Does God really share the same model as Sargent?

22 Oct, 2011 at 19:54 | Posted in Economics, Theory of Science & Methodology | Comments Off on Does God really share the same model as Sargent?

Professor John Kay has a marvelous article on the latest Nobel Prize in Economics – awarded to Christopher Sims and Thomas Sargent – in last week’s Financial Times. Kay writes: 

As the Nobel committee observes, “economic behaviour depends on expectations about the future and economists must consider how such expectations are formed”. In a brilliant linguistic coup, Prof Sargent and colleagues appropriated the term “rational expectations” for their answer. Suppose the economic world evolves according to some predetermined model, in which uncertainties are “known unknowns” that can be described by probability distributions. Then economists could gradually deduce the properties of this model, and businesses and individuals would naturally form expectations in that light. If they did not, they would be missing obvious opportunities for advantage.

This approach, which postulates a universal explanation into which economists have privileged insight, was as influential as it was superficially attractive. But a scientific idea is not seminal because it influences the research agenda of PhD students. An important scientific advance yields conclusions that differ from those derived from other theories, and establishes that these divergent conclusions are supported by observation. Yet as Prof Sargent disarmingly observed, “such empirical tests were rejecting too many good models” in the programme he had established with fellow Nobel laureates Bob Lucas and Ed Prescott. In their world, the validity of a theory is demonstrated if, after the event, and often with torturing of data and ad hoc adjustments that are usually called “imperfections”, it can be reconciled with already known facts – “calibrated”. Since almost everything can be “explained” in this way, the theory is indeed universal; no other approach is necessary, or even admissible. Asked “do you think that differences among people’s models are important aspects of macroeconomic policy debates”, Prof Sargent replied: “The fact is you simply cannot talk about their differences within the typical rational expectations model. There is a communism of models. All agents within the model, the econometricians, and God share the same model.”

Rational expectations consequently fail for the same reason communism failed – the arrogance and ignorance of the monopolist. In their critique of rational expectations, Roman Frydman and Michael Goldberg employ Hayek’s critique of planning; the market economy, unlike communism, can mediate different perceptions of the world, bringing together knowledge whose totality is not held by anyone. God did not vouchsafe his model to us, mortals see the present imperfectly and the future dimly, and use many different models. Some agents made profits, some losses, and the financial crisis of 2007-08 decided which was which. Only Prof Sargent’s econometricians were wedded to a single model and could, as usual, explain the crisis only after it had occurred. For them, the crisis was a random shock, but the occasion for a Nobel prize.

One might perhaps find it odd to juxtapose God and people, but I think Leonard Rapping – himself a former rational expectationist  – was on the right track (Arjo Klamer, The New Classical Macroeconomics 1984, p 234):

Frankly, I do not think that the rational expectations theorists are in the real world. Their approach is much to abstract.

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