When data shows over- or underdispersion with respect to this distribution, a modification named for Conway and Maxwell is used. The Robbins Lemma is 
When data shows over- or underdispersion with respect to this distribution, a modification named for Conway and Maxwell is used. The Robbins Lemma is used to relate expected values from this distribution. The difference between two variables that follow it is given by the Skellam distribution, and its nth moment is equal to the number of partitions of a set of size n. Used to model chemical DNA mutagenesis, calls to a call center, or horse-kicks in the Prussian army, it contains a single parameter lambda which is both its mean and variance. For 10 points, name this distribution used to model rare events, named for a Frenchman.
When data shows over- or underdispersion with respect to this distribution, a modification named for Conway and Maxwell is used.
{Poisson} distribution