At your own risk

Is it more dangerous to light a cigarette or to travel through Europe by car?

As all daily activities pose risks, such questions are frequently in everyone’s mind. But how do we calculate them? In most cases we rely on usual habits or on what media tell us about for example plane accidents or about the impact of smoking on our health. In recent times, however, mathematicians and statisticians have been trying to develop a “riskmeter”, a risk scale that could help us to assess risks with sufficient accuracy, like the Richter scale does for earthquakes.

«A riskmeter like that could be very useful in providing a tool that would allow comparisons among important risks caused by various hazards, whether these hazards are caused by voluntary activities, such as smoking or hang-gliding, or connected to risks in which we incur when we dedicate ourselves to voluntary activities that are not strictly necessary like eating meat or travelling by car» explains Brian Everitt, Director of the Institute of Biostatistics at London King's College.

The American mathematician John Allen Paulos explained one of the best examples of riskmeters in his famous essay “Innumeracy”. The scientist presented a scale of risk based on a specific formula: if a person out of a number N of people dies, the associated risk index is determined by the base 10 logarithm of N (log₁₀(N)). Despite appearances, the calculation is very simple: in order to reach the risk index, you must find a number that once risen to the power of 10 corresponds to the total number of deaths. For example, if in Italy one death out of 8,000 per year comes from car accidents, the associated risk index with driving a car will be calculated identifying what number corresponds to 8,000 if risen to the power of 10: in this case it is about 3.90. In Paulos’s scale, a risk index of 0 corresponds to certain death; values ​​that are minor than 3 indicate hazardous activities and numbers greater than 6 suggest unsafe or worrying actions.

Here are some examples taken from the American mathematician’s essay: playing Russian roulette once a year (0.8), smoking ten cigarettes a day (2.3), being struck by lightning (6.3) and death caused by a bee sting (6.8). «Of course this proposal needs improvement before it can be widely accepted or it can show its practical potential. – concludes Everitt – For example death does not need to be the only concern, also falling sick or being injured are important consequences of the exposure to risks and it would be necessary to quantify them with a useful index».

In other words, the research on riskmeters is far from being over.