Simpson's Diversity Index Calculator
Calculate Simpson's diversity index from species abundance data. Enter the number of individuals for each species and get D, the diversity index (1-D), and the reciprocal index (1/D).
Simpson's diversity index measures the probability that two randomly selected individuals from a community belong to the same species. It accounts for both species richness and evenness.
The Formula: D = Σ [nᵢ(nᵢ - 1)] / [N(N - 1)]
Where nᵢ is the count of species i and N is the total number of individuals. This version uses the finite-sample correction (sampling without replacement).
Three Related Measures:
- Simpson's Index (D): Ranges from 0 to 1. Higher values mean lower diversity (dominated by one species).
- Simpson's Diversity Index (1 - D): Ranges from 0 to 1. Higher values mean higher diversity.
- Simpson's Reciprocal Index (1/D): Starts at 1 and increases with diversity. Maximum value equals the number of species (when all species have equal counts).
Example: A forest with 50 oaks, 30 maples, and 20 pines has N = 100. D = [50(49) + 30(29) + 20(19)] / [100(99)] = 3700/9900 = 0.374. The diversity index is 1 - 0.374 = 0.626, indicating moderate diversity.