Labor markets are hampered by the effects of the Great Recession and the Federal Reserve should move cautiously in deciding when to raise interest rates, Fed Chair Janet Yellen said on Friday. In a speech at an economic conference in Jackson Hole, Wyoming, she said the unemployment rate alone is inadequate to evaluate the strength of the job market. The jobless rate has fallen faster than expected, but Yellen said the economic disruption of the last five years has left millions of workers sidelined, discouraged, or stuck in part time jobs. Yellen argued for a "pragmatic" approach that allows officials to evaluate data without committing to a preset policy. The Fed has held benchmark rates near zero since December 2008, and said it would wait a "considerable time" after winding down a bond-buying program in October before raising them. Financial markets currently expect rates to raise around the middle of next year.