The metric, which the Fed uses in guiding policy, reflects the extra compensation investors demand to hold longer-maturity debt instead of successive short-term securities. Treasuries have rallied in 2016 as the Fed held off on raising interest rates after liftoff from near zero in December, while central banks in Japan and Europe maintained unprecedented stimulus. “What I’m concerned about mostly is stagflation, meaning I think we’re seeing the very early signs of inflation beginning finally to pick up as the issue of deflation fades,” Greenspan, 90, said.