Archive for the 'New Classical macroeconomics' Category

Rational Expectations, or, The Road to Incoherence

J. W. Mason left a very nice comment on my recent post about Paul Romer’s now-famous essay on macroeconomics, a comment now embedded in his interesting and insightful blog post on the Romer essay. As a wrote in my reply to Mason’s comment, I really liked the way he framed his point about rational expectations and intertemporal equilibrium. Sometimes when you see a familiar idea expressed in a particular way, the novelty of the expression, even though it’s not substantively different from other ways of expressing the idea, triggers a new insight. And that’s what I think happened in my own mind as I read Mason’s comment. Here’s what he wrote:

David Glasner’s interesting comment on Romer makes in passing a point that’s bugged me for years — that you can’t talk about transitions from one intertemporal equilibrium to another, there’s only the one. Or equivalently, you can’t have a model with rational expectations and then talk about what happens if there’s a “shock.” To say there is a shock in one period, is just to say that expectations in the previous period were wrong. Glasner:

the Lucas Critique applies even to micro-founded models, those models being strictly valid only in equilibrium settings and being unable to predict the adjustment of economies in the transition between equilibrium states. All models are subject to the Lucas Critique.

So the further point that I would make, after reading Mason’s comment, is just this. For an intertemporal equilibrium to exist, there must be a complete set of markets for all future periods and contingent states of the world, or, alternatively, there must be correct expectations shared by all agents about all future prices and the probability that each contingent future state of the world will be realized. By the way, If you think about it for a moment, the notion that probabilities can be assigned to every contingent future state of the world is mind-bogglingly unrealistic, because the number of contingent states must rapidly become uncountable, because every single contingency itself gives rise to further potential contingencies, and so on and on and on. But forget about that little complication. What intertemporal equilibrium requires is that all expectations of all individuals be in agreement – or at least not be inconsistent, some agents possibly having an incomplete set of expectations about future prices and future states of the world. If individuals differ in their expectations, so that their planned future purchases and sales are based on what they expect future prices to be when the time comes for those transactions to be carried out, then individuals will not be able to execute their plans as intended when at least one of them finds that actual prices are different from what they had been expected to be.

What this means is that expectations can be rational only when everyone has identical expectations. If people have divergent expectations, then the expectations of at least some people will necessarily be disappointed — the expectations of both people with differing expectations cannot be simultaneously realized — and those individuals whose expectations have been disappointed will have to revise their plans. But that means that the expectations of those people who were correct were also not rational, because the prices that they expected were not equilibrium prices. So unless all agents have the same expectations about the future, the expectations of no one are rational. Rational expectations are a fixed point, and that fixed point cannot be attained unless everyone shares those expectations.

Beyond that little problem, Mason raises the further problem that, in a rational-expectations equilibrium, it makes no sense to speak of a shock, because the only possible meaning of “shock” in the context of a full intertemporal (aka rational-expectations) equilibrium is a failure of expectations to be realized. But if expectations are not realized, expectations were not rational. So the whole New Classical modeling strategy of identifying shocks  to a system in rational-expectations equilibrium, and “predicting” the responses to these shocks as if they had been anticipated is self-contradictory and incoherent.

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Paul Romer on Modern Macroeconomics, Or, the “All Models Are False” Dodge

Paul Romer has been engaged for some time in a worthy campaign against the travesty of modern macroeconomics. A little over a year ago I commented favorably about Romer’s takedown of Robert Lucas, but I also defended George Stigler against what I thought was an unfair attempt by Romer to identify George Stigler as an inspiration and role model for Lucas’s transgressions. Now just a week ago, a paper based on Romer’s Commons Memorial Lecture to the Omicron Delta Epsilon Society, has become just about the hottest item in the econ-blogosophere, even drawing the attention of Daniel Drezner in the Washington Post.

I have already written critically about modern macroeconomics in my five years of blogging, and here are some links to previous posts (link, link, link, link). It’s good to see that Romer is continuing to voice his criticisms, and that they are gaining a lot of attention. But the macroeconomic hierarchy is used to criticism, and has its standard responses to criticism, which are being dutifully deployed by defenders of the powers that be.

Romer’s most effective rhetorical strategy is to point out that the RBC core of modern DSGE models posit unobservable taste and technology shocks to account for fluctuations in the economic time series, but that these taste and technology shocks are themselves simply inferred from the fluctuations in the times-series data, so that the entire structure of modern macroeconometrics is little more than an elaborate and sophisticated exercise in question-begging.

