E.g. 24,000 people died in 2005. The population was 72,200,000. What is the average risk in:

  • Percentage: 24,000 / 72,200,000 = 0.033%
  • Fraction: 72,200,000 / 24,000 = 1 in 3008 people

These averages make the assumption that everyone has the same chance of the outcome = WRONG.

Perception of risk

People’s behaviour is affected by the perception of risk.

They overestimate the risk of something happening if the risk is not under their control, unnatural, unfamiliar, dreaded, unfair or very small.

There is a tendency to underestimate the risk if it has an effect in the long-term future e.g. health risks associated with smoking.

When data is lacking to estimate the risk, the outcome is uncertain.

Correlation and cause

Two factors are positively correlated if an increase in one is accompanied by an increase in the other

A positive correlation does not necessarily mean that the two are causally linked.

Factors that contribute to health risks include:

  • heredity
  • physical environment
  • social environment
  • lifestyle and behaviour choices