# skbio.diversity.alpha.chao1¶

skbio.diversity.alpha.chao1(counts, bias_corrected=True)[source]

Calculate chao1 richness estimator.

State: Experimental as of 0.4.0.

Uses the bias-corrected version unless bias_corrected is False and there are both singletons and doubletons.

Parameters
• counts (1-D array_like, int) – Vector of counts.

• bias_corrected (bool, optional) – Indicates whether or not to use the bias-corrected version of the equation. If False and there are both singletons and doubletons, the uncorrected version will be used. The biased-corrected version will be used otherwise.

Returns

Computed chao1 richness estimator.

Return type

double

Notes

The uncorrected version is based on Equation 6 in 1:

$chao1=S_{obs}+\frac{F_1^2}{2F_2}$

where $$F_1$$ and $$F_2$$ are the count of singletons and doubletons, respectively.

The bias-corrected version is defined as

$chao1=S_{obs}+\frac{F_1(F_1-1)}{2(F_2+1)}$

References

1

Chao, A. 1984. Non-parametric estimation of the number of classes in a population. Scandinavian Journal of Statistics 11, 265-270.