Big banks in recent years likely focused their refinance efforts on loans in agency MBS that had been purchased by the Federal Reserve, according to a working paper by economists at the Fed. John Kandrac and Bernd Schlusche noted that agency MBS held by the Fed exhibit faster prepayment rates than MBS held by the rest of the market. While some analysts have pinned the prepayments on refi activities by nonbanks, the Fed economists said they found that Bank of America, Citigroup, JPMorgan Chase and Wells Fargo played a large role in the high prepayment rates for agency MBS purchased by the Fed. The economists noted...