Tag: Economic Modeling

A semi-platonic dialogue about secular stagnation, asymmetric risks, Federal Reserve policy, and the role of model-building in guiding economic policy

Posted on by Brad DeLong
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Sokrates: You remember how I used to say that only active dialogue–questions-and-answers, objections-and-replies–could convey true knowledge? That a flat wax tablet covered by written words could only convey an inadequate and pale simulacrum of education?

Aristoteles: Yes. And you remember how I showed you that you were wrong? That conversation is ephemeral, and very quickly becomes too confused to be a proper educational tool? That only something like an organized and coherent lecture can teach? And only something like the textbooks compiled by my lecture notes can make that teaching durable?

Aristokles: But, my Aristoteles, you never mastered my “dialogue” form. My “dialogue” form has all the advantages of permanence and organization of your textbooks, and all the advantages of real dialectic of Sokrates’s conversation.

Sokrates: How very true, wise Aristokles!

Aristokles How am I to take that?

Xanthippe: You now very well: as snark, pure snark. That’s his specialty.

Hypatia: This is all complicated by the fact that in the age of the internet real, written, permanent dialogues can spring up at a moment’s notice:

Sokrates: And with that, let’s roll the tape:

Other things linked to that are highly relevant and worth reading:

Things I did not find and place outbound links to, but should have:

  • Polya
  • Dennis Robertson
  • Donald Patinkin

Looking at the whole thing, I wince at how lazy people–especially me–have been with their weblog post titles. I should find time to go back and retitle everything, perhaps adding an explanatory sentence to each link…

MOAR musings on whether we consciously know more or less than what is in our models…

Posted on by Brad DeLong

Larry Summers presents as an example of his contention that we know more than is in our models–that our models are more a filing system, and more a way of efficiently conveying part of what we know, than they are an idea-generating mechanism–Paul Krugman’s Mundell-Fleming lecture, and its contention that floating exchange-rate countries that can borrow in their own currency should not fear capital flight in a utility trap. He points to Olivier Blanchard et al.’s empirical finding that capital outflows do indeed appear to be not expansionary but contractionary:

Olivier Blanchard et al.: Macro Effects of Capital Inflows: Capital Type Matters: “Some scholars view capital inflows as contractionary…

…but many policymakers view them as expansionary. Evidence supports the policymakers…. Bond inflows lead to currency appreciation and are contractionary, while non-bond inflows lead to an appreciation but also to a decrease in the cost of borrowing, and thus may be expansionary…. How can we reconcile the models and reality? … Capital inflows may… reduce the cost of financial intermediation… be expansionary even for a given policy rate. In emerging markets, with a relatively underdeveloped financial system, the effect of a reduction in the cost of financial intermediation may dominate, leading to a credit boom and an output increase despite the appreciation….

The appropriate policies vis-à-vis capital inflows depend very much on the nature of the inflows. Sterilised foreign exchange (FX) market intervention… used in response to non-bond inflows… increases capital inflows, and thus increases the effects of inflows on credit and the financial system…. If the central bank is worried about both appreciation and unhealthy or excessive credit growth, FX intervention or capital controls are preferable to the use of the policy rate in response to an increase in bond inflows…. In response to non-bond inflows, our framework suggests that if the goal is to maintain exchange rate stability with minimum impact on the return to non-bonds, capital controls do the job best, followed by FX intervention, followed by a move in the policy rate…

If you asked me for a precis of what is going on in Blanchard et al., I would start drawing a graph in which we had:

  1. An IS (“Investment-Savings”) curve, for which the level of production (a) increases when government purchases increase; (b) falls when the long-term risky real interest rate rises, discouraging investment and consumption directly and discouraging exports indirectly by raising the value of the currency; and (c) falls when desired capital inflows rise and thus raise the value of the currency.
  2. An LM (“Liquidity-Money) curve, relating demand for money and thus the short-term safe nominal interest rate as a function of the level of output given the money stock.
  3. A CC (“Credit-Channel) wedge between the two, consisting of (a) the term premium on interest rates, that is how much long-term rates exceed short-term rates; (b) the risk premium on investments; and (c) the expected inflation rate:
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I would point out that, in Blanchard et al.‘s setup, what they call “bond inflows” move the IS curve to the left by raising the value of the currency for any given short-term safe nominal policy interest rate. Thus they are contractionary–for a constant policy interest rate on the LM curve, and a constant double-arrow CC credit-channel wedge.

I would point out that what they call “nonbond inflows” both move the IS curve to the left and shrink the double-arrow CC credit-channel wedge. So–for a constant policy rate–are contractionary if the first and expansionary if the second effect dominates.

