Don’t try this at home: seek professional advice. A sound maxim, one might think. Unless you know something about electrical wiring, get an electrician in; go to a doctor rather than diagnosing yourself. And, since you are a fallible investor, choose your financial portfolio with the help of an investment adviser.

But do typical investment advisers give good investment advice? Three economists recently published research exploring this question in an intriguing fashion – they mixed the experimental methods of a double-blind controlled trial with the latest behavioural economics, all seasoned with a dash of tabloid sting.

The researchers recruited professional mystery shoppers and asked them to seek advice from a variety of financial advisers in Massachusetts. Each mystery shopper was equipped with one of four imaginary portfolios.