Simpson's Diversity Index Calculator

Simpson's Diversity Index Calculator: Probability-Based Diversity Score

Simpson's Diversity Index answers a very concrete question: if you picked two individuals at random from a community, what's the probability they'd belong to different species? This calculator computes that probability directly from your species abundance counts.

The Formula

D = 1 − [Σ(n_i(n_i − 1))] / [N(N − 1)]

Worked Example

A community sample has 40, 30, 20, and 10 individuals across four species (100 total).

D = 1 − 2,900/9,900 = 0.7071

How to Use This Calculator

1. Enter the individual count for each species sampled (at least two species).
2. Click Calculate to get Simpson's Diversity Index.

Related Calculations

Compare against the Shannon Diversity Index Calculator, which weights rare species more heavily than Simpson's index does.