Strong's Dominance Index

Strong's dominance index, Dw (Strong, 2002), is calculated using:

where

bi is the sequential cumulative totaling of the ith species abundance values ranked from largest to smallest;

Q is the total number of individuals in the sample;

R is the number of species in the sample

and

maxi is the largest calculated ith values

The meaning of the equation can be seen by studying the following figure reproduced from Strong (2002). The upper curve represents the species accumulation curve for the sample and the straight line a model in which each species has the same abundance.

To compare two indices see Testing for significant differences between indices.