Falling US shares tell us only that investors were overexcited in January

If you were the incoming or retiring chairman of the Federal Reserve, you might be quietly pleased to see stock markets plunge on the day of the handover. As Jerome Powell was sworn in on Monday to succeed Dr Janet Yellen as head of America’s central bank, the Dow Jones index of leading US stocks was falling by a one-day record of 1,175 points, with Asian, European and London markets following overnight.