The Poisson distribution is a discrete distribution, completely characterized by one parameter l:
(where k! = 1 x 2 x ... x k).
Both the mean and the variance of Poisson distribution are equal to l.
The Poisson distribution parameter l describes the number of random events per an interval in space (e.g. events per square mile) or time (e.g. events per hour). Common examples include website visitors per hour, cars arriving at a tool plaza per minute, or seed germinations per square meter
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