Back in the late 1960s and early 1970s, as inflation was beginning to accelerate in the US, many economists pointed out that just looking at interest rates was not a good way to assess what central banks were doing. Low interest rates did not necessarily mean that central banks were pursuing easy money; and high interest rates did not necessarily mean that central banks were pursuing tight-money policies. One important piece showing this result was that by Dennis Starleaf and Jim Stephenson, which is reviewed here.
The point of their work was that interest rates might well be high (or rising) because the demand for lendable funds is high (or growing faster than the supply of lendable funds); similarly interest rates might be low because the demand for lendable funds is lower than expected and the excess quantity supplied of lendable funds has pushed interest rates downward. In other words, interest rates are determined by both supply and demand for lendable funds, not just by the supply, as controlled (or not!) by a central bank.
One of the early economists to forget the fundamentals of the previous paragraph was Joan Robinson, who seemed to completely ignore the effects of expected inflation on nominal interest rates. Here is a summary by Scott Sumner, as quoted by Robert Murphy:
The Joan Robinson interpretation
As you may
recall, I like to mock Joan Robinson’s statement that the German
hyperinflation could not possibly have been caused by easy money; after
all, nominal interest rates were not low in Germany during the early
1920s. I think it is fair to say that Joan’s views are no longer part
of the standard model. It is now widely believed that the German
hyperinflation was caused by easy money, and hence nominal interest
rates cannot be the right indicator for the stance of monetary policy.
When economists say “easy money” they can’t possibly be referring to
low nominal interest rates, otherwise they’d have to accept Joan rather
eccentric views.
Robinson ignored what I call "The Fisher Effect", namely that the nominal rate of interest increases with an increase in the expected rate of inflation due to both a reduction in supply and an increase in demand for lendable funds.
The problems with using the interest rate as an indicator of monetary ease or tightening just won't go away, nor will they be acknowledged during good times. Four years ago, while I was visiting the Bank of England with some students, we asked the person who told us about Bank policy why they focus on interest rates. She patiently explained that when the Bank increased the supply of money, interest rates would fall, etc. etc. without acknowledging that changes in the demand for lendable funds might also affect interest rates.
Three years ago during an informal session with current and former central bank economists visiting UWO to honour David Laidler, I asked the same thing. They gave pretty much the same answer. But when pressed, they acknowledged that changes in demand could also affect interest rates but argued that they didn't think it would be much of a problem since central banks in the UK, US, and Canada had been successfully targeting inflation rates for so long.
But it looks as if they got it wrong.
First, the supply of lendable funds grew faster than most people expected as foreign savings placed in the US grew. Second, the phenomenal growth of liquidity via shadow banks and off-balance-sheet operations in the early and middle portions of the decade kept the supply of lendable funds much greater than most of us could imagine. These two things kept interest rates low, but especially in the mortgage market, with the attendant spillover effects into the rest of the economy, and the resulting distortions that led to the housing boom and bust.
Following the housing bust, the demand for lendable funds shrank significantly. But at the same time, the supply of lendable funds shrank even more as 40% of the economy's liquidity dried up almost overnight with the near demise of the shadow banks. Interest rates fell, and even though they reached near zero for Fed Funds, they may not have fallen enough. Or, to be more precise, they may not have been a good indicator of the monetary ease (or tightening) by the Fed. The economy was in a recession and there was great uncertainty throughout the economy; thus the demand for lendable funds had plummeted. Focusing on just the interest rate as an indicator of central bank policy likely missed much of this reason for the decline in interest rates. [addendum: and as several of us pointed out back then, deciding to pay interest on commercial bank deposits at the Fed probably shrank the supply of lendable funds, offsetting whatever else the Fed was doing to pump liquidity into the markets.]
The Taylor Rule tries to account for both the supply of and demand for lendable funds by using a sort of reduced form equation to formulate interest rate policy. But if it doesn't point adequately to the sources of the changes in supply and demand (Taylor actually pooh-poohed the argument that there was a savings glut in the rest of the world in 2003-05 keeping US interest rates low, despite considerable evidence to the contrary), then it provides little if any, guidance for a central bank.
As with the use of the interest rate as an indicator of monetary policy, the Taylor Rule works well in a stable economy. But when there is a savings glut from abroad, and when there is a liquidity glut from shadow banks beyond the control of the central bank, unless the central bank has a really close awareness of what is happening to the supply and demand for lendable funds, interest rates won't provide much guidance.