Fowlkes–Mallows index

The Fowlkes-Mallows index is a way of measuring how accurately two sets of data agree with each other. It can be used to compare things like survey results or predictions with actual results. To understand it, imagine that you have two groups of people, each with a list of different things they like. The Fowlkes-Mallows index measures how much the two groups have in common – the higher the number, the more they have in common.