政府の仕事には十分? 危機以降のマクロ経済学

昨日サイモン・レンールイスの掲載論文を紹介したOxford Review of Economic Policyの最新号には、クルーグマンの表題の論文(原題は「Good enough for government work? Macroeconomics since the crisis」)も掲載されている

The intellectual impact of the crisis just seems far more muted than the scale of crisis might have led one to expect. Why?
Well, I’m going to offer what I suspect will be a controversial answer: namely, macroeconomics hasn’t changed that much because it was, in two senses, what my father’s generation used to call ‘good enough for government work’. On one side, the basic models used by macroeconomists who either practise or comment frequently on policy have actually worked quite well, indeed remarkably well. On the other, the policy response to the crisis, while severely lacking in many ways, was sufficient to avert utter disaster, which in turn allowed the more inflexible members of our profession to ignore events in a way they couldn’t in past episodes.


Why hasn’t macroeconomics been transformed by (relatively) recent events in the way it was by events in the 1930s or the 1970s? Maybe the key point to remember is that such transformations are rare in economics, or indeed in any field. ‘Science advances one funeral at a time,’ quipped Max Planck: researchers rarely change their views much in the light of experience or evidence. The 1930s and the 1970s, in which senior economists changed their minds—e.g. Lionel Robbins converting to Keynesianism, were therefore exceptional.
What made them exceptional? Each case was marked by developments that were both clearly inconsistent with widely held views and sustained enough that they couldn’t be written off as aberrations. Lionel Robbins published The Great Depression, a very classical/Austrian interpretation that prescribed a return to the gold standard, in 1934. Would he have become a Keynesian if the Depression had ended by the mid-1930s? The widespread acceptance of the natural-rate hypothesis came more easily, because it played into the neoclassical mindset, but still might not have happened as thoroughly if stagflation had been restricted to a few years in the early 1970s.
マクロ経済学に1930年代や1970年代の出来事によって起きたような転換が(比較的)最近の出来事によって起きなかったのはなぜか? おそらく念頭に置いておくべき重要なポイントは、そうした転換は経済学のみならずどの分野でも稀だ、という点である。「科学は葬式ごとに進歩する」という警句をマックス・プランクは発した。経験や証拠に照らして研究者が見解を大きく変えるのは稀である。ライオネル・ロビンズがケインズ主義に転向したように年長の経済学者が考えを変えた1930年代や1970年代の出来事は、従って例外的なものである。
なぜそれらは例外的なものとなったのか? いずれのケースも、広く支持されていた見解と明確に矛盾し、かつ、逸脱として片付けられないほど長く続いた、という展開を特徴としていた。ライオネル・ロビンズは、1934年に、非常に古典派的かつオーストリア学派的な解釈に立つ「大恐慌」を出版し、金本位制への回帰を処方箋として打ち出した。大恐慌が1930年代半ばまでに終了していたら彼はケインジアンになっていただろうか? 自然失業率仮説はもっと簡単に広く受け入れられたが、それは新古典派的な考え方に訴求するものだったからである。しかしそれでも、スタグフレーションが1970年代初めの数年限りのものだったら、あれほど全面的に受け入れられることは無かったであろう。



Clever modellers pointed out that in the face of imperfect competition the aggregate costs of departures from perfectly rational price-setting could be much larger than the individual costs. As a result, small menu costs or a bit of bounded rationality could be consistent with widespread price and wage stickiness.
To be blunt again, however, in practice this insight served as an excuse rather than a basis for deep understanding. Sticky prices could be made respectable—just—allowing modellers to assume something like one-period-ahead price-setting, in turn letting models that were otherwise grounded in rationality and equilibrium produce something not too inconsistent with real-world observation. New Keynesian modelling thus acted as a kind of escape clause rather than a foundational building block.
But is that escape clause good enough to explain the failure of deflation to emerge despite multiple years of very high unemployment? Probably not. And yet we still lack a compelling alternative explanation, indeed any kind of big idea. At some level, wage and price behaviour in a depressed economy seems to be a subject for which our intellectual tools are badly fitted.
The good news is that if one simply assumed that prices and wages are sticky, appealing to the experience of the 1930s and Japan in the 1990s (which never experienced a true deflationary spiral), one did reasonably well on other fronts.
So my claim that basic macroeconomics worked very well after the crisis needs to be qualified by what looks like a big failure in our understanding of price dynamics—but this failure didn’t do too much damage in giving rise to bad advice, and hasn’t led to big new ideas because nobody seems to have good ideas to offer.
しかしその但し書きは、何年も非常に高い失業が続いているのにデフレーションが生じないことを説明するのに十分なものとなっているだろうか? おそらくなっていない。しかしながら我々は、それに代わる説得力のある説明を未だに欠いている。何らかの大きなアイディアが全く出ていないのだ。ある段階においては、不況経済における賃金と物価の振る舞いは、我々の知的道具が適していないテーマとなるように思われる。

*1:cf. ここ

*2:cf. ここ