We have long grown accustomed to Chinese fakes. Fake watches. Fake DVDs. Even, recently, a fake Goldman Sachs. But what if something more fundamental were fake? What if China’s gross domestic product numbers were not all they were cracked up to be?

Many economists have long suspected precisely that. For one thing, China’s data for GDP growth have been suspiciously smooth. While most economies are subject to booms and busts, China’s has seemed to sail on regardless.

Another cause for doubt is that provincial figures and national data don’t always add up. Nor, often, do Chinese trade statistics matched against those of its trading partners. Such discrepancies are partly down to the sheer difficulty of measuring activity in such a vast country. Partly, though, they result from perverse incentives through which officials have been rewarded according to crude measures of growth.