Fed's Yellen says research needed to understand inequality issue

More research is needed to understand what policies allow people to move up the economic ladder and what holds them back, Federal Reserve Chair Janet Yellen said on Thursday, returning to a controversial topic for the US central bank.

Yellen said that research may provide evidence of what allows people to get ahead, and to predict how individual circumstances impact income inequality.

"It would also be beneficial to understand whether any policies may hold people back or discourage upward mobility," Yellen said in prepared remarks for a speech to a Fed research conference here on economic mobility.

Yellen tackled the issue of income inequality in a speech in Boston last October, saying she was "greatly concerned" about income disparity in the US.