Krugman’s blog, 9/1/15

There were four posts yesterday.  The first was “Gravity:”

Now that’s fun: Adam Davidson tells us about trade in the ancient Near East, as documented by archives found in Kanesh — and reports that the volume of trade between Kanesh and various trading partners seems to fit a gravity equation: trade between any two regional economies is roughly proportional to the product of their GDPs and inversely related to distance. Neat.

But what does the seemingly universal applicability of the gravity equation tell us? Davidson suggests that it’s an indication that policy can’t do much to shape trade. That’s not where I would have gone, and it’s not where those who have studied the issue closelyhave gone.

Here’s my take: Think about two cities with the same per capita GDP — we can relax that assumption in a minute. They will trade if residents of city A find things being sold by residents of city B that they want, and vice versa.

So what’s the probability that an A resident will find a B resident with something he or she wants? Applying what one of my old teachers used to call the principle of insignificant reason, a good first guess would be that this probability is proportional to the number of potential sellers — B’s population.

And how many such desirous buyers will there be? Again applying insignificant reason, a good guess is that it’s proportional to the number of potential buyers — A’s population.

So other things equal we would expect exports from B to A to be proportional to the product of their populations.

What if GDP per capita isn’t the same? You can think of this as increasing the “effective” population, both in terms of producers and in terms of consumers. So the attraction is now the product of the GDPs.

Is there anything surprising about the fact that this relationship works pretty well? A bit. Standard pre-1980 trade theory envisaged countries specializing in accord with their comparative advantage — England does cloth, Portugal wine. And these models suggest that how much countries trade should have a lot to do with whether they are similar or not. Cloth exporters shouldn’t be selling much to each other, but should instead do their trading with wine exporters. In reality, however, there’s basically no sign of any such effect: even seemingly similar countries trade about as much as a gravity equation says they should.

Calibrated models of trade have long dealt with this reality, somewhat awkwardly, with the so-called Armington assumption, which simply assumes that even the apparently same good from different countries is treated by consumers as a differentiated product — a banana isn’t just a banana, it’s an Ecuador banana or a Saint Lucia banana, which are imperfect substitutes. The new trade theory some of us introduced circa 1980 — or as some now call it, the “old new trade theory” — does a bit more, and possibly better, by introducing monopolistic competition and increasing returns to explain why even similar countries produce differentiated products.

And there’s also a puzzle about both the effect of distance and the effect of borders, both of which seem larger than concrete costs can explain. Work continues.

Does any of this suggest the irrelevance of trade policy? Not really. Changes in trade policy do have obvious effects on how much countries trade. Look at what happened when Mexico opened up starting in the late 1980s, as compared with Canada, which was fairly open all along — and which, like Mexico, mainly trades with the US:

So what does gravity tell us? Simple Ricardian comparative advantage is clearly incomplete; the process of international trade is subtler, with invisible as well as visible costs. Not trivial, but not too unsettling. And gravity models are very useful as a benchmark for assessing other effects.

The second post yesterday was “Multipliers: What We Should Have Known:”

There’s a very nice interview with Olivier Blanchard, who is leaving the IMF, in which among other things Olivier says the right thing about changing one’s mind:

With respect to outside, the issue I have been struck by is how to indicate a change of views without triggering headlines of “mistakes,’’ “Fund incompetence,’’ and so on. Here, I am thinking of fiscal multipliers. The underestimation of the drag on output from fiscal consolidation was not a “mistake’’ in the way people think of mistakes, e.g., mixing up two cells in an excel sheet. It was based on a substantial amount of prior evidence, but evidence which turned out to be misleading in an environment where interest rates are close to zero and monetary policy cannot offset the negative effects of budget cuts. We got a lot of flak for admitting the underestimation, and I suspect we shall continue to get more flak in the future. But, at the same time, I believe that we, the Fund, substantially increased our credibility, and used better assumptions later on. It was painful, but it was useful.

Indeed. There are a lot of people out there whose idea of a substantive argument is “you used to say X, now you say Y” — never mind the reasons why you changed your view, and whether it was right to do so.It’s important not to fall into the trap of being afraid to let new evidence or analysis speak.

One thing I would say, however, is that on this particular issue the Fund should have known better. Olivier says that the evidence “turned out to be misleading in an environment where interest rates are close to zero and monetary policy cannot offset the negative effects of budget cuts”, but didn’t we know that? I certainly did.

And let me also beat one of my favorite drums: the prediction that multipliers would be much larger in a liquidity trap came out of IS-LMish macro (or, to be fair, New Keynesian models) and has been overwhelmingly confirmed by experience. So this was yet another victory for Keynesian analysis, the success story nobody will believe.

Yesterday’s third post was “The Triumph of Backward-Looking Economics:”

We don’t get to do many controlled experiments in economics, so history is mainly what we have to go on. Unfortunately, many people who imagine that they know how the economy works go with what they think they heard about history, not with what actually happened. And I’m not just talking about the great unwashed; quite a few well-known economists seem not to have heard about FRED, or at least haven’t picked up the habit of doing a quick scan of the actual data before making assertions about facts.

And there’s one decade in particular where people are weirdly unaware of the realities: the 1980s. A lot of this has to do with Reaganolatry: the usual suspects have repeated so often that it was a time of extraordinary, incredible success that I often encounter liberals who believe that something special must have happened, that somehow the events were at odds with what the prevailing macroeconomic models of the time said would happen.

But nothing special happened, aside from the unexpected willingness of the Fed to impose incredibly high unemployment in order to bring inflation down.

What did orthodox salt-water macroeconomists believe about disinflation on the eve of the Volcker contraction? As it happens, we have an excellent source document: James Tobin’s “Stabilization Policy Ten Years After,” presented at Brookings in early 1980. Among other things, Tobin laid out a hypothetical disinflation scenario based on the kind of Keynesian model people like him were using at the time (which was also the model laid out in the Dornbusch-Fischer and Gordon textbooks). These models included an expectations-augmented Phillips curve, with no long-run tradeoff between inflation and unemployment — but expectations were assumed to adjust gradually based on experience, rather than changing rapidly via forward-looking assessments of Fed policy.

This was, of course, the kind of model the Chicago School dismissed scathingly as worthy of nothing but ridicule, and which was more or less driven out of the academic literature, even as it continued to be the basis of a lot of policy analysis.

So here was Tobin’s picture:

Here’s what actually happened:

Unemployment shot up faster than in Tobin’s simulation, then came down faster, because the Fed didn’t follow the simple rule he assumed. But the basic shape — a clockwise spiral, with inflation coming down thanks to a period of very high unemployment — was very much in line with what standard Keynesian macro said would happen. On the other hand, there was no sign whatsoever of the kind of painless disinflation rational-expectations models suggested would happen if the Fed credibly announced its disinflation plans.

So how does the decade of the 1980s end up being perceived as a defeat for Keynesians? To see it that way you have to systematically misrepresent both what happened to the economy and what people like Tobin were saying at the time. In reality, Tobinesque economics looks very good in the light of events.

The last post yesterday was “Bad Ideas Down Under:”

I’m heading off to Sydney, for the Festival of Dangerous Ideas. Blogging will be limited due to travel, plus blood rushing to my head from standing upside down when I get there.




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