Are you smarter than a ten-year-old? New data suggest that a shockingly large portion of adults in the rich world might not be. Roughly one-fifth of people aged 16 to 65 perform no better in tests of maths and reading than would be expected of a pupil coming to the end of their time at primary school, according to a study released on December 10th by the OECD, a club of mostly rich countries. Worse still, adults in many places have grown less literate over the past ten years.