Economists have spent decades modelling expertise as a quantity. It behaves more like a weather system. The measure that matters is not what people say about expertise but what they do when nobody is scoring. It is tempting to call this irrational. It is more useful to ask what it is for. The point is not that people are foolish. The point is that expertise is expensive, and we economise on it like everything else.
Three kinds of mistake
Put a number on expertise and it becomes a target; put a target on it and the number stops meaning what it meant. The remedy is rarely exhortation. It is a change to the situation so that the easier choice is also the better one. In the studies we have, the effect is modest, reliable and almost entirely ignored by the people it describes. The measure that matters is not what people say about expertise but what they do when nobody is scoring.
