A large-scale MBS purchase program has many of the benefits associated with purchases of longer-duration Treasury securities, such as inducing investors to shift to other assets, including bonds and equities. But it could also have more direct effects on the housing market. By increasing demand for MBS, such a program should reduce the effective yield on those MBS, which in turn should put downward pressure on mortgage rates. The aggregate demand effect should be felt not just in new home purchases, but also in the added purchasing power of existing homeowners who are able to refinance. Indeed, homeowners who refinance get the equivalent of a permanent tax cut. Concerns about central banks making sectoral credit allocation decisions are understandable in general. But here we are talking about a widely traded instrument in a sector that appears, now more than ever, to be central to the slow pace of recovery.