A graphical exploration of the relationship between parasite aggregation indices

TL;DR

This paper uses graphical methods to explore how different parasite aggregation indices relate to mean abundance and prevalence, revealing nonlinear relationships and questioning the adequacy of correlation as a summary measure.

Contribution

It provides a visual and analytical comparison of various parasite aggregation indices assuming negative binomial distributions, clarifying their interrelationships.

Findings

Relationships between indices are nonlinear

Correlations are insufficient to summarize these relationships

Contour plots effectively illustrate index relationships

Abstract

The level of aggregation in parasite populations is frequently incorporated into ecological studies. It is measured in various ways including variance-to-mean ratio, mean crowding, the $k$ parameter of the negative binomial distribution and indices based on the Lorenz curve such as the Gini index (Poulin's D) and the Hoover index. Assuming the frequency distributions follow a negative binomial, we use contour plots to clarify the relationships between aggregation indices, mean abundance and prevalence. The contour plots highlight the nonlinear nature of the relationships between these measures and suggest that correlations are not a suitable summary of these relationships.