## Quick Reference

A measure, h(*t*), of the chance that a component, still working at age *t*, is about to fail. Formally, it is defined by The hazard rate is related to the probability density function, f, and the survivor function,S, by the equation

f(*t*)= h (*t*) S(*t*).

For many situations the graph of a hazard rate is a bathtub curve (see diagram *opposite*): initially the rate is high as the component beds in, there is then a constant hazard rate, and finally the component starts to wear out.

**Hazard rate.** The typical bathtub curve that results from a plot of the hazard rate against time. A high initial rate falls to a ‘normal level’ and then slowly increases as ageing sets in.

**From:**
hazard rate
in
A Dictionary of Statistics »

*Subjects:*
Probability and Statistics.

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