Setting the Framework for Risk Assessment - Blaise Pascal

Source: Wikipedia

Risk, according to Leibniz, is defined as the probability of loosing. Pascal was one of the first men who formulated a workable framework to assess and quantify natural risk. Based from his letter exchanges with Leibniz and Huygens, Pascal linked the numerical assessment of probability to the presupposition of the immutability of nature in order to forecast the occurrence of an unfortunate event. His ideas were published in 1662 in Logica sive Ars Cogitandi in the context of pondering the character of judgments about future events. He argued that:

...[people] consider only the greatness or importance of the benefit they desire or the disadvantage they fear, without considering in any way the likelihood or probability that this benefit or disadvantage will or will not come about.

Pascal argued that the reasonableness of courses of action should be pondered by weighing the supposed benefits of the (un)desired outcome by the frequency (likelihood) of the events that lead to those outcomes. The framework to measure this had, for Pascal, the same form as when one measures the stakes in a game of chance:

... in order to decide what we ought to do to obtain some good or avoid some harm, it is necessary to consider not only the good or harm in itself, but also the probability that it will or will not occur, and to view geometrically the proportion all these things have when taken together.

and then he clarifies these observations with an example: (Logica, 274-275)

...many people […] are excessively terrified when they hear thunder.... if it is only the danger of death that fills them with their extraordinary fear, it is easy to show that this is unreasonable. It would be an exaggeration to say that one in two million people is killed by a thunderstorm; there is scarcely any kind of violent death less common. Fear of harm ought to be proportional not merely to the gravity of the harm, but also the probability of the event, futurity so to speak, and since there is scarcely any kind of death more rare than death by thunderstorm, there is hardly any which ought to occasion less fear.

This account risk (fear of harm) connotes a spatiotemporal relation (futurity) which is measured by convolving the probability of concurrence of hazard (infrequent lightning), exposure (person), and the vulnerability (harm when hit by thunderstorm). Conceptually:

Risk ≡ p(Hazard ∩ Exposure)

in which p() is the probability of the conjunction (∩) between the hazard and the exposure. This notation amounts to a ‘latent event’ diagram that will be discussed in a future post.