How trustworthy are risk assessment results, and what can be done about the uncertainties they are plagued with?

The paper will first briefly review a standard procedure introduced for safety cases on products that must provide more or less a guarantee that the risk of use is below a certain value. Next will be the various approaches of how to deal with uncertainties in a quantitative risk assessment and the follow-on decision process. Because expert estimates are often in high need to obtain some solution, various ways of expert elicitation and its limitations are considered. Special attention will be paid to the highly uncertain aspect of human reliability influenced by organizational factors and conditions. Over the last few years several new developments have been made to achieve, to a certain extent, a hold on so-called deep uncertainty. The paper will be concluded with some practical recommendations of how to judge the validity of risk assessments and how to reduce bias in the decision-making process.