Lex parsimoniae e indici di qualita ecologica: il caso M-AMBI

M-AMBI is one of the most widely used benthic quality indices for coastal and transitional waters in Europe. It is based on macroinvertebrates and integrates the biotic index AMBI, Shannon diversity and species richness by means of factor analysis. We reproduced and analysed the algorithm using the open source R software. In this way we were able to demonstrate that factor analysis itself is a skeumorph, i.e. "a design feature that is no longer functional in itself but, was functional at an earlier time". Therefore, its omission does not appreciably change the results. Moreover, M-AMBI can be approximated by the simple mean of the normalised metrics, in this way removing the original dependence to the number of samples. Finally, we proposed a bivariate version, integrating a "sensitivity" and a "diversity" metric, still highly correlated with M-AMBI. The properties of these parsimonious versions of the algorithm include simplicity, transparency, robustness and ecological meaningfulness.