Analyse and interpret data associated with specific risk factors and the incidence of disease • recognise correlations and causal relationships.

The graph below compares the incidence (number of cases) of lung cancer to the risk factor of smoking.

cancerresearchuk

The age at which smoking was stopped has a direct correlation to the incidence.

This would appear to show that smoking causes cancer; but there could be other factors linking the two data which are actually the cause. To understand this imagine that people smoke because they are stressed and that stress is the cause of cancer- this would mean that as stress went up so did smoking and cancer (so there was a correlation), but that smoking was not the cause of cancer.

A casual relationship is the term for a direct link that shows one thing has caused another. In this case scientists analysed the affect of tar on cells and found that it altered the DNA causing cancerous mutations: they found a casual relationship between smoking and cancer.