Black Swans and Perfect Storms

Concerning news about a fire as consequence of shelling at Europe’s most powerful nuclear power plant… (1, 2).

Just three weeks ago, I summarised some articles about risk management of nuclear power plants and how the probability of a threat is calculated. Two of the human errors according to Paté-Cornell (2012) in risk assessment are that we often don’t consider two events, black swans and perfect storms. The perfect storm presents a situation where rare but known events randomly concurre, creating an extreme danger for us as we by judge such a coincidence as an extremely unlikely event (the Fukushima accident 2011 is such an example). This uncertainty is called aleatory uncertainty. Black swans, on the other hand, describe a situation where we do not even know about the existence of the event and even less about the distribution of the event parameters. It is the ultimate epistemic uncertainty (Paté-Cornell, 2012). By not considering these two possible events in risk analysis, the uncertainty in risk assessment rises. Meaning, we judge the likelihood of an event much rarer than it might actually be. As a consequence, we might be not prepared for such an event. The happenings in Ukraine show that things we judged as extremely unlikely, can happen.

How should we handle this uncertainty? What do you think?


Paté-Cornell, P. (2012). On “Black Swans” and “Perfect Storms”: Risk analysis and management when statistics are not enough. Risk Analysis: An International Journal, 32(11), 1823-1833.

(1) International Atom Energy Agency

(2) New York Times

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