Diversity Index - Gini-Simpson Index

Gini-Simpson Index

The original Simpson index λ equals the probability that two entities taken at random from the dataset of interest (with replacement) represent the same type. Its transformation 1 - λ therefore equals the probability that the two entities represent different types. This measure is also known in ecology as the probability of interspecific encounter (PIE) and the Gini-Simpson index. It can be expressed as a transformation of true diversity of order 2:

The Gibbs-Martin index of sociology, psychology and management studies, which is also known as the Blau index, is the same measure as the Gini-Simpson index.