The invsimpson calculator is the inverse of the classical simpson diversity estimator.
This parameter is preferred to other measures of alpha-diversity because it is an indication of the richness in a community with uniform evenness that would have the same level of diversity. So while measures such as the shannon index are somewhat abstract, the inverse of the Simpson index has some biological interpretation. Other advantages of the Simpson-based metrics are that they do not tend to be as affected by sampling effort as the shannon index. This calculator can be used in the summary.single, collect.single, and rarefaction.single commands.