Censoring (clinical trials)

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The term censoring is used in clinical trials to refer to mathematically removing a patient from the survival curve at the end of their follow-up time. Censoring a patient will reduce the sample size for analyzing after the time of the censorship. Reducing the sample size always reduces reliability, so the more patients are censored and the earlier they are censored the more unreliable the results are.[citation needed][dubious ]

Censoring is a form of missing data problem which is common in survival analysis. In statistics, engineering, economics, and medical research, censoring is a condition in which the value of a measurement or observation is only partially known.

Many clinical trials are designed with a minimum follow-up time. This means that the results aren't reported until that amount of the time after the last patient signed up for the trial. Often reports of the preliminary results don't include any minimum follow-up time and include the patients with very short follow-up time which definitely affects the reliability of the result.


  • AR Waladkhani. (2008). Conducting clinical trials. A theoretical and practical guide.

ISBN 978-3-940934-00-0