Is There a Role for Qualitative Risk Assessment?

Classically, risk is characterised by a point value probability indicating the likelihood of occur­ rence of an adverse effect. However, there are domains where the attainability of objective numerical risk characterisations is increasingly being questioned. This paper reviews the argu­ ments in favour of extending classical techniques of risk assessment to incorporate meaningful qualitative and weak quantitative risk characteri­ sations. A technique in which linguistic uncer­ tainty terms are defined in terms of patterns of argument is then proposed. The technique is dem­ onstrated using a prototype computer-based sys­ tem for predicting the carcinogenic risk due to novel chemical compounds.