Simpson's Index Calculator

How to use this calculator

Simpson's Reciprocal Index tells us how diverse an area is. It looks at two things: how many different species live there, and how evenly the organisms are spread among those species. A higher D means more diversity.

1. Find your data table from the simulation.

2. Type the number of each organism (n) into the "Present" and "Absent" columns. If a species wasn't found, leave it blank or type 0.

3. Watch the n(n−1) column fill in. For example, 4 mice gives 4 × 3 = 12. Compare these numbers to your worksheet to check your math.

4. Click Calculate Both Indexes to see the D value for each area.

5. Copy the totals and D values onto your worksheet, then compare them. Which area is more diverse? What role might the gopher tortoise play?

Why does evenness matter? Picture two areas, each with 20 organisms and 4 species. In one, there are 5 of each species. In the other, there are 17 of one species and 1 each of the other three. The first area is more diverse, even though both have the same number of species.