A popular view of scientists is that they deal with certainties, but they are (or should be) the first to admit the limitations in what they know. Yet can scientists admit uncertainty and still be trusted by politicians and the public? Or would the language of possibilities and probabilities merely shift attention to those with more strident, confident arguments?
Nobody is expected to predict the future exactly. So there is generally no problem in acknowledging the risk of everyday activities, and it is natural to use past experience to be open and precise about the uncertainties. Patients may, for example, be told that for every one million operations there are expected to be five deaths related to the anaesthetic — that’s an anaesthetic risk of five micromorts (a one-in-a-million chance of dying) per operation. This is roughly equivalent to the risk of riding 30 miles on a motorbike, driving 1,000 miles in a car, going on one scuba-dive, living four hours as a heroin user or serving four hours in the UK Army in Afghanistan.
In more complicated situations, scientists build mathematical models that are supposed to mimic what we understand about the world. Models are used for guiding action on swine flu, predicting climate change and assessing whether medical treatments should be provided by the NHS.
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