The precautionary principle: Scientific uncertainty and type I and type II errors

We provide examples of the extent and nature of environmental and human health problems and show why in the United States prevailing scientific and legal burden of proof requirements usually cannot be met because of the pervasiveness of scientific uncertainty. We also provide examples of how may assumptions, judgments, evaluations, and inferences in scientific methods are value-laden and that when this is not recognized results of studies will appear to be more factual and value-neutral than warranted. Further, we show that there is a "tension" between the use of the 95 percent confidence rule as a normative basis to reduce speculation in scientific knowledge and other public policy and moral concerns embodied by the adoption of a precautionary principle. Finally, although there is no precise agreement regarding what a precautionary principle might entail, we make several recommendations regarding the placement of the burden of proof and the standard of proof that ought to be required in environmental and human health matters.