An exponentially distributed random variable
is common in situations of exponential decay,
usually representing the amount of time taken for something to happen,
e.g. the decay of a uranium nucleus (see Poisson process).
It has positive support
and is described by the following probability density function and Cumulative distribution function
may be thought of as the frequency of the event:
the higher , the shorter the time before the event occurs.
In fact, the expected period is exactly what one might assume by this analogy.