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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.

Definition

Let X 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



 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Survival_function". A list of authors is available in Wikipedia.
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