Program will spur growth and cut unemployment, Fed chairman says.

Fed links duration, extent of QE3 to 'sustained improvement' in jobs market.

Fed links duration, extent of QE3 to 'sustained improvement' in jobs market.

Fed Chairman cites unemployment as a 'grave concern' in Jackson Hole speech.

Fed Chairman cites unemployment as a 'grave concern' in Jackson Hole speech.

Central bank stands ready to take more action to boost recovery, Fed chairman says.

Central bank stands ready to take more action to boost recovery, Fed chairman says.

With high U.S. unemployment and financial stress in Europe, the Fed is expected to move toward a risk management strategy.