Recent estimations of NOEC (no observed effect concentration) values for communities use single species effect data to predict the concentration at which not more than some particular acceptable percentage of the species in a community will be affected. This method has a number of difficulties, not the least of which is obtaining effects data for enough of the right species to accurately represent the whole community. Typically one has to make do with existing data sets in which the choice of species tested has been made for convenience rather than representativeness. Usually the raw data alone are not sufficient to make reasonable estimates. Statistical methods have been proposed which deal with this problem by assigning a specific distribution to the data. But assumption of a specific distribution may not be valid. We present an alternative method and an associated computer program which use resampling (bootstrap) methods to estimate the NOEC without assuming a specific distribution. This method has the advantage that no underlying distribution is assumed. Simulated and published data sets were used to compare this approach with published methods. The use of this technique to assess representativeness was also demonstrated
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