Arguments for qualitative risk assessment: The StAR risk adviser

Calculating risk is relatively straightforward when there is reliable statistical evidence on which to base a judgment . However, novel technologies are often characterised by a lack of such historical data, which creates a problem for risk assessment. In fact, numerical risk assessment can be positively misleading in such situations. We describe a decision support system -- StAR -- that gives quantitative assessments where appropriate, but which is also able to provide qualitative risk assessments based on arguments for and against the presence of risk. The user is presented with a summary statement of risk, together with the arguments that underlie this assessment. Furthermore, the user is able to search beyond these top-level arguments in order to discover more about the available evidence. Here we suggest that this approach is well-suited to the way in which people naturally make decisions, and we show how the StAR approach has been implemented in the domain of toxicological risk assessment.