Elementary Statistics and Computer Application

Poisson distribution

• The Poisson distribution, named after Simeon Denis Poisson(1781-1840). Poisson distribution is a discrete distribution. It describes random events that occurs rarely over a unit of time or space. It differs from the binomial distribution in the sense that we count the number of success and number of failures, while in Poisson distribution, the average number of success in given unit of time or space.

Definition

• The probability that exactly x events will occur in a given time is as follows


• called as probability mass function of Poisson distribution.
• where λ is the average number of occurrences per unit of time
• λ = np