None of these four statements seems like a particularly grand ambition. But there is, nevertheless, a problem. Unfortunately, some kinds of fairness are mathematically incompatible with others. Let me explain. Imagine stopping people in the street and using an algorithm to predict whether each person will go on to commit a homicide. Now, since the vast majority of murders are committed by men (in fact, worldwide, 96 per cent of murderers are male)37, if the murderer-finding algorithm is to make accurate predictions, it will necessarily identify more men than women as high risk.
