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Statistical tests and power analysis for three in‐vivo bioassays to determine the quality of marine sediments
Author(s) -
van der Hoeven Nelly,
Kater Belinda J.,
Pieters Jan F.
Publication year - 2002
Publication title -
environmetrics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.68
H-Index - 58
eISSN - 1099-095X
pISSN - 1180-4009
DOI - 10.1002/env.517
Subject(s) - bioassay , toxicology , biology , sediment , mortality rate , statistics , zoology , mathematics , medicine , ecology , paleontology
Statistical tests are recommended for three marine sediment in‐vivo bioassays. In two bioassays ( Corophium volutator and Echinocardium cordatum ), the mortality in the sediment is compared with that in a control. An unconditional 2 × 2 test is recommended. For one bioassay (Rotoxkit M TM with Brachionus plicatilis ), mortality in a dilution series of pore water is compared with the mortality in a control. The Williams test for trends is recommended. For each of these tests the power to assess an effect has been calculated. The number of replicates recommended in the standardized test protocol only allows large effects to be observed in almost all (95 per cent) of the experiments. Given the control mortality rates estimated from a large set of controls, a power of 95 per cent will only be reached if the mortality rate in the tested sediment is over 30 per cent for C. volutator and almost 60 per cent for E. cordatum . To reach this power for bioassays with B. plicatilis , where five concentrations are compared with a control, the mortality rate in the lowest effect concentration should be about 35 per cent. As an alternative to no effect testing, it is suggested that whether the effect of a treatment remains below some chosen minimal relevant effect (MRE) should be tested. Given an MRE at a fixed mortality rate of 25 per cent and α = 0.05, at least 55 individuals are necessary to be reasonably sure (95 per cent) that a mortality of 10 per cent will not be declared toxic incorrectly. The tests for mortality are based on the assumption that the survival probabilities of individuals within a test vessel are independent. We have described a method to test this assumption and applied it to the data on C. volutator . Copyright © 2002 John Wiley & Sons, Ltd.