ABSTRACT
The risk assessment aims at understanding and characterizing risk, in order to support decision-making related to risk. Risk assessment is in many ways an established approach, with suitable methods and models for responding to such questions and issues, founded to a large extent on probabilistic and statistical thinking and tools; see, for example, T. Bedford and R. Cooke, D. Vose, T. Meyer and G. Reniers, T. Aven and Y. Y. Haimes. This chapter focuses on the reliability and validity concepts introduced. The decision-maker can be satisfied with a risk assessment expressing a low probability number for an extreme event, without giving weight to the knowledge supporting it or the process for deriving this number. The quality of K and this process are obviously essential elements of the assessment. Risk assessments, and particularly quantitative risk assessments, are largely based on models to represent systems and processes.
