 is perfect ranking.","summary":"Harrell and colleagues introduced the concordance index as the probability that, for a random pair of patients, the one predicted to be at higher risk has the earlier event; Uno and colleagues gave a version that weights pairs by the inverse probability of censoring so that heavy censoring does not bias it upwards. A pooled pan-cancer C-index is inflated by tissue of origin (leukaemia patients die sooner than thyroid patients), so within-type or stratified C-indices are the honest measure. The C-index ranks; it says nothing about calibration.","asOf":"2026-09-24","links":[{"label":"Harrell et al., Evaluating the yield of medical tests (JAMA 1982)","url":"https://doi.org/10.1001/jama.1982.03320430047030"},{"label":"Uno et al., On the C-statistics for evaluating overall adequacy of risk prediction procedures with censored survival data (Statistics in Medicine 2011)","url":"https://doi.org/10.1002/sim.4154"}],"tags":["cansim-terms"],"related":["cancer-ai-vocabulary"],"cancers":[],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["censoring-and-events","calibration","time-dependent-auc","hazard-ratio","organ-of-origin-signal"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":["Listed in the CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme; CanSim page path /terms/c-index."],"provenance":{"editedBy":"OnCo CanSim terms wave (Wikipedia summaries, standards and project pages, GDC and FDA pages, Europe PMC)","editedOn":"2026-09-24","note":"CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme"},"category":"Methods and models"},"route":"/terms/concordance-index/","neighbours":{"term":[{"id":"calibration","kind":"term","name":"Calibration: reliability diagrams and the Brier score","route":"/terms/calibration/"},{"id":"cancer-ai-vocabulary","kind":"term","name":"Cancer AI vocabulary (CanSim terms map)","route":"/terms/cancer-ai-vocabulary/"},{"id":"censoring-and-events","kind":"term","name":"Censoring and events in survival data","route":"/terms/censoring-and-events/"},{"id":"hazard-ratio","kind":"term","name":"Hazard ratio (HR)","route":"/terms/hazard-ratio/"},{"id":"prognosis-risk-percentile","kind":"term","name":"Risk score and risk percentile","route":"/terms/prognosis-risk-percentile/"},{"id":"roc-auc","kind":"term","name":"ROC-AUC, PR-AUC and time-dependent AUC","route":"/terms/roc-auc/"},{"id":"organ-of-origin-signal","kind":"term","name":"Tissue-of-origin signal in tumour data","route":"/terms/organ-of-origin-signal/"},{"id":"time-dependent-auc","kind":"term","name":"Univariate Cox scores and time-dependent metrics","route":"/terms/time-dependent-auc/"}]}}