# Logarithmic distribution

Parameters Probability mass functionThe function is only defined at integer values. The connecting lines are merely guides for the eye. Cumulative distribution function

In probability and statistics, the logarithmic distribution (also known as the logarithmic series distribution or the log-series distribution) is a discrete probability distribution derived from the Maclaurin series expansion

From this we obtain the identity

This leads directly to the probability mass function of a Log(p)-distributed random variable:

for k  1, and where 0 < p < 1. Because of the identity above, the distribution is properly normalized.

where B is the incomplete beta function.

A Poisson compounded with Log(p)-distributed random variables has a negative binomial distribution. In other words, if N is a random variable with a Poisson distribution, and Xi, i = 1, 2, 3, ... is an infinite sequence of independent identically distributed random variables each having a Log(p) distribution, then

has a negative binomial distribution. In this way, the negative binomial distribution is seen to be a compound Poisson distribution.

R. A. Fisher described the logarithmic distribution in a paper that used it to model relative species abundance.[1]

The probability mass function ƒ of this distribution satisfies the recurrence relation