What is epidemiology?

Epidemiology is not the study of skin.

That might seem a strange statement to make, but a decent proportion of the people I tell about what I do seem to think it is, so I thought I’d clear that up from the outset.

In short, it involves the study of patterns of health and disease in populations. Diseases have causes ranging from genetics to ageing, bacteria, viruses, environmental exposures and lifestyle habits. By looking carefully at which groups of people become ill and when,  it is possible to identify possible causes, even if the mechanism from cause to effect is not yet clear.

Maintaining good health may simply reflect an absence of risk factors, but may also indicate an environment that is conducive to counteracting the effects of potentially harmful exposures (e.g. urban planning which is pedestrian friendly can counter-balance the effects of an increasing number of sedentary jobs). In this way, epidemiology can be viewed as the scientific basis of public health interventions – it provides the data to help plan ways to prevent disease and improve health.

Epidemiology has its limitations – good conclusions cannot usually be reached without large numbers of people to study. Correlations between risk factors and diseases don’t necessarily mean that one has caused the other. And even when conclusions are sound, there is a limit to how much we can say about the risk for an individual person – hence the defiant smoker in his 80s does not disprove the link between smoking and premature mortality. But overall we can learn a lot about health and disease by looking at population trends.

It’s usually referred to as ‘epi’ by people in the field, and ‘epidemiholiday’ by medical students who see it as a bit of a doss because it might appear to involve numbers more than patients. I like to think they will come to their senses in good time and realise how interesting and useful it can be.

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