Chao & Lee 1 
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This is also known as an ACE estimator of richness ( Abundancebased Coverage Estimator of species richness). The method was developed by Chao and Lee (1992)
It is assumed that
The sample coverage estimate based on abundance data is defined as:
where
Thus, this sample coverage estimate is the proportion of all individuals in rare species that are not singletons. Then the ACE estimator of species richness is
The estimate the coefficient of variation of the Fi's is
If Number of Random Selections (R) is set > 1 then the sequence samples are selected R times at random from the complete set of samples, and the mean estimate calculated. As this removes sample order effects it is generally to be recommended.
By looking at the progressive change in the estimates it is possible to assess if sufficient samples have been taken to stabilise the estimate.
A simple plot of the way the estimate changes with the number of samples used is shown by clicking on the Graph tab.
