SIMILARITY MEASURE BIAS IN RIVER BENTHIC AUFWUCHS COMMUNITY ANALYSIS

An extensive assessment was made of nine common similarity measures on the basis of their discriminative ability and bias in weighting of di fferent types of variation in species abundance between samples, by us ing sets of river macroinvertebrate samples. Seven ag glomerative hier archical clustering methods were applied to these measures. Successful site discrimination is defined as grouping of all replicate samples f rom a particular site. Major differences existed in the discriminative ability between the similarity measures. The measures overweight some types of variation and underweight the others to varying extents, whi ch is closely related to their discriminative ability. A new dissimila rity-similarity measure was devised to respond to all types of variati on with minimum bias. This measure yielded a higher percentage of corr ect site discrimination than the others tested. Use of an extra data s et confirmed the superior performance of the new measure and also indi cated that it could discriminate between sites of different water qual ity.