US Treasury Secretary Janet Yellen said on Monday she will judge the success of President Joe Biden's coronavirus stimulus plan by how quickly it returns the economy to pre-pandemic levels of unemployment. Speaking to a New York Times Dealbook online event, Yellen also played down the increased debt levels that would be incurred from Biden's $1.9 trillion American recovery plan being debated in Congress. She said that due to low interest rates, US interest expenses as a share of GDP are at 2007 levels.