What is "censoring"

n. An act of censorship. vb. (present participle of censor English)

1. n. counterintelligence achieved by banning or deleting any information of value to the enemy [syn: censorship, security review]

2. deleting parts of publications or correspondence or theatrical performances [syn: censorship]

Censoring may refer to:

• Censoring (statistics)
• Censorship

In statistics, engineering, economics, and medical research, censoring is a condition in which the value of a measurement or observation is only partially known.

For example, suppose a study is conducted to measure the impact of a drug on mortality rate. In such a study, it may be known that an individual's age at death is at least 75 years (but may be more). Such a situation could occur if the individual withdrew from the study at age 75, or if the individual is currently alive at the age of 75.

Censoring also occurs when a value occurs outside the range of a measuring instrument. For example, a bathroom scale might only measure up to . If a individual is weighed using the scale, the observer would only know that the individual's weight is at least .

The problem of censored data, in which the observed value of some variable is partially known, is related to the problem of missing data, where the observed value of some variable is unknown.

Censoring should not be confused with the related idea truncation. With censoring, observations result either in knowing the exact value that applies, or in knowing that the value lies within an interval. With truncation, observations never result in values outside a given range: values in the population outside the range are never seen or never recorded if they are seen. Note that in statistics, truncation is not the same as rounding.

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.

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.