*In Royal Society open science *

*η*of available unethical strategies is small, the probability

*p*

_{ U }of picking an unethical strategy can become large; indeed, unless returns are fat-tailed

*p*

_{ U }tends to unity as the strategy space becomes large. We define an unethical odds ratio,

*p*

_{ U }from

*η*, and we derive a simple formula for the limit of

*p*

_{ U }in finite cases and how to deal with infinite strategy spaces. We show how the principle can be used to help detect unethical strategies and to estimate

*η*. Finally we sketch some policy implications of this work.

*Beale Nicholas, Battey Heather, Davison Anthony C, MacKay Robert S*

*2020-Jul*

**AI ethics, artificial intelligence, economics, extreme value theory, financial regulation**