In this post, I just want to highlight one of the favorite catch-phrases of modern macroeconomics which serves as a kind of default excuse and self-justification for the rampant empirical failures of modern macroeconomics (documented by Lipsey and Carlaw as I showed in this post). When confronted by evidence that the predictions of their models are wrong, the standard and almost comically self-confident response of the modern macroeconomists is: All models are false. By which the modern macroeconomists apparently mean something like: “And if they are all false anyway, you can’t hold us accountable, because any model can be proven wrong. What really matters is that our models, being microfounded, are not subject to the Lucas Critique, and since all other models than ours are not micro-founded, and, therefore, being subject to the Lucas Critique, they are simply unworthy of consideration. This is what I have called methodological arrogance. That response is simply not true, because the Lucas Critique applies even to micro-founded models, those models being strictly valid only in equilibrium settings and being unable to predict the adjustment of economies in the transition between equilibrium states. All models are subject to the Lucas Critique.

Here is Romer’s take:

In response to the observation that the shocks 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.

Friedman’s methodological assertion would have been correct had Friedman substituted “simple” for “unrealistic.” Sometimes simplifications are unrealistic, but they don’t have to be. A simplification is a generalization of something complicated. By simplifying, we can transform a problem that had been too complex to handle into a problem more easily analyzed. But such simplifications aren’t necessarily unrealistic. To say that all models are false is simply a dodge to avoid having to account for failure. The excuse of course is that all those other models are subject to the Lucas Critique, so my model wins. But your model is subject to the Lucas Critique even though you claim it’s not, so even according to the rules you have arbitrarily laid down, you don’t win.

So I was just curious about where the little phrase “all models are false” came from. I was expecting that Karl Popper might have said it, in which case to use the phrase as a defense mechanism against empirical refutation would have been a particularly fraudulent tactic, because it would have been a perversion of Popper’s methodological stance, which was to force our theoretical constructs to face up to, not to insulate it from, empirical testing. But when I googled “all theories are false” what I found was not Popper, but the British statistician, G. E. P. Box who wrote in his paper “Science and Statistics” based on his R. A. Fisher Memorial Lecture to the American Statistical Association: “All models are wrong.” Here’s the exact quote:

Since all models are wrong the scientist cannot obtain a “correct” one by excessive elaboration. On the contrary following William of Occam he should seek an economical description of natural phenomena. Just as the ability to devise simple but evocative models is the signature of the great scientist so overelaboration and overparameterization is often the mark of mediocrity.

Since all models are wrong the scientist must be alert to what is importantly wrong. It is inappropriate to be concerned about mice when there are tigers abroad. Pure mathematics is concerned with propositions like “given that A is true, does B necessarily follow?” Since the statement is a conditional one, it has nothing whatsoever to do with the truth of A nor of the consequences B in relation to real life. The pure mathematician, acting in that capacity, need not, and perhaps should not, have any contact with practical matters at all.

In applying mathematics to subjects such as physics or statistics we make tentative assumptions about the real world which we know are false but which we believe may be useful nonetheless. The physicist knows that particles have mass and yet certain results, approximating what really happens, may be derived from the assumption that they do not. Equally, the statistician knows, for example, that in nature there never was a normal distribution, there never was a straight line, yet with normal and linear assumptions, known to be false, he can often derive results which match, to a useful approximation, those found in the real world. It follows that, although rigorous derivation of logical consequences is of great importance to statistics, such derivations are necessarily encapsulated in the knowledge that premise, and hence consequence, do not describe natural truth.

It follows that we cannot know that any statistical technique we develop is useful unless we use it. Major advances in science and in the science of statistics in particular, usually occur, therefore, as the result of the theory-practice iteration.

One of the most annoying conceits of modern macroeconomists is the constant self-congratulatory references to themselves as scientists because of their ostentatious use of axiomatic reasoning, formal proofs, and higher mathematical techniques. The tiresome self-congratulation might get toned down ever so slightly if they bothered to read and take to heart Box’s lecture.

