The healthy participant effect . . . and other stories

The healthy participant effectPeople who participate in epidemiological studies aren’t necessarily representative of the populations they come from. What’s more, in case-control studies different response rates in cases and controls can distort the findings. In a large study of breast cancer, with a participation rate of 43% for controls and 64% for cases, mortality among controls was only two thirds that of the reference population (Am J Epidemiol doi:10.1093/aje/kwae155). This may not have biased the findings in this particular investigation because, for causes of death other than breast cancer, mortality was similar in cases and controls. However, in many studies, adjusting for biases arising from the healthy participant effect is impossible.Air pollution and psoriasisPsoriasis is an inflammatory disease which, like many conditions of unknown aetiology, is usually ascribed to interactions between environmental and genetic factors. Data from nearly half a million participants in a UK longitudinal study who were free…
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