Simpson's Diversity Index Calculator
Enter category counts to evaluate Simpson's index, diversity, and reciprocal index for ecological or categorical datasets.
Simpson's index (D)
0.3550
Diversity (1 − D)
0.6450
Reciprocal (1 / D)
2.8169
| Category | Count | Proportion |
|---|---|---|
| SpeciesA | 30 | 30.00% |
| SpeciesB | 45 | 45.00% |
| SpeciesC | 25 | 25.00% |
How to Use This Calculator
- List categories with their counts (e.g., species counts, demographic responses).
- Ensure counts are non-negative and represent the same dataset.
- Review Simpson's index (D), diversity (1 − D), and the reciprocal index.
- Use the results to compare diversity across sites, treatments, or time periods.
Formula
D = Σ pi², where pi = ni / N
Diversity = 1 − D
Reciprocal index = 1 / D
N = total count, ni = count in category i
Lower D values (higher 1 − D) indicate greater diversity. The reciprocal index increases with diversity and equals 1 when only one category is present.
Full Description
Simpson's diversity index emphasizes both richness and evenness by summing squared proportions. It is widely used in ecology, sociology, and market analysis where diversity within categories matters.
The calculator provides multiple variants (D, 1 − D, 1 / D) commonly referenced in literature, offering flexibility depending on reporting preferences.
Frequently Asked Questions
How does Simpson's index differ from Shannon entropy?
Simpson's index squares proportions, weighting dominant categories more heavily. Shannon entropy uses logarithms and is more sensitive to rare categories.
Can I include categories with zero counts?
Yes, but they do not affect the calculation. Only positive counts contribute to proportions.
What is a good diversity score?
There is no universal benchmark; compare indices across groups or time to assess relative diversity.
Do proportions need to sum to 1?
No. Provide counts and the calculator normalizes them internally.