Abstract: Indices summarizing community structure are used to
evaluate fundamental community ecology, species interaction,
biogeographical factors, and environmental stress. Some of these
indices are insensitive to gross community changes induced by
contaminants of pollution. Diversity indices and similarity indices are
reviewed considering their ecological application, both theoretical
and practical. For some useful indices, empirical equations are given
to calculate the expected maximum value of the indices to which the
observed values can be related at any combination of sample sizes at
the experimental sites. This paper examines the effects of sample size
and diversity on the expected values of diversity indices and
similarity indices, using various formulae. It has been shown that all
indices are strongly affected by sample size and diversity. In some
indices, this influence is greater than the others and an attempt has
been made to deal with these influences.