And I would point out that Krugman’s Mundell-Fleming lecture deals with this case under the heading of “banking crisis”:

Banking crisis: Several commentators – for example, Rogoff (2013) — have suggested that a sudden stop of capital inflows provoked by concerns over sovereign debt would inevitably lead to a banking crisis, and that this crisis would dominate any positive effects from currency depreciation. If correct, this would certainly undermine the optimism I have expressed about how such a scenario would play out. The question we need to ask here is why, exactly, we should believe that a sudden stop leads to a banking crisis. The argument seems to be that banks would take large losses on their holdings of government bonds. But why, exactly? A country that borrows in its own currency can’t be forced into default, and we’ve just seen that it can’t even be forced to raise interest rates. So there is no reason the domestic-currency value of the country’s bonds should plunge. The foreign-currency value of those bonds may indeed fall sharply thanks to currency depreciation, but this is only a problem for the banks if they have large liabilities denominated in foreign currency…

Krugman is working in a framework in which the risk-premium part of the credit channel–the risk-premium part of the double-headed orange CC arrow–is small in normal times but can discontinuously shift to large in the event of a “banking crisis”. For Blanchard et al. and Summers, the size of the risk-premium part of the CC arrow is not discontinuously 0-1, but rather moves gradually with “confidence”: low when confidence is high and desired capital inflows are large, high when confidence is low and there is a sudden stop. Krugman says that since, in the absence of large foreign currency-denominated debt, there is no reason for there to be fears of a banking crisis in the event of a sudden stop.

Blanchard et al. appear to think that Krugman is largely right about developed economies. In them risk premiums are, they think, relatively small: financial markets work relatively well, and are not all that sensitive to amounts of new investment money flowing in. But, they say, they believe that in developing economies things are different. There, they believe, the risk premium component of the credit channel wedge is sensitive to international market conditions and thus the size the desired capital inflow.

In brief, Blanchard et al appear to think that only developing economies are “Minskyite” in the sense of a strong vulnerability of the CC risk premium to “confidence” even in the absence of fundamental shocks. Summers’s judgment appears to be that all economies are “Minskyite”. If I understand Paul’s thinking, it is more that “confidence” is only likely to matter as an equilibrium-selection device in a model with multiple equilibria like that of Krugman’s (1999b) third-generation financial-crisis model in “Balance Sheets, the Transfer Problem, and Financial Crises”. No multiple equilibrium, no possibility of suddenly jumping to a bad equilibrium, and so little possibility of any sort of pure “confidence” shock causing large amounts of trouble.

Paul here is more on the “financial markets work like they ought to” side of the argument. Olivier and company are more on the side of “developing economies have financial-market vulnerabilities North Atlantic economies do not” side. And Summers is more on the side of Keynes here:

Enterprise only pretends to itself to be mainly actuated by the statements in its own prospectus…. Only a little more than an expedition to the South Pole, is it based on an exact calculation of benefits to come. Thus if the animal spirits are dimmed and the spontaneous optimism falters, leaving us to depend on nothing but a mathematical expectation, enterprise will fade and die…. This means, unfortunately, not only that slumps and depressions are exaggerated in degree, but that economic prosperity is excessively dependent on a political and social atmosphere which is congenial to the average business man. If the fear of a Labour Government or a New Deal depresses enterprise, this need not be the result either of a reasonable calculation or of a plot with political intent;–it is the mere consequence of upsetting the delicate balance of spontaneous optimism. In estimating the prospects of investment, we must have regard, therefore, to the nerves and hysteria and even the digestions and reactions to the weather of those upon whose spontaneous activity it largely depends…

(Early) Monday DeLong Smackdown: Larry Summers on how we know more than we write down in our lowbrow (or highbrow) economic models

Posted on by Brad DeLong

Larry Summers: Thoughts on Delong and Krugman Blogs: “I think the issue is more on the supply side than the demand side…

…If I believed strongly in the vertical long run Phillips curve with a NAIRU around five percent and in inflation expectations responsiveness to a heated up labor market, I would see a reasonable case for the monetary tightening that has taken place. I am sure Paul and Brad are right that a desire to be ‘sound’ also influences policy.  I am not nearly as hostile to this as Paul. I think maintaining confidence is an important part of the art of policy.

A good example of where market thought is, I think, right and simple model based thought is I think dangerously wrong is Paul’s own Mundell-Fleming lecture on confidence crises in countries that have their own currencies.  Paul asserts that a damaging confidence crisis in a liquidity trap country without large foreign debts is impossible, because if one developed the currency would depreciate, generating an export surge.

Paul is certainly correct in his model, but I doubt that he is in fact. Once account is taken of the impact of a currency collapse on consumers’ real incomes, on their expectations, and especially on the risk premium associated with domestic asset values, it is easy to understand how monetary and fiscal policymakers who lose confidence and trust see their real economies deteriorate, as Olivier Blanchard and his colleagues have recently demonstrated.  Paul may be right that we have few examples of crises of this kind, but if so this is, perhaps, because central banks do not in general follow his precepts.

I do not think this is a pressing issue for the US right now. But the idea that policymakers should in general follow the model and not worry about considerations of market confidence seems to me as misguided as the view that they should be governed by market confidence to the exclusion of models.

