Real interest rates were low to a large extent because of global imbalances, the global saving glut and investment shortage. I believe that somewhat higher interest rates would have made little or no difference. Empirical evidence indicates that only a small portion of house-price increases can be attributed to monetary policy. 10 Bernanke (2010) shows that the recent phenomenon of a higher share of adjustable-rate mortgages was unlikely to have significantly increased the sensitivity of house prices to monetary policy. The availability of new, more exotic mortgage types mattered much more for initial mortgage payments than the level of shortterm interest rates. In my view, interest rates would probably have had to be raised very high so as to cause considerable damage to the real economy in order to stop the credit growth and housing boom. 11 That could have thrown the U.S. right into Japanese-style deflation and eventually a liquidity trap. Certainly, higher interest rates would have had no impact on the regulatory problems, distorted incentives and information problems mentioned above  7  I remember this period very vividly, because I was fortunate to have the opportunity to discuss and debate the problems of current monetary policy, deflation and liquidity traps in a group of great economists at Princeton University that included Ben Bernanke (before he left to be a Governor on the Federal Reserve Board), Alan Blinder, Paul Krugman, Chris Sims and Michael Woodford. 8  See Svensson (2003) for a discussion of policy options before and in a liquidity trap.
Interest rates that are high enough to have a noticeable effect on credit growth and asset prices may have strong negative effects on inflation and resource utilization, and a central bank will probably rarely have sufficient information about the likely beneficial longer-horizon effects on inflation and resource utilization for the trade-off to be worthwhile and motivated. 18  16  Walsh (2009) points out that when financial factors cause distortions, these distortions will in general introduce corresponding terms in a loss function for monetary policy that is a second-order approximation to household welfare. Curdia and Woodford (2009) present a model where the second-order welfare approximation is a standard quadratic loss function of inflation and the output gap between output and potential output, but where potential output is affected by financial factors. Then inflation and the output gap remain the target variables, with and without financial factors. The neutral rate in the model, that is, the real rate consistent with output equal to potential output, is then also affected by financial factors. 17  Adrian and Shin (2007, 2009) argue, in a model with a risk-taking channel as in Borio and Zhu (2008), that short interest-rate movements may have considerable effects on the leverage of securities broker-dealers in the market-based financial sector outside the commercial-banking sector. However, new regulation may affect the magnitude of these affects, and the size of the market-based financial sector may end up being smaller after the crisis. In Europe, the commercial banks dominate the financial sector.