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Being an epidemiologist means always having to say you're sorry. Epidemiology has constantly been criticised for the problems of lack of randomisation of exposures, misclassification of exposures and outcomes, and inadequate control of confounding.1 Nevertheless, epidemiologists continue to make important scientific discoveries, ranging from Snow's work on cholera2 to the discovery of tobacco smoking3 and asbestos4 as major causes of lung cancer, through to more recent discoveries such as the link between human papillomavirus (HPV) and cervical cancer.5 All of these discoveries took decades to become accepted, but eventually successful public health interventions followed. We must be doing something right.
Of course, we can also get things wrong, and there are many examples of findings which hit the headlines but were not replicated when further studies were carried out.6 It is therefore not surprising that the public may be sceptical of epidemiological findings.6 Perhaps the problem is not that epidemiology is more prone to error than other sciences (basic researchers, for example geneticists, probably get things wrong at least as often, and often hype up their findings even more than we do), but that our mistakes may be more likely to be highlighted by the media. Examples include studies of β carotene and cardiovascular disease, hormone replacement therapy, vitamin E and vitamin C intake in relation to cardiovascular disease, and fibre intake in relation to colon cancer.7
However, these examples of ‘epidemiological failures’ primarily involve studies of lifestyle factors (particularly diet). These are notoriously difficult to investigate, since the exposed group (eg, those with high β carotene levels in their diets) will often be markedly different from the non-exposed group as regards other lifestyle factors. Ironically, some areas of epidemiological research are less prone to error, but these are often areas in …