POWER, SAMPLE-SIZE AND TAXONOMIC SUFFICIENCY FOR MEASURES OF IMPACT IN AQUATIC SYSTEMS

As part of a larger program to examine the relationships between labor atory and ambient toxicity, data from a series of 28 marine microcosm experiments, which included both laboratory and held studies, were rea nalyzed. The statistical methods applied to the data include log-linea r regression models (general and robust) for richness and taxa count d ata (kingdom, phylum, class, order, family, genus, and species) and Ga ussian linear models (general and robust) for community metrics divers ity and evenness (Shannon-Weiner's, Simpson's, and Brillouin's) and si milarity (Bray-Curtis). In addition, taxonomic sufficiency was determi ned for each of the metrics examined. For each of the analyses perform ed, both the statistical power of the analysis and the sample sizes re quired to achieve a desired level of power were determined. New method s are presented to deal with zero count data. Suggestions on how the p ower of microcosm tests used in toxicity testing can be increased are provided. The statistical programs developed for the analyses applied to the data analyzed were done in S-PLUS. The programs and directions for their application have been placed on an anonymous FTP site at the University of North Texas.