The Precautionary Principle and Risk


The precautionary principle is that:

When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically.

It thus applies in situations of uncertainty: better safe than sorry. It has been criticised for holding back innovation. But a ‘precautionary measure’ can be anything that mitigates the risk, not just failing to make the innovation. In particular if the potential ‘harm’ is very mild or easy to remediate, then there may be no need for costly ‘measures’.


There may be a cancer risk from mobile phones. The appropriate response is to advise restraint in the use of mobile phones, particularly by young people, and more research.

In the run-up to the financial crisis of 2007/8 there was an (indirect) threat to human health. An appropriate counter-measure might have been to encourage a broader base of economic research, including non-Bayesians.


Volokh sees the principle as directed against “politically disfavoured technologies” and hence potentially harmful. In particular Matt Ridley considers that the German e-coli outbreak of 2011 might have been prevented if the food had been irradiated, but irradiation had been regarded as leading to a possible threat, and hence under the precautionary principle had not been used. But the principle ought to be applied to all innovations, including large-scale organic farming, in which case irradiation might seem to be an appropriate precautionary measure. Given the fears about irradiation, it might have been used selectively – after test results or to quash an e-coli outbreak.  In any event, there should be a balance of threats and measures.


The precautionary principle seems reasonable, but needs to be applied evenly, not just to ‘Frankenstein technologies’. It could be improved by emphasing the need for the measures to be ‘proportional’ to the down-side risk.

Dave Marsay


About Dave Marsay
Mathematician with an interest in 'good' reasoning.

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