Simpson's Diversity Index
Calculate Simpson's Diversity Index (SDI) online free. Enter species population counts to compute Simpson's Index D, Gini-Simpson index 1-D, and reciprocal index 1/D with breakdown tables and charts.
About This Calculator
Simpson's Diversity Index Calculator helps ecologists, biologists, and environmental scientists measure biodiversity in any community. By entering species population counts, you get three key metrics: Simpson's Index (D), the Gini-Simpson diversity index (1 − D), and the reciprocal index (1/D). This free online tool also provides a detailed breakdown table showing each species' contribution and interactive bar and pie charts for visual analysis.
The calculation follows the standard Simpson's Diversity Index formula: D = Σ n(n − 1) / N(N − 1), where n is the count of individuals in each species and N is the total count. Simpson's Diversity Index is then computed as 1 − D, giving a value between 0 and 1 where higher values indicate greater biodiversity. The reciprocal index 1/D represents the effective number of species in the community.
This index is widely used in ecology for comparing biodiversity across habitats, in conservation biology for assessing ecosystem health, and increasingly in social sciences for measuring diversity in organizations and communities.
Frequently Asked Questions
What is Simpson's Diversity Index?
Simpson's Diversity Index (1 − D) measures the probability that two randomly selected individuals from a community belong to different species. It ranges from 0 (no diversity, single species) to 1 (infinite diversity). It is also known as the Gini-Simpson index.
How do you calculate Simpson's Diversity Index?
Simpson's Diversity Index is calculated as 1 − D, where D = Σ n(n − 1) / N(N − 1). Here n is the number of individuals of a particular species, and N is the total number of individuals across all species. First compute D, then subtract it from 1 to get the diversity index.
What does a high Simpson's Diversity Index mean?
A high Simpson's Diversity Index (close to 1) indicates a community with high biodiversity — many different species with relatively even population sizes. Low diversity (near 0) means the community is dominated by one or a few species.
What is the difference between Simpson's Index D and Simpson's Diversity Index 1-D?
Simpson's Index D measures the probability that two randomly selected individuals belong to the same species — higher D means lower diversity. Simpson's Diversity Index 1 − D (Gini-Simpson index) reverses this so higher values mean greater diversity. The reciprocal index 1/D is also commonly used.
What is the Simpson's Reciprocal Index?
The Simpson's Reciprocal Index is 1/D, where D is Simpson's Index. It represents the effective number of species in the community. For example, if 1/D = 5, the community has the same diversity as a perfectly even community of 5 species.
Can Simpson's Diversity Index be used outside ecology?
Yes. Simpson's Diversity Index is widely used beyond ecology — in economics for measuring market concentration, in sociology for income or ethnic diversity, in business for workforce diversity analysis, and in linguistics for vocabulary richness.
What species population values should I enter?
Enter comma-separated counts representing the number of individuals observed for each species in your community. For example, '300, 335, 365' represents three species with those population counts. You can enter any number of species.
What is the range of Simpson's Diversity Index?
Simpson's Diversity Index (1 − D) ranges from 0 to 1. A value of 0 means the community contains only one species. A value approaching 1 means the community has many species with even distributions, approaching maximum diversity.