Probability weighted indices for improved ecosystem report card scoring

Abstract

This paper outlines a new method for computing an ecosystem index using probability weighted moments (PWMs) in place of conventional moments. Conventional methods of index construction are based on a scaled measure of the discrepancy between the sample mean and a guideline or reference value and as such tend to reflect only gross movements in distributional location. PWMs on the other hand allow for a more targeted assessment through the incorporation of a weighting function specified by the analyst. We refer to the resulting index as a probability weighted index or PWI. Although all data are used in the computation of the PWI, they do not necessarily contribute equally to the final result a..