As has been widely discussed in the academic literature, one of the most important channels is the portfolio balance channel.5 This theory relies on the premise that financial assets are imperfect substitutes in investors’ portfolios, and, as a result, a rise in the demand for a particular financial asset relative to its supply – reflecting the Federal Reserve’s asset purchase programs, for example – will increase its price and reduce its yield. After selling that asset to the Federal Reserve, investors may rebalance their portfolios by investing in other assets, raising the prices of those assets, lowering their yields, and easing overall financial conditions. The Federal Reserve’s asset purchase programs were designed to remove risk from the portfolios of private investors. For example, Treasury and agency MBS purchases remove duration risk, thereby lowering longer-term interest rates and reducing private sector borrowing costs. Furthermore, agency MBS purchases also remove prepayment risk in the market. Since homeowners can prepay their mortgage at any time, MBS investors do not know when they will receive their cash flows. Investors generally demand an extra return to bear this risk, which is incorporated into MBS yields and in part passed along to borrowers. The removal of a considerable amount of this risk by the Fed’s purchases would be expected to lower MBS rates by lowering this extra return, thereby reducing primary mortgage rates, stimulating demand for housing and prompting increased refinancing activity.
In fact the issue of central bank independence, Ladies and Gentlemen, is as old as central banking itself, having been debated on and off over the past couple of hundred years. Many of the “transitional economies” of Eastern Europe also have adopted reforms aimed at  BIS Review 136/2007  1  making their central banks more independent. 19th and 20th century economists such as, David Ricardo and John Maynard Keynes have all added their views to the subject. There seem to be consensus that central banks must be given a charter which includes a strong commitment to price stability, and the freedom and sufficient scope to pursue it. This means that while central banks may not have goal independence, they should have instrument independence. One need not dwell on the desirability of price stability. Economies work better if investment and wage decisions are not thwarted and confused by high inflation. However, the fears in some respects are associated with the financing of fiscal deficits that governments in the developing world from time to time have to run to meet, for instance, social obligations or indeed provide public goods. This indeed is a genuine fear (including others that may be identified) that this symposium must address. There are arguments that there is a fundamental conflict between independence and an obligation to finance the budget deficit – a conflict which often is resolved at the expense of price stability.