Many of us will have considered how people show higher sensitivity to dread risks, rare events that kill many people at once, compared with continuous risks, relatively frequent events that kill many people over a longer period of time. A current example would be the current concern over aeroplane accidents and oil train accidents on one hand compared to road accidents, which in a year kill many more people in North America, on the other.

Researchers at the Center for Adaptive Behavior and Cognition and the Harding Center for Risk Literacy at the Max Planck Institute for Human Development in Berlin, Germany,  have been studying this situation.

The researchers state that the different reaction to dread risks is often considered a bias: If the continuous risk causes the same number of fatalities, it should not be perceived as less dreadful. Their research tests the hypothesis that a dread risk may have a stronger negative impact on the cumulative population size over time in comparison with a continuous risk causing the same number of fatalities. This difference should be particularly strong when the risky event affects children and young adults who would have produced future offspring if they had survived longer.

Results show that dread risks affect the population more severely over time than continuous risks that cause the same number of fatalities, suggesting that fearing a dread risk more than a continuous risk is, on an evolutionary scale of time, an ecologically rational strategy.

This type of research should be of considerable value to those who communicate with the public about risks, accidents, and disasters. It is likely not acceptable, for entrenched anthropological reasons, to try to persuade people that plane crashes or train wrecks that only kill a few are not major disasters compared to the number of people dying on the roads or of serious diseases. Climate change, even though a potential global disaster for the human population, is a slowly evolving problem with little obvious impact on the size of the human population. That may explain why it is so difficult to get people engaged. The parable of the frog in the slowly warming pot of water may be as true for humans as it is for frogs.

The research,  Bodemer N, Ruggeri A, Galesic M (2013) When Dread Risks Are More Dreadful than Continuous Risks: Comparing Cumulative Population Losses over Time, is open source and available at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0066544