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Keywords:

  • Ampelisca;
  • Amphipod;
  • t Test;
  • Statistical variance;
  • Test acceptability

Abstract

Current acceptability requirements for toxicity tests are often more restrictive than necessary. They focus primarily on response in a control and generally ignore what a test was “designed” to detect as a significant difference from that control. An approach is presented that takes into account the performance of an entire test and the magnitude of the deviation from the current acceptability requirements. The procedure is based on analyzing the past statistical performance of a test method (i.e., what kind of difference from the control was the test designed to detect). It takes into account traditional control acceptance criteria, but adds a requirement for selecting a difference from the control desired to be detected as statistically significant (a threshold value). Choice of statistical procedure is not relevant to the approach. The proposed method allows a sliding scale of acceptance. The greater the deviation of mean control response below current requirements, the less likely a test is to be accepted. An example is presented using data from a 10-d sediment test using the marine amphipod Ampelisca abdita. Use of the proposed acceptability criterion will reduce the frequency of required retesting without sacrificing defensibility of data. Using the old acceptability criterion, 19% of the samples in the amphipod data set would require retesting. The proposed criterion reduces the potential percentage of retests to 9%.