Shannon’s index conveniently combines
abundance and evenness parameters but
does not allow statistical comparison of the
richness of populations with different sample
sizes. “Rarefaction” was developed as a
means of statistically describing species
richness in a community. As applied in this
case, pathotype richness can be described
in a population in such a way as to permit
comparisons among different populations
(13,20). Using this technique, the expected
number of pathotypes, E(Sn), in a random
subsample from a population with an observed
pathotype abundance distribution
can be calculated as follows: