Written by Joseph Joyce

The recent research related to the trilemma (see here) confirms that policymakers who are willing to sacrifice control of the exchange rate or capital flows can implement monetary policy. For most central banks, this means using a short-term interest rate, such as the Federal Funds rate in the case of the federal reserve in the U.S. or the Bank of England's Bank Rate. But the record raises doubts about whether this is sufficient to achieve the policymakers' ultimate economic goals.

The short-term interest rate does not directly affect investment and other expenditures. But it can lead to a rise in long-term rates, which will have an effect on spending by firms and households. The relationship of short-term and long-term rates appears in the yield curve. This usually has a positive slope to reflect expectations of future short-term real rates, future inflation and a term premium. Changes in short-term rates can lead to movements in long-term rates, but in recent years the long-term rates have not always responded as central bankers have wished. Former Federal Reserve Chair Alan Greenspan referred to the decline in U.S. long-term rates in 2005 as a “conundrum.” This problem is exacerbated in other countries' financial markets, where long-term interest rates are affected by U.S. rates (see, for example, here andhere) and global factors.

Central banks that sought to increase spending during the global financial crisis by lowering interest rates faced a new obstacle: the zero lower bound on interest rates. Policymakers who could not lower their nominal policy rates any further have sought to increase inflation in order to bring down real rates. To accomplish, they devised a new policy tool, quantitative easing. Under these programs, central bankers purchased large amounts of bonds with longer maturities than they use for open market transactions and from a variety of issuers in order to bring down long-term rates. The U.S. engaged in such purchases between 2008 and 2014, while the European Central Bank and the Bank of Japan are still engaged in similar transactions. As a consequence of these purchases, the balance sheets of central banks swelled enormously.