Statistical significance of sediment toxicity test results: Threshold values derived by the detectable significance approach

A number of methods have been employed to determine the statistical signifi cance of sediment toxicity test results. To allow consistency among compari sons, regardless of among-replicate variability, a protocol-specific approa ch has been used that considers protocol performance over a large number of comparisons. Ninetieth-percentile minimum significant difference (MSD) val ues were calculated to determine a critical threshold for statistically sig nificant sample toxicity. Significant toxicity threshold values las a perce ntage of laboratory control values) are presented for six species and nine endpoints based on data from as many as 720 stations. These threshold value s are useful for interpreting sediment toxicity data from large studies and in eliminating cases where statistical significance is assigned in individ ual cases because among-replicate variability is small.