# Math Help - Computing expectation and variance

1. ## Computing expectation and variance

The probability generating function of a negative binomial distribution is equal to
[sp/(1-qs)]^r -> where q = p-1

How does one use this to compute the expectation and the variance of a negative binomial distribution?

2. Originally Posted by clockingly
The probability generating function of a negative binomial distribution is equal to
[sp/(1-qs)]^r -> where q = p-1

How does one use this to compute the expectation and the variance of a negative binomial distribution?
Look at your notes or text, they/it should tell you how to get the moments from the
generating function. Alternativly see this (see section 2) document.

RonL