There Is No Intertemporal Budget Constraint

Last week Nick Rowe posted a link to a just published article in a special issue of the Review of Keynesian Economics commemorating the 80th anniversary of the General Theory. Nick’s article discusses the confusion in the General Theory between saving and hoarding, and Nick invited readers to weigh in with comments about his article. The ROKE issue also features an article by Simon Wren-Lewis explaining the eclipse of Keynesian theory as a result of the New Classical Counter-Revolution, correctly identified by Wren-Lewis as a revolution inspired not by empirical success but by a methodological obsession with reductive micro-foundationalism. While deploring the New Classical methodological authoritarianism, Wren-Lewis takes solace from the ability of New Keynesians to survive under the New Classical methodological regime, salvaging a role for activist counter-cyclical policy by, in effect, negotiating a safe haven for the sticky-price assumption despite its shaky methodological credentials. The methodological fiction that sticky prices qualify as micro-founded allowed New Keynesianism to survive despite the ascendancy of micro-foundationalist methodology, thereby enabling the core Keynesian policy message to survive.

I mention the Wren-Lewis article in this context because of an exchange between two of the commenters on Nick’s article: the presumably pseudonymous Avon Barksdale and blogger Jason Smith about microfoundations and Keynesian economics. Avon began by chastising Nick for wasting time discussing Keynes’s 80-year old ideas, something Avon thinks would never happen in a discussion about a true science like physics, the 100-year-old ideas of Einstein being of no interest except insofar as they have been incorporated into the theoretical corpus of modern physics. Of course, this is simply vulgar scientism, as if the only legitimate way to do economics is to mimic how physicists do physics. This methodological scolding is typically charming New Classical arrogance. Sort of reminds one of how Friedrich Engels described Marxian theory as scientific socialism. I mean who, other than a religious fanatic, would be stupid enough to argue with the assertions of science?

Avon continues with a quotation from David Levine, a fine economist who has done a lot of good work, but who is also enthralled by the New Classical methodology. Avon’s scientism provoked the following comment from Jason Smith, a Ph. D. in physics with a deep interest in and understanding of economics.

You quote from Levine: “Keynesianism as argued by people such as Paul Krugman and Brad DeLong is a theory without people either rational or irrational”

This is false. The L in ISLM means liquidity preference and e.g. here …

http://krugman.blogs.nytimes.com/2013/11/18/the-new-keynesian-case-for-fiscal-policy-wonkish/

… Krugman mentions an Euler equation. The Euler equation essentially says that an agent must be indifferent between consuming one more unit today on the one hand and saving that unit and consuming in the future on the other if utility is maximized.

So there are agents in both formulations preferring one state of the world relative to others.

Avon replied:

Jason,

“This is false. The L in ISLM means liquidity preference and e.g. here”

I know what ISLM is. It’s not recursive so it really doesn’t have people in it. The dynamics are not set by any micro-foundation. If you’d like to see models with people in them, try Ljungqvist and Sargent, Recursive Macroeconomic Theory.

To which Jason retorted:

Avon,

So the definition of “people” is restricted to agents making multi-period optimizations over time, solving a dynamic programming problem?

Well then any such theory is obviously wrong because people don’t behave that way. For example, humans don’t optimize the dictator game. How can you add up optimizing agents and get a result that is true for non-optimizing agents … coincident with the details of the optimizing agents mattering.

Your microfoundation requirement is like saying the ideal gas law doesn’t have any atoms in it. And it doesn’t! It is an aggregate property of individual “agents” that don’t have properties like temperature or pressure (or even volume in a meaningful sense). Atoms optimize entropy, but not out of any preferences.

So how do you know for a fact that macro properties like inflation or interest rates are directly related to agent optimizations? Maybe inflation is like temperature — it doesn’t exist for individuals and is only a property of economics in aggregate.

These questions are not answered definitively, and they’d have to be to enforce a requirement for microfoundations … or a particular way of solving the problem.

Are quarks important to nuclear physics? Not really — it’s all pions and nucleons. Emergent degrees of freedom. Sure, you can calculate pion scattering from QCD lattice calculations (quark and gluon DoF), but it doesn’t give an empirically better result than chiral perturbation theory (pion DoF) that ignores the microfoundations (QCD).

Assuming quarks are required to solve nuclear physics problems would have been a giant step backwards.

To which Avon rejoined:

Jason

The microfoundation of nuclear physics and quarks is quantum mechanics and quantum field theory. How the degrees of freedom reorganize under the renormalization group flow, what effective field theory results is an empirical question. Keynesian economics is worse tha[n] useless. It’s wrong empirically, it has no theoretical foundation, it has no laws. It has no microfoundation. No serious grad school has taught Keynesian economics in nearly 40 years.

To which Jason answered:

Avon,

RG flow is irrelevant to chiral perturbation theory which is based on the approximate chiral symmetry of QCD. And chiral perturbation theory could exist without QCD as the “microfoundation”.

