First, there's Paul Romer's latest, "The Trouble With Macroeconomics". The title is an analogy to Lee Smolin's book "The Trouble With Physics". Romer basically says that macro (meaning business-cycle theory) has become like the critics' harshest depictions of string theory - a community of believers, dogmatically following the ideas of revered elders and ignoring the data. The elders he singles out are Bob Lucas, Ed Prescott, and Tom Sargent.
Romer says that it's obvious that monetary policy affects the real economy, because of the Volcker recessions in the early 80s, but that macro theorists have largely ignored this fact and continued to make models in which monetary policy is ineffectual. He says that modern DSGE models are no better than old pre-Lucas Critique simultaneous-equation models, because they still take lots of assumptions to identify the models, only now the assumptions are hidden instead of explicit. Romer points to distributional assumptions, calibration, and tight Bayesian priors as ways of hiding assumptions in modern DSGE models. He cites an interesting 2009 paper by Canova and Sala that tries to take DSGE model estimation seriously and finds (unsurprisingly) that identification is pretty difficult.
As a solution, Romer suggests chucking formal modeling entirely and going with more general, vague but flexible ideas about policy and the macroeconomy, supported by simple natural experiments and economic history.
Romer's harshest zinger (and we all love harsh zingers) is this:
In response to the observation that the shocks [in DSGE models] are imaginary, a standard defense invokes Milton Friedman’s (1953) methodological assertion from unnamed authority that "the more significant the theory, the more unrealistic the assumptions (p.14)." More recently, "all models are false" seems to have become the universal hand-wave for dismissing any fact that does not conform to the model that is the current favorite.
The noncommittal relationship with the truth revealed by these methodological evasions...goes so far beyond post-modern irony that it deserves its own label. I suggest "post-real."
Ouch. He also calls various typical DSGE model elements names like "phlogiston", "aether", and "caloric". Fun stuff. (Though I do think he's too harsh on string theory, which often is just a kind of math that physicists do to keep themselves busy, and has no danger of hurting anyone, unlike macro theory.)
Meanwhile, a few weeks earlier, Narayana Kocherlakota wrote a post called "On the Puzzling Prevalence of Puzzles". The basic point was that since macro data is fairly sparse, macroeconomists should have lots of competing models that all do an equally good job of matching the data. But instead, macroeconomists pick a single model they like, and if data fails to fit the model they call it a "puzzle". He writes:
To an outsider or newcomer, macroeconomics would seem like a field that is haunted by its lack of data...In the absence of that data, it would seem like we would be hard put to distinguish among a host of theories...[I]t would seem like macroeconomists should be plagued by underidentification...
But, in fact, expert macroeconomists know that the field is actually plagued by failures to fit the data – that is, by overidentification.
Why is the novice so wrong? The answer is the role of a priori restrictions in macroeconomic theory...
The mistake that the novice made is to think that the macroeconomist would rely on data alone to build up his/her theory or model. The expert knows how to build up theory from a priori restrictions that are accepted by a large number of scholars...[I]t’s a little disturbing how little empirical work underlies some of those agreed-upon theory-driven restrictions – see p. 711 of Lucas (JMCB, 1980) for a highly influential example of what I mean.
In fact, Kocherlakota and Romer are complaining about much the same thing: the overuse of unrealistic assumptions. Basically, they say that macroeconomists, as a group, have gotten into the habit of assuming stuff that just isn't true. In fact, this is what the Canova and Sala paper says too, in a much more technical and polite way:
Observational equivalence, partial and weak identification problems are widespread and typically produced by an ill-behaved mapping between the structural parameters and the coefficients of the solution.
That just means that the model elements aren't actually real things.
(This critique resonates with me. From day 1, the thing that always annoyed me about macro was how people made excuses for assumptions that were either unverifiable or just flatly contradictory to micro data. The usual excuse was the "pool player analogy" - the idea that the pieces of a model don't have to match micro data as long as the resulting model matches macro data. I'm not sure that's how Milton Friedman wanted his metaphor to be used, but that seems to be the way it does get used. And when the models didn't match macro data either, the excuse was "all models are wrong," which really just seems to be a way of saying "the modeler gets to choose which macro facts are used to validate his theory". It seemed that to a large extent, macro modelers were just allowed to do whatever they wanted, as long as their papers won some kind of behind-the-scenes popularity contest. But I digress.)
So what seems to unite the new heavyweight macro critics, besides a lingering annoyance with Bob Lucas and his associates, is an emphasis on realism. Basically, these people are challenging the idea, very common in econ theory, that models shouldn't worry about being realistic. (Paul Pfleiderer is another economist who has recently made a similar complaint, though not in the context of macro.) They're not saying that economists need 100% perfect realism - that's the kind of thing you only get in physics, if anywhere. As Paul Krugman and Dani Rodrik have emphasized, even the people advocating for more realism acknowledge that there's some ideal middle ground. But if Romer, Kocherlakota, etc. are to be believed, macroeconomists aren't currently close to that optimal interior solution.
from Noahpinion http://ift.tt/2cfhu8W