Most of us have broken a bit of our body at some point. But you did not go and count the number of people who broke their ankle playing your sport. You go and play without working out the likelihood of breaking your ankle. But if you have torn a hamstring, you may not risk playing on it - unless it is an important game.

Risk must be put into context. It does not occur as an entity in itself. It is part of a 'package' of attributes. This includes technology (e.g. nuclear power) or locale (e.g. earthquake zone) and way of life (e.g. bungy jumping). Risk may be calculated in mathematics, but it is still a lot of guesswork.

Which is the most dangerous sport?

This makes measurement of risk difficult. People perceive risks in ways that may have little bearing on the actual measured level of risk. It often depends where you stand.

Pesticide risks to health for people working in agriculture are measured less than the risk of musculo-skeletal disorders (MSD) from inappropriate machines, which 80% will suffer at some point. Pesticides pose wider risks to impacts on land, air, water and food, often many miles from their source.

People are generally more concerned about chemical pollution of rivers and the sea and disposal of toxic waste than about ozone layer depletion and drinking water quality. Women are usually more concerned than men and older people more than young.