Spain’s Prime Minister declared a three period of mourning to mark the Madrid plane crash of 20 August. This reaction to the crash highlights yet again the intractable problem of finding a metric that everyone can agree upon for measuring risk.
The crash was what is sometimes referred to as a low-probability high-impact event. High impact is a malleable term. Compared to the Boxing Day tsunami or the Szechuan earthquake, the Madrid crash was a low-impact event. But compared to a road accident in which only a few people are killed, it qualifies as a high-impact event.
How should impact be measured? The number of fatalities caused by an event is a commonly used metric sometimes converted into cash. In Britain the last time I looked a life was deemed by the Department for Transport to be worth £1.5 million. But the number is indexed for inflation so may now be higher. The Madrid crash killed 153 people a loss, assuming a life is worth £1.5 million, of £229.5 million had it occurred in Britain. In Spain 153 people die in road accidents every 12 days events also worth £229.5 million.
The probability of an air accident causing a loss of £229.5 million is vastly less than the probability that in the next 12 days in Spain road accidents will cause a similar loss. Yet the first loss merits three days national mourning. The second losses merit a few column inches. In terms of mangled flesh and grieving family and friends the two losses are equivalent. In terms of media impact and popular reaction the numbers appear irrelevant. What kills you matters.