Some of the largest central banks, including the European Central Bank and the Bank of Japan, are starting to exit stimulus measures implemented to tackle the financial crisis. ECB President Jean-Claude Trichet said the central bank will start to withdraw liquidity initiatives. "There are all kinds of risks," said Jim O'Neill, Goldman Sachs' London-based chief global economist. "We don't know how much of the improvement in markets is due to central banks' largesse, and neither do they. They're pretty nervous, but they've got to get out of it at some stage."