See also
Alpha diversity
Alpha diversity metrics
Novel alpha diversity metrics
Log-normal abundance distribution
The singleton-free estimator (FE) (R.C. Edgar and H. Flyvbjerg, manuscript in preparation) estimates total richness using a non-parametric theory similar to Chao1, except that singletons are not considered. Let
N = number of observed OTUs,
nk = number of observed OTUs with abundance k.
Then FE is calculated as
FE = N - n1 + 2n23/9n32
+ 2n22/3n3.