ALAN GREENSPAN was a master of abstruse language as chairman of the Federal Reserve. “If you understood what I said, I must have misspoken,” he once joked. At least Mr Greenspan spoke. In China the central bank has made a habit of silence. Policy announcements are rare and, if they are offered, come at unpredictable hours, often over the weekend. Sudden shifts in the value of the yuan always bear the central bank’s fingerprints, but are infrequently explained. The motto for the People’s Bank of China (PBOC) should be: “If you know what we did, we must have done it wrong”.