tify cause-and-effect relationships. Variations on this approach (often combined with statistical analysis) are used in product testing, including clinical trials for drugs and therapeutic devices. The scientific rationale for this method is that it establishes the cause or causes of a risk. Laboratory experiments can be used to establish a potential hazard (Hilbeck et al. 2000), and field experiments can be used to evaluate potential risks (e.g., Orr and Landis 1997). With field experiments, however, it is necessary to guard against false negatives (type II statistical errors), which would lead to concluding erroneously that there is no risk when, in fact, the experimental design is incapable of detecting any risk except a very large one (Marvier 2001).
Expert judgments. A group of experts use personal knowledge of a given system to estimate likely system performance under untested conditions. This is a widely used approach in risk analysis and has become the basis for risk analysis for some invasive species in the United States (Orr et al. 1993). The group is chosen to represent a range in necessary expertise with due consideration to potential conflicts of interest. The scientific rationale for this method is that the consensus of the group of experts represents a synthesis of the best-available scientific knowledge on the risk (Jasonoff 1986). The Environmental Protection Agency (EPA) uses this method frequently to aid in risk assessment of transgenic plants in its SAP (Scientific Advisory Panel) process, and the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service Biotechnology, Biologics, and Environmental Protection unit (USDA-APHIS-BBEP) has used it to evaluate the initial notification system for transgenic plants (USDA-APHIS 1993).
Expert regulatory judgment. Regulatory personnel use personal knowledge of a given system to estimate likely system performance under untested conditions. This is the most widely used approach in risk analysis. The scientific rationale for this method is that regulatory personnel have ready access to confidential business information and understand both current scientific knowledge and the process of risk analysis, so their judgments can be rendered with minimal delays and sufficient scientific accuracy. This is the method used by USDA-APHIS-BBEP to evaluate most of the complex, difficult-to-measure potential risks associated with transgenic plants.
The first three of these approaches are generally accepted as scientifically rigorous methods of analysis. Expert judgment, whether by external experts or by regulatory judgments are less rigorous, but often acceptable. A consensus of multiple external experts is likely to be more rigorous than the expert regulatory judgments because disagreements among external experts are likely to lead to more robust risk assessments (Jasanoff 1986).