Quantum field theory is not a ‘microfoundation’, but rather a framework for building theories that may or may not have microfoundations. As Weinberg (1979) said:

” … quantum field theory itself has no content beyond analyticity, unitarity,
cluster decomposition, and symmetry.”

If I put together an NJL model, there is no requirement that the scalar field condensate be composed of quark-antiquark pairs. In fact, the basic idea was used for Cooper pairs as a model of superconductivity. Same macro theory; different microfoundations. And that is a general problem with microfoundations — different microfoundations can lead to the same macro theory, so which one is right?

And the IS-LM model is actually pretty empirically accurate (for economics):

http://informationtransfereconomics.blogspot.com/2014/03/the-islm-model-again.html

To which Avon responded:

First, ISLM analysis does not hold empirically. It just doesn’t work. That’s why we ended up with the macro revolution of the 70s and 80s. Keynesian economics ignores intertemporal budget constraints, it violates Ricardian equivalence. It’s just not the way the world works. People might not solve dynamic programs to set their consumption path, but at least these models include a future which people plan over. These models work far better than Keynesian ISLM reasoning.

As for chiral perturbation theory and the approximate chiral symmetries of QCD, I am not making the case that NJL models requires QCD. NJL is an effective field theory so it comes from something else. That something else happens to be QCD. It could have been something else, that’s an empirical question. The microfoundation I’m talking about with theories like NJL is QFT and the symmetries of the vacuum, not the short distance physics that might be responsible for it. The microfoundation here is about the basic laws, the principles.

ISLM and Keynesian economics has none of this. There is no principle. The microfoundation of modern macro is not about increasing the degrees of freedom to model every person in the economy on some short distance scale, it is about building the basic principles from consistent economic laws that we find in microeconomics.

Well, I totally agree that IS-LM is a flawed macroeconomic model, and, in its original form, it was borderline-incoherent, being a single-period model with an interest rate, a concept without meaning except as an intertemporal price relationship. These deficiencies of IS-LM became obvious in the 1970s, so the model was extended to include a future period, with an expected future price level, making it possible to speak meaningfully about real and nominal interest rates, inflation and an equilibrium rate of spending. So the failure of IS-LM to explain stagflation, cited by Avon as the justification for rejecting IS-LM in favor of New Classical macro, was not that hard to fix, at least enough to make it serviceable. And comparisons of the empirical success of augmented IS-LM and the New Classical models have shown that IS-LM models consistently outperform New Classical models.

What Avon fails to see is that the microfoundations that he considers essential for macroeconomics are themselves derived from the assumption that the economy is operating in macroeconomic equilibrium. Thus, insisting on microfoundations – at least in the formalist sense that Avon and New Classical macroeconomists understand the term – does not provide a foundation for macroeconomics; it is just question begging aka circular reasoning or petitio principia.

The circularity is obvious from even a cursory reading of Samuelson’s Foundations of Economic Analysis, Robert Lucas’s model for doing economics. What Samuelson called meaningful theorems – thereby betraying his misguided acceptance of the now discredited logical positivist dogma that only potentially empirically verifiable statements have meaning – are derived using the comparative-statics method, which involves finding the sign of the derivative of an endogenous economic variable with respect to a change in some parameter. But the comparative-statics method is premised on the assumption that before and after the parameter change the system is in full equilibrium or at an optimum, and that the equilibrium, if not unique, is at least locally stable and the parameter change is sufficiently small not to displace the system so far that it does not revert back to a new equilibrium close to the original one. So the microeconomic laws invoked by Avon are valid only in the neighborhood of a stable equilibrium, and the macroeconomics that Avon’s New Classical mentors have imposed on the economics profession is a macroeconomics that, by methodological fiat, is operative only in the neighborhood of a locally stable equilibrium.

Avon dismisses Keynesian economics because it ignores intertemporal budget constraints. But the intertemporal budget constraint doesn’t exist in any objective sense. Certainly macroeconomics has to take into account intertemporal choice, but the idea of an intertemporal budget constraint analogous to the microeconomic budget constraint underlying the basic theory of consumer choice is totally misguided. In the static theory of consumer choice, the consumer has a given resource endowment and known prices at which consumers can transact at will, so the utility-maximizing vector of purchases and sales can be determined as the solution of a constrained-maximization problem.

In the intertemporal context, consumers have a given resource endowment, but prices are not known. So consumers have to make current transactions based on their expectations about future prices and a variety of other circumstances about which consumers can only guess. Their budget constraints are thus not real but totally conjectural based on their