A novel approach to reducing uncertainty: The group Delphi

A variation on the conventional Delphi was used to assemble an informational summary of expert opinion regarding the risks involved with the application of sewage sludge to farmland. The aim was to reduce uncertainties surrounding the associated health and environmental risks so agreement among citizens, farmers, and regulators could be reached. An expert panel was assembled for one day to take part in a structured communication process modeled after the Delphi. A two-part questionnaire using Likert scaling and open questions was iterated among rotating subgroups to build consensus and define disagreement. Plenary discussions were held between iterations to foster peer review. There was consensus about the risks of heavy metals, pathogens and nutrients; but clear disagreement about the risks of organic toxins. Existing state regulations were deemed inadequate only for lead and some organic toxins. Expert quantitative ratings were found to differ radically for two hypothetical contexts: academic and public.