# Censoring and events in survival data

Source: https://onco.cc/terms/censoring-and-events/  
OnCo record `censoring-and-events` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A patient is censored when the study ends or they leave before the event (death or progression) happens, so we only know they survived at least that long.

## Summary

Censoring, in Wikipedia's definition, is when the value of an observation is only partly known; in survival analysis a right-censored patient has not had the event by the last follow-up. Survival methods (Kaplan-Meier, Cox regression, the concordance index) use censored patients up to their last known time. The number of events, not the number of patients, sets the statistical power of a survival model, which is why a cohort of two thousand with a hundred deaths is a small study.

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: right-censored; censored patients; censored observations; event count; number of events; events observed
- Tags: cansim-terms

## 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/censoring-events.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Censoring_(statistics)
- Wikipedia: https://en.wikipedia.org/wiki/Censoring_(statistics)

## Connected records

- terms: [C-index (concordance index), Harrell's and Uno's](https://onco.cc/terms/concordance-index/), [Cancer AI vocabulary (CanSim terms map)](https://onco.cc/terms/cancer-ai-vocabulary/), [Hazard ratio (HR)](https://onco.cc/terms/hazard-ratio/), [Kaplan-Meier curve, censoring and proportional hazards](https://onco.cc/terms/kaplan-meier-curve/), [Survival outcomes as time plus event (OS, PFS)](https://onco.cc/terms/os-pfs-time-event/), [Univariate Cox scores and time-dependent metrics](https://onco.cc/terms/time-dependent-auc/)

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JSON: https://onco.cc/api/v1/entities/censoring-and-events.json