リカルド・カバレロミネアポリス連銀の機関紙「Region」のインタビューに登場しているEconomist's View経由)。その最後の方では現在のマクロ経済学に対する批判を繰り広げているので、以下に紹介してみる。

Region: At the end of last year, you published a rather biting critique of the way both academic and central bank researchers practice macroeconomics. You warned that what you called the “pretense-of-knowledge syndrome” is dangerous for both methodological and policy reasons.

Would you briefly review that critique and elaborate on what you consider a silver lining—that by seeking tools and policies that are robust to the “enormous uncertainty to which we are confined,” we can make some progress? Also, would you tell us how your colleagues have responded to your critique?

Caballero: There is an enormous selection bias in the reactions. I’ve mostly heard the positive ones, which have been plenty, but I’m sure I didn’t please everyone­—there are many polite people in our profession [laughter].

Region: It occurs to me that as head of the department at MIT, you have real influence in terms of how economics is taught here. Does it shape the way you teach and where you lead the department?

Caballero: Well, the assumption that a department head has that kind of power is quite a stretch [laughter]! Having said this, I’m about to teach a course in which I will, in the introduction, talk briefly about this methodological issue. But I still need to teach the basic models. That won’t change.

In fact, I think it is very important to clarify that I am not antimodel. On the contrary, the economy is so complex that there is little hope of understanding much without models. I just don’t want these models to acquire a life that is independent from the purpose they are ultimately designed to serve, which is to understand the functioning of real economies.

The critique part of the paper you refer to argued that the current core of macroeconomics has become so mesmerized with its own internal logic that it begins to confuse the precision it has achieved about its own world with the precision it has about the real one.

There is absolutely nothing wrong with building stylized structures as just one more tool to understand a piece of the complex problem. My problems with this start when these structures take on a life on their own, and researchers choose to “take the model seriously”—a statement that signals the time to leave a seminar, for it is always followed by a sequence of naïve and surreal claims.

The quantitative implications of this core approach, which are built on supposedly “micro-founded” calibrations of key parameters, are definitely on the surreal side. Take, for example, the preferred “micro-foundation” of the supply of capital in the workhorse models of the core approach. A key parameter to calibrate in these models is the intertemporal substitution elasticity of a representative agent, which is to be estimated from micro-data. A whole literature develops around this estimation, which narrows the parameter to certain values, which are then to be used and honored by anyone wanting to say something about “modern” macroeconomics.

This parameter may be a reasonable estimate for an individual agent facing a specific micro decision, but what does it have to do with the aggregate? What happened with the role of Chinese bureaucrats, Gulf autocrats and the like in the supply of capital? A typical answer is not to worry about it, because this is all “as if.” But then, why do we call this strategy “micro-foundation” rather than “reduced-form”?

My point is that by some strange herding process, the core of macroeconomics seems to transform things that may have been useful modeling short-cuts into a part of a new and artificial “reality.” And now suddenly everyone uses the same language, which in the next iteration gets confused with, and eventually replaces, reality. Along the way, this process of make-believe substitution raises our presumption of knowledge about the workings of a complex economy and increases the risks of a “pretense of knowledge” about which Hayek warned us in his Nobel Prize acceptance speech.

Region: We mistake the model for truth itself.

Caballero: Yes. It is much more convenient to talk about things we understand than about things we are struggling to understand. But at the end of the day, we’re supposed to explain the things that are hard to understand, so we are spinning the wheels to help us feel busy rather than making actual progress.

Region: What should be done to improve this state of affairs?

Caballero: I argue in the paper that there are lots of useful insights being produced in the periphery of macroeconomics, and that perhaps a key step is to embrace the complexity of the environment and what it does to economic agents and their decisions, as well as to our conclusions as researchers. I think the work on robust control by Hansen, Sargent and others is a step in the right direction, although it still assumes that policymakers know too much.

But a big part of my point is that no one really knows with any certainty what we need to do next, and hence we need to allow for much more freedom of exploration. We shouldn’t specialize so much in one particular class of models because we’re not sufficiently close to an absolute truth to do that. That’s the optimal thing to do when you’re very close to the global maximum, which we are not. We should be a lot more tolerant of alternative approaches and never forget our mission, which is to help understand an overwhelmingly complex reality, not to replace it with one that is more convenient to us as researchers.

Region: Thank you very much.

その批判について簡単に解説して頂けないでしょうか? また、あなたが希望の光と考えるもの、即ち、「我々がその制約下に置かれている多大な不確実性」に耐えうるツールと政策を追究することにより、何らかの進歩を成し遂げられる、という話をもっと詳しくご説明頂けないでしょうか? あと、あなたの批判に同僚の方々がどう反応したかも教えて頂けないでしょうか?



まあ、学部長がそれだけの力を持っているというのはちょっと過大評価のし過ぎですね!(笑) ただし、講義を受け持つ課程の導入部では、この方法論の問題を簡単に取り上げるつもりです。とは言え、基礎的なモデルは教えなくてはなりません。それはこれまでと変わりありません。

この変数は、個々の主体が特定のミクロの決断に直面した際の合理的な推定値になっているかもしれませんが、それがマクロの総量とどう関係するのでしょうか? 資本の供給において中国の官僚や湾岸諸国の独裁者などが果たす役割はどこへ行ったのでしょうか? その疑問に対する典型的な回答は、これは皆「仮定」の話なのだから気にするな、というものです。しかしそれならば、なぜこうした手法を「還元型」ではなく「ミクロ的基礎」と呼ぶのでしょうか?