ABSTRACT
A mathematical model of a risk should accurately match the behaviour of the risk. The set of behaviours that can be modelled needs to be sufficient to cover all possible risks. To model a risk requires an understanding of its behaviour and a Lego box of different mathematical constructions that can be assembled in appropriate ways to represent that behaviour. The risk modelling elements are called as primitives. The primitive is used in risk models where the risk is that there is an uncertainty in the quantity of something: materials, labour, services, anything. Risk modelling is essentially a pre-contract activity, that is to say, it takes place before major construction contracts have been awarded, and while funding is still being sought. The timescale calculation uses fixed durations for each component task. There is a close similarity between the spread duration and the fuzzy overlap in that both describe a period of time whose length is uncertain.
