A theory of house temperatures By Scott Sumner

Bob Murphy has occasionally complained that I contradict myself on interest rates. I frequently say:

1. Interest rates are a meaningless indicator of the current stance of monetary policy.

2. Raising interest rates makes monetary policy more contractionary, on the day they were raised.

In fact there is no contradiction, but since lots of people (not just Bob) are confused on this point, I’ll use a house temperature analogy. Of course this will be done half-jokingly, Bob doesn’t actual hold the views about house temperatures that I will attribute to him, but hopefully the example will make it easier to see my point:

1. Suppose that on average houses are 68 degrees in the winter, and 78 degrees in the summer. People use heat in the winter, but since they are wearing winter clothing they only heat their house up to 68 degrees. People use AC in the summer, but since they are wearing summer clothing they only AC it down to 78. I think that this is a plausible assumption. House temps then represent the “stance” of house temperature policy, equivalent to the stance of monetary policy.

2. Suppose that turning up the thermostat makes houses warmer. And turning on the AC cools temps in the summer. Since turning up the thermostat raises temps, consider it analogous to an expansionary monetary policy “gesture”. And vice versa for AC. Adjusting the AC or thermostat then represents raising and lowering the fed funds target.

Bob Murphy’s theory of temperature would be that when people are frequently turning up the thermostat, you can expect houses to be relatively warm. And when people are frequently turning on the AC, you can expect houses to be cool. The Sumner theory is that when people are most frequently turning up the thermostats, houses will be relatively cool, even though that action makes them warmer. Bob Murphy’s theory is that houses are relatively warm in the winter, because people frequently turn up their thermostats in the winter. Sumner’s theory is that houses will be relatively cool in the winter, despite the fact that people turn up the thermostat more frequently in the winter, and despite the fact that turning up the thermostat does in fact make houses warmer, ceteris paribus. Bob Murphy will claim that Sumner contradicts himself on house temperatures.

I don’t want to claim that pushing up the thermostat always indicates a cool house, even though it’s highly correlated, because there are occasions where you push it up long enough to actually make the house warm, even in winter. But if you put a gun to my head, and asked me whether thermostat pushing is more likely to imply the house is cool or warm, I’d say cool, even though the action makes houses warmer. But most often I’d simply say that looking at how people fiddle with the thermostat controls is not a good way of judging the temperature inside a house.

Milton Friedman understood this distinction:

Low interest rates are generally a sign that money has been tight, as in Japan; high interest rates, that money has been easy.

Notice the past tense “has been tight”. He knew that low rates did not necessarily imply that money was tight at that moment.

Similarly, if I was told that my neighbor had adjusted the thermostat higher 10 times in the past month, I’d assume it was winter and his house was relatively cold, even though that action made it warmer. If I was told he’d switched on the AC 10 times in the past month, I’d assume his house was relative warm, even though that action made the house colder.

Now suppose you naively looked at the correlation and assumed that turning up the thermostat actually made the houses cooler. Obviously no one in his or her right mind (except perhaps NeoFisherians) would hold that view. But let’s say you did. In that case you’d end up turning up the thermostat in the middle of summer. This may be why no NeoFisherian has ever been put in charge on a central bank.

But even real world central bankers make mistakes with the thermostat. And it is partly because of exactly the fallacy that I am suggesting that Bob Murphy may suffer from. I’m up to page 410 in the Bernanke memoir, and even he seems to be confused (although when Bernanke was an academic he was fully aware of the argument that I am making here.) As a central banker, Bernanke suggested that the Fed eased monetary policy in 2008, because they frequently cut rates. In my view that’s only true of January, where the rates were probably cut faster than the Wicksellian interest rate fell. But not the other 11 months, when the Wicksellian equilibrium rate fell faster. He was turning up the monetary thermostat, but the outside temperature fell so rapidly that the house was actually getting colder. He ended up with a “cool house policy stance.”

Bernanke himself uses a “cold wind” analogy in his memoir. The cold wind in my example represents the falling Wicksellian equilibrium rate. Bernanke did not turn up the thermostat aggressively enough to offset the falling outside temps. Even worse (and here’s where the analogy finally breaks down) the Fed actually caused the cold wind by an excessively passive policy in 2008 that unintentionally tightened policy, which lowered NGDP growth, and hence lowered the Wicksellian equilibrium rate.

Back in 2003, Bernanke claimed that interest rates were not a good indicator of the stance of monetary policy. Nor was the money supply. Instead, he insisted that you had to look at NGDP growth and inflation. He was correct. But as Fed chair he switched to the popular view that interest rates (and perhaps base expansion after 2009) were the best indicators. Thus he viewed monetary policy as being quite accommodative after 2008, when it was exactly the opposite.

To summarize, the thermostat is like the fed funds target (or the base if you are a monetarist), and NGDP growth is like the temperature inside the house. The outside temperature is like the Wicksellian equilibrium rate (if you are a Keynesian) or like velocity (if you are a monetarist.) The popular view is that the “temperature policy” of the owner is best described by the amount and type of fiddling with thermostats and AC controls, whereas the sophisticated view is that the temperature policy stance is best described by the house’s inside temperature. That’s the view that Bernanke used to hold, until he became a central banker. This paper by Vasco Curdia uses the sophisticated view, and shows that Bernanke is wrong about policy being accommodative after 2008.

If you are not sick of the analogy yet, we could also apply it to monetary policy failure at the zero bound. Keynesians would blame the “liquidity trap.” What’s the temperature analogy for the zero bound? Some would say a furnace that is out of fuel. But a better analogy is a furnace too small to fight against the bitter cold front that swept down from Canada, even going full blast.

The monetarist view is that a “fiat furnace” can never be too small. It can raise temperatures up to an almost infinite level, or at least up to 100 trillion degrees.

PS. I’m pretty sure I stole some of these metaphors from old Nick Rowe posts.

Update: Michael Byrnes has sent me a Nick Rowe post using the thermostat metaphor. He got it from Milton Friedman, but I’d guess the post I linked to is superior to whatever Friedman said about the subject.

Update#2: Market Fiscalist noticed a flaw, and suggested an improvement: