A new paper, by Chang-Tai Hsieh of the University of Chicago and three co-authors from the Chinese University of Hong Kong, finds that industrial output and investment have been consistently embellished. As a result, they argue that China overstated real GDP growth by two percentage points on average every year from 2008 to 2016 (see chart). Over time that adds up: official figures for 2016 would have exaggerated the size of the economy by 16%, or more than $1.5trn.