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**Simpson’s Diversity Index** is a way to measure the diversity of species in a community.

Denoted as *D*, this index is calculated as:

*D* = Σn_{i}(n_{i}-1) / N(N-1)

where:

**n**The number of organisms that belong to species_{i}:*i***N:**The total number of organisms

The value for Simpson’s Diversity Index ranges between 0 and 1. The higher the value, the lower the diversity.

Since this interpretation is a bit counterintuitive, we often calculate **Simpson’s Index of Diversity** (sometimes called a Dominance Index), which is calculated as 1 – D. The higher the value for this index, the higher the diversity of species.

We can also calculate **Simpson’s Reciprocal Index**, which is calculated as 1/D. The lowest value for this index is 1 and the highest value is equal to the number of species.

For example, if there are 7 different species then the max value for this index would be 7. The higher the value for this index, the greater the diversity of the species.

The following step-by-step example shows how to calculate these various indices for a given community.

**Step 1: Collect the Data**

Suppose a biologist wants to measure the diversity of species in a local forest. She collects the following data:

**Step 2: Calculate N**

Next, she can calculate the total number of organisms.

There are **105** total organims.

**Step 3: Calculate n**_{i}(n_{i}-1)

_{i}(n

_{i}-1)

Next, she can calculate n_{i}(n_{i}-1). For example, the first species would be calculated as 40*(40-1) = 1,560. She can repeat this calculation for each species:

**Step 4: Calculate Simpson’s Diversity Index**

Lastly, we can use the following formula to calculate Simpson’s Index:

*D* = Σn_{i}(n_{i}-1) / N(N-1)

Using the values we found earlier, **Simpson’s Index** can be calculated as:

*D* = 2,668 / (105*(105-1)) = **0.244**.

We can also calculate **Simpson’s Index of Diversity** as 1 – *D* = 1 – 0.244 = **0.756**.

We can also calculate **Simpson’s Reciprocal Index** as 1 / *D* = 1 / .244 = **4.09**.

**Additional Resources**

Feel free to use this Simpson’s Diversity Index Calculator to automatically calculate Simpson’s Diversity Index for any dataset.