I think the Precautionary Principle" is a bogus way of thinking about risk. Eg, reopening schools. The precautionary principle must work in both directions – we (a) mustn& #39;t risk another outbreak and (b) mustn& #39;t risk children missing more schooling. It& #39;s a useless guide to action.

Instead, I like what& #39;s called the "error cost" approach: ask what path is likely to be worse if we& #39;re wrong, and weigh your decisions that way. What& #39;s the likely cost if, eg, it turns out kids do spread Covid and we send them to school? What if they don& #39;t and we keep them home?

A key element of this is reversability. If one option turns out to be a mistake, how easily can we change course? Another is identifiability: How easily can we tell that we& #39;ve made a mistake?

This is a useful way of thinking about some forms of regulation, too. Sometimes a regulation against some kind of activity wipes it out, so we can& #39;t learn in future if we were wrong about it, whereas allowing it allows us to learn more – and prohibit later, if necessary.