File photo shows Vice Chairwoman of the US Federal Reserve (Fed) Janet Yellen testifying during her nomination hearing to chair the Federal Reserve before the Senate Banking Committee on Capitol Hill in Washington D.C., capital of the United States, Nov. 14, 2013. The US Senate confirmed Janet Yellen as the next head of the Federal Reserve on Jan. 6, 2014. She would replace outgoing Fed Chairman Ben Bernanke whose term ends at the end of this month. (Xinhua/Zhang Jun)   

File photo shows Vice Chairwoman of the US Federal Reserve (Fed) Janet Yellen testifying during her nomination hearing to chair the Federal Reserve before the Senate Banking Committee on Capitol Hill in Washington D.C., capital of the United States, Nov. 14, 2013. The US Senate confirmed Janet Yellen as the next head of the Federal Reserve on Jan. 6, 2014. She would replace outgoing Fed Chairman Ben Bernanke whose term ends at the end of this month. (Xinhua/Zhang Jun) 

Janet Yellen (R), US Federal Reserve vice chairwoman, speaks while US President Barack Obama looks on during her nomination ceremony at the White House in Washington D.C., in this file photo taken on Oct. 9, 2013. The US Senate confirmed Janet Yellen as the next head of the Federal Reserve on Jan. 6, 2014. She would replace outgoing Fed Chairman Ben Bernanke whose term ends at the end of this month. (Xinhua/Zhang Jun) 

File photo shows (R-L) US Federal Reserve (Fed) Chairman Ben Bernanke, former Fed heads Alan Greenspan and Paul Volker, Vice Chairwoman and incoming Chairwoman Janet Yellen attending the US Federal Reserve centennial commemoration at the Federal Reserve building in Washington D.C., capital of the United States, Dec. 16, 2013. The US Senate confirmed Janet Yellen as the next head of the Federal Reserve on Jan. 6, 2014. She would replace outgoing Fed Chairman Ben Bernanke whose term ends at the end of this month. (Xinhua/Zhang Jun)