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Survival function

 
Wikipedia: Survival function

The survival function, also known as a survivor function or reliability function, is a property of any random variable that maps a set of events, usually associated with mortality or failure of some system, onto time. It captures the probability that the system will survive beyond a specified time. The term reliability function is common in engineering while the term survival function is used in a broader range of applications, including human mortality.

Another name for the survival function is the complementary cumulative distribution function

Definition

Let T be a continuous random variable with cumulative distribution function F(t) on the interval [0,∞). Its survival-, or reliability-function is:

R(t) = P(\{T > t\}) = \int_t^{\infty} f(u)\,du = 1-F(t).

Properties

Every survival function R(t) is monotone decreasing, i.e. R(u) < R(t) for u > t

The time, t = 0, represents some origin, typically the beginning of a study or the start of operation of some system. R(0) is commonly unity but can be less to represent the probability that the system fails immediately upon operation.

See also



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Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Survival function" Read more