This will be a brief but hopefully helpful column. For some time, I have been explaining that the new Fed operating framework for monetary policy, in which the FOMC essentially steers interest rates higher by fiat rather than in the traditional method (by managing the supply of funds and therefore the resulting pressure on reserves), is a really bad idea. But in responding to a reader's post I inadvertently hit on an explanation that may be clearer for some people than my analogy of a doctor manipulating his thermometer to give the right reading from the patient.
Right now, there is a tremendous surplus of reserves above what banks are required to hold or desire to hold. With free markets, this would result in a Fed funds interest rate of zero, or even lower under some circumstances, with a substantial remaining surplus. In this case, the Fed funds effective rate has tended to be in the 10-20bps range since the Fed started paying interest on excess reserves (IOER).
So what happens when there is a floor price established above the market-clearing price? Economics 101 tells us that this results in surplus, with less exchange and higher prices than at equilibrium. Consider a farm-price support program where the government establishes a minimum price for cheese (as it has, actually, in the past). If that price is below the natural market-clearing price, then the floor has no effect. But if the price is above the natural market-clearing price, as in the chart below where the minimum cheese price is set at a, then in the market we will see a quantity of cheese traded equal to b, at a price of a.
But what also happens is that producers respond to the higher price by producing more cheese, which is why the supply curve has the shape it does. In order to keep this excess cheese from pushing market prices lower, the government ends up buying c-b cheese at some expense that ends up being a transfer from government to farmers. It can amount to a lot of cheese. This is the legacy of farm price supports: vast warehouses of products that the government owns but cannot distribute, because to distribute them would push prices lower. So the government ends up distributing them to people who wouldn't otherwise buy cheese, at a zero price. And eventually, we get the Wikipedia entry "government cheese." https://en.wikipedia.org/wiki/Government_cheese
Now, this is precisely what has happened with the artificial price support for overnight interest rates. Whatever the clearing interest rate is with the current level of reserves, it is lower than the 0.25% IOER (and we know this, among other ways, because there are excess reserves. If the price floating to the actual clearing price, then there would be no excess reserves, although the mechanism for this result is admittedly more confusing than it is for cheese). So the Federal Reserve is forced to "buy up the surplus reserves" by paying interest on these reserves; this amounts to a transfer from the government to banks, rather than to farmers in the cheese example.
You should realize too that setting the floor rate higher than the market-clearing rate artificially reduces the volume of trade in reserves. The chart below, which comes from this article on the New York Fed's blog, illustrates this nicely.
Creating such a floor also causes the supply of excess reserves themselves to increase beyond what it would otherwise be. This confusing result derives because while the Fed supplies the total reserves number to the market, banks can choose to create more "excess" reserves by doing less lending, or can create fewer excess reserves by doing more lending. Of course, banks aren't deciding to create excess reserves per se; they are deciding whether it is more advantageous to make a loan or to earn risk-free money on the excess reserves. A higher floor rate implies less lending, all else equal - and, as I have said in the past, this means the Fed could cause a huge increase in bank lending by setting IOER at a penalty rate. This would create the conditions necessary for these lines to cross in negative nominal interest rate territory, with much higher volumes of credit and much lower levels of excess reserves being the result.
In this environment, and as recognized by the Sack-Gagnon framework that is now the presumed operating framework for Fed policy, raising IOER is the only way to change the overnight interest rates unless the Desk undertakes to shift the entire supply curve heavily to the left, by draining trillions in reserves. But raising IOER, just like raising the floor price of cheese, will create more imbalances: bigger excess reserves, less lending, and a bigger transfer from government to banks.
(Note: this is subtly different from what I have said before, which is that raising IOER will have no effect on the growth rate of the transactional money supply. Depending on the shape of the supply curve, it will reduce lending which in turn may reduce the growth rate of the monetary aggregates that we care about, such as M2. My suspicion is that the supply curve is in fact pretty steep, meaning that banks are relatively insensitive to small changes in rates, and thus loans and hence the monetary aggregates won't see much change in the rate of growth - or, more likely, any change will be the result of other effects beyond this one such as the effect of general economic prospects on the quality of credits and the demand for loans).
Price supports, as any economist can tell you, are an inefficient way to subsidize an industry. And in fact, I don't think the Fed is really interested in subsidizing banks at this stage in the cycle: they seem to be doing just fine. But they are taking on all of these imbalances, creating all of this government cheese, because they believe the effects I talk about parenthetically above are quite large, rather than vanishingly small as I believe. And the ancillary effect, by raising interest rates, is to spur money velocity - an unmitigated negative in this environment, as it will push inflation higher.
Now, all of this discussion may be moot since the current betting is that the Fed won't raise interest rates any time soon. But it is good to understand this mechanism as clearly as we can, so that we can prepare ourselves for those effects when they occur.
 It is really hard to say how low interest rates would go, and/or how much surplus would remain, because we have no idea at all what the supply and demand curves for funds look like at sub-zero rates. Most likely there is a discontinuity at a zero rate, but how much of one and the elasticities of supply and demand below zero are likely to be "weird."
 In fact, in high school I won an economics prize for my paper "That's a Lotta Cheese." No joke.
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