A close comparative look at the stimulus activity of the Federal Reserve suggests its support of the MBS market delivers more bang for the buck to the overall U.S. economy than its purchase of Treasury securities, according to a top Fed official. “[B]uying MBS has a different effect on the constellation of credit-market rates than buying Treasury securities,” Fed Governor Jeremy Stein said in a speech. Taking a look at what happened in the credit markets in the wake of the Fed Open Market Committee’s Sept. 13 announcement of a new program to purchase an additional $40 billion a month of agency MBS, Stein found...