<P> The denominator equals mean proportional species abundance in the dataset as calculated with the weighted generalized mean with exponent q - 1 . In the equation, S is the total number of species (species richness) in the dataset, and the proportional abundance of the ith species is p i (\ displaystyle p_ (i)). The proportional abundances themselves are used as weights . The equation is often written in the equivalent form: </P> <Dl> <Dd> q D = (∑ i = 1 S p i q) 1 / (1 − q) (\ displaystyle () ^ (q) \! D = \ left ((\ sum _ (i = 1) ^ (S) p_ (i) ^ (q)) \ right) ^ (1 / (1 - q))) </Dd> </Dl> <Dd> q D = (∑ i = 1 S p i q) 1 / (1 − q) (\ displaystyle () ^ (q) \! D = \ left ((\ sum _ (i = 1) ^ (S) p_ (i) ^ (q)) \ right) ^ (1 / (1 - q))) </Dd> <P> The value of q defines which kind of mean is used . q = 0 corresponds to the weighted harmonic mean, which is 1 / S because the p i (\ displaystyle p_ (i)) values cancel out . q = 1 is undefined, except that the limit as q approaches 1 is well defined: </P>

Why is species diversity a better measure than species richness