Larry is taking the side that our economists’ models are primarily filing systems rather than truth-generating mechanisms. As I have already written twice in the past week, the question is: Are models properly idea-generating machines, in which you start from what you think is the case and use the model-building process to generate new insights? Or are models merely filing systems–ways of organizing your beliefs, and whenever you find that your model is leading you to a surprising conclusion that you find distasteful the proper response is to ignore the model, or to tweak it to make the distasteful conclusion go away?

Both can be effectively critiqued. Models-as-discovery-mechanisms suffer from the Polya-Robertson problem: It involves replacing what he calls “plausible reasoning”, where models are there to assist thinking, with what he calls “demonstrative reasoning”. in which the model itself becomes the object of analysis. The box that is the model is well described but, as Dennis Robertson warned,there is no reason to think that the box contains anything real. Models-as-filing-systems are often used like a drunk uses a lamp post: more for support than illumination.

In the real world, it is, of course, the case that models are both: both filing systems and discovery mechanisms. Coherent and productive thought is, as the late John Rawls used to say, always a process of reflective equilibrium–in which the trinity of assumptions, modes of reasoning, and conclusions are all three revised and adjusted under the requirement of coherence until a maximum level of comfort with all three is reached. The question is always one of balance.

The particular fight Larry wants to pick this weekend is over Paul Krugman’s Mundell-Fleming lecture, and Paul’s claim that a floating-rate sovereign that borrows in its own currency and is in a liquidity trap should not worry about maintaining “confidence”. Paul’s argument is that, in the model, pursuing aggressive expansionary policies will eat first to currency depreciation, then to an export boom, then to full employment, and only then will any downsides emerge. Thus the process can be stopped before it begins to generate risks. And it is only after full employment is attained that policy concern should shift to avoiding such risks.

Larry, however, says: We know things that are not in the model. Those things make Paul’s claim wrong.

My problem with Larry is that I am not sure what those things are. Paul notes that in normal times–away from the interest-rate zero lower bound–a loss of “confidence” in a country that floats its and borrows in its own currency an be contractionary:

Now,,, we can examine the effect of a loss of investor confidence… which we can view as a sudden stop… reduction in capital inflows at any given interest and exchange rate…. What would happen to a country with its own currency and a floating rate confronted with a foreign loss of confidence?… The depreciation of the currency at any given interest rate would increase net exports, and hence shift the IS curve out. This might be the end of the story. As I noted… however, the central bank might be concerned about the possible inflationary consequences of depreciation, and would therefore lean against it; in that case the MP schedule would shift up. So interest rates would rise due to rising demand for domestic goods and, possibly, tight money driven by inflation concerns. It is possible, if the latter motive is strong enough, that output could actually fall…

But, Paul says, at the zero lower bound things are different because the central bank has a cushion between what it wants the real interest rate to be and what the zero lower bound forces the real interest rate to be:

Right now the United States, the United Kingdom, and Japan are all stuck in the liquidity trap…. [with] policy… constrained by the zero lower bound…. This in turn means that any shift in the MP schedule, unless very large, won’t lead to a rise in interest rates…. All that matters is the rightward shift in the IS curve…. In short, under current conditions the much-feared loss of confidence by foreign investors would be unambiguously expansionary, raising output and employment in nations like the United States, the United Kingdom, and Japan…

It’s not clear what we know that is not in the model that would reverse this conclusion of Paul’s in the case of a floating exchange rate in a country that borrows in its own currency and happens to be in a liquidity trap. Paul notes that his conclusion goes against market wisdom:

Many people will, I know, object to this conclusion…. [It] seems very counterintuitive… and is very much at odds with what almost every policymaker and influential figure has been saying…. when I have tried laying out this argument to other economists, I have found that in general they recognize the point but argue that real-world complications mean that a sudden stop will nonetheless be contractionary even in countries with independent currencies and floating rates. Why? They offer a variety of reasons….

And Paul goes on:

The short-term/long-term interest rate distinction does not appear to offer any channel through which a nation with an independent currency can suffer a decline in output due to reduced foreign willingness to hold its debt….

Several commentators—for example, Rogoff (2013)—have suggested that a sudden stop of capital inflows provoked by concerns over sovereign debt would inevitably lead to a banking crisis…. [But] why, exactly… should [we] believe that a sudden stop leads to a banking crisis…. [It is] is only a problem for the banks if they have large liabilities denominated in foreign currency…. Inflation—and fear of inflation—is a potential channel through which sudden stops can end up being contractionary even for countries with independent currencies and domestic-currency debt…. Large foreign-currency debt can effectively undermine monetary independence, as can fears of depreciation-led inflation. However, the major nations with large debts but independent currencies don’t have large foreign-currency debt, and are currently quite remote from inflation pressure. So the crisis story remains very hard to tell.

I would say that the major nations with large debts don’t have large foreign-currency debt that we know of…