RBC models — the art of missing the point completely

23 February, 2017 at 09:24 | Posted in Economics | 1 Comment

cgr0556l-jpgThe real business cycle program is part of the larger new classical macroeconomic research program. Proponents of these models often promote them as models that provide satisfactory microfoundations for macroeconomics … The claim for providing microfoundations is largely based on the fact that new classical models in general, and real business cycle models in particular, model the representative agent as solving a single dynamic optimization problem on behalf of all the consumers, workers, and firms in the economy. However, the claim that representative agent models are innately superior to other sorts of models is unfounded. There is no a priori reason to accord real business cycle models a presumption of accuracy because they look like they are based on microeconomics. Rather, there are several reasons to be theoretically skeptical of such models.

Most familiar to economists is the problem of the fallacy of composition … It is difficult to deny that what is true for an individual may not be true for a group, yet, representative agent models explicitly embody the fallacy of composition … By completely eliminating even the possibility of problems relating to coordination, representative agent models are inherently incapable of modeling such complexities.

The real business cycle model thus employs the formal mathematics of microeconomics, but applies it in a theoretically inappropriate circumstance: it provides the simulacrum of microfoundations, not the genuine article. It is analogous to modeling the behavior of a gas by a careful analysis of a single molecule in vacuo, or, of a crowd of people by an analysis of the actions of a single android. For some issues, such models may work well; for many others, they will miss the point completely.

James E.Hartley, Kevin D.Hoover and Kevin D.Salyer

RBC is one of the theories that has put macroeconomics on a path of intellectual regress for three decades now. And although there are many kinds of useless ‘post-real’economics held in high regard within mainstream economics establishment today, few — if any — are less deserved than real business cycle theory.

The future is not reducible to a known set of prospects. It is not like sitting at the roulette table and calculating what the future outcomes of spinning the wheel will be. So instead of — as RBC economists do — assuming calibration and rational expectations to be right, one ought to confront the hypothesis with the available evidence. It is not enough to construct models. Anyone can construct models. To be seriously interesting, models have to come with an aim. They have to have an intended use. If the intention of calibration and rational expectations  is to help us explain real economies, it has to be evaluated from that perspective. A model or hypothesis without a specific applicability is not really deserving our interest.

Without strong evidence all kinds of absurd claims and nonsense may pretend to be science. We have to demand more of a justification than rather watered-down versions of ‘anything goes’ when it comes to rationality postulates. If one proposes rational expectations one also has to support its underlying assumptions. None is given by RBC economists, which makes it rather puzzling how rational expectations has become the standard modeling assumption made in much of modern macroeconomics. Perhaps the reason is that economists often mistake mathematical beauty for truth.

In the hands of Lucas, Prescott and Sargent, rational expectations has been transformed from an – in principle – testable hypothesis to an irrefutable proposition. Believing in a set of irrefutable propositions may be comfortable – like religious convictions or ideological dogmas – but it is not  science.

So where does this all lead us? What is the trouble ahead for economics? Putting a sticky-price DSGE lipstick on the RBC pig sure won’t do. Neither will — as Paul Romer noticed  — just looking the other way and pretend it’s raining:

The trouble is not so much that macroeconomists say things that are inconsistent with the facts. The real trouble is that other economists do not care that the macroeconomists do not care about the facts. An indifferent tolerance of obvious error is even more corrosive to science than committed advocacy of error.

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1 Comment

  1. Professor, you use the BEST cartoons and illustrations with your posts. The one above is particularly good for this post.


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