The Poisson distribution (the term first used by

f(x) = (lx *

for x = 0,1,2,...; 0 < l

where

l |
(lambda) is the expected value of x (the mean) |

e |
is the base of the natural logarithm, sometimes called Euler's e (2.71...) |

For a complete listing of all distribution functions, see Distributions and Their Functions.