Shannon-Wiener index

% also incorrectly known as Shannon-Weaver,is one of
% several diversity indices used to measure versity
% in categorical data. It is simply the Information
% entropy of the distribution, treating species as
% symbols and their relative population sizes as the
% probability.
% The advantage of this index is that it takes into
% account the number of species and the evenness of
% the species. The index is increased either by
% having additional unique species, or by having a
% greater species evenness.
% The value of the Shannon-Wiener Index usually lies
% between 1.5 and 3.5 for ecological data and rarely
% exceeds 4.0. According to Southwood and Henderson
% (2000), it is an insensitive measure of the character
% of the S:N relationship and is dominated by the
% abundant species.