The Simpson s-index considers the fractions with which a given protein was assigned to a functional class. This diversity index measures the probability of how closely related two proteins are and if they are of the same type aka, are responsible for the same functions. The index is defined as: s=∑Ni=1p2i where pi is the fraction of a given protein with a chosen functional class. If the functional class dominates that protein then the pi value will be closer to 1 and therefore we can conclude that if a unknown protein has a Simpson index close to 1, then the functional properties for that protein was accurately chosen.

Simplified Equation of Simpson's Index. R defines the richness of the dataset, aka the variety of the different functional classes within the set.