You are in the supermarket and you buy a huge cream cake. You are also on a diet. Does this mean you intend to break your dieting?

There are times when the things we want to observe and measure are difficult to get a precise angle on. From the underlying motivations of voters in the Brexit referendum to what expressed religious beliefs in the census say about Britishness, one measure is often substituted for another when we are trying to make sense of the world. We call these proxy measures.

So what is a proxy? And what does and doesn’t it tell us?