The theory of possibility and fuzzy sets: New ideas for risk analysis and decision-making

The thesis presents three new methods of risk analysis and decision making. The methods are based on the theory of fuzzy sets which are an extension of set theory. They are also using the theory of possibility which, in turn, is based on the theory of fuzzy sets. The theory of possibility can be regarded as an alternative to probability theory, but possibility theory is adapted to humanistic systems with the inherent subjective and limited information content. The methods which have been developed are: Indication of risk, based on fault tree analysis, intended to give an indication of the risks in a system, to identify weak links, and to optimise the checking events applied; Ranking of risks, an approximate method with the objective comparing different alternatives and to identify risk factors for these; and Merging of subjective opinions, a method to be used in decision theory for merging linguistic statements given by different experts.

The thesis also presents a review of traditional ideas and methods being used in risk analysis, followed by a more penetrating analysis of the special needs of the construction industry. This forms the basis for the proposed methods.