Indicators of uncertainty in chemical risk assessments.

For most of the chemical substances that are subject to regulatory and industrial decision making, important toxicological data are missing. The available dataset is often difficult to interpret, and the differences between alternative, scientifically reasonable interpretations may have major impact on decision making. Since such uncertainties are an important factor in decision making it is essential that they be reported in a transparent and understandable way. In order to clarify how toxicologists report uncertainties, 30 risk assessments for one and the same substance (trichloroethylene) from the years 1973-2001 were searched for phrases indicating uncertainty. These phrases can be divided between four categories: contentual, epistemic, conditionalising, and inferential uncertainty indicators. A typology of uncertainty indicators, based on these categories, is proposed. It is concluded that the use of uncertainty indicators in these texts is not transparent and that the development of standardised uncertainty indicators should significantly improve communications both within the scientific community and between scientists and policymakers.