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Federal Reserve Chair Janet Yellen has been awarded her second Yale University degree, a doctor of social science.

Yellen was honored Monday at the Ivy League school's 314th commencement. She received a Ph.D. in economics from Yale in 1971.

University President Peter Salovey praised Yellen's "wisdom, clarity and calm" in steering a financial course for the U.S.

He cited her research and work focusing on reducing unemployment and promoting "responsible economic growth" to improve people's lives.

The central bank's twin goals have been to promote maximum employment while controlling inflation.

Critics have argued that the Fed must worry more about prolonged low interest rates leading to possible bubbles in prices of assets such as stocks and real estate that could fall quickly, creating market instability when the Fed raises interest rates.