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Keywords:

  • water quality;
  • trend detection;
  • errors;
  • tolerance requirements

ABSTRACT: In designing a water quality sampling program, the detection threshold (equivalent to “effect size” in a power analysis) can be calculated as a function of the Type I and II error risks, sampling frequency and duration, and (if appropriate) autocorrelation. Then the impact of sampling and analytical errors on the trend that can be detected within that threshold should be considered. A procedure for doing so is described, enabling a priori prescription to laboratory and field staff of the analytical tolerances expected of them in their work. It assumes that the trend (a linear or step change) can be described by a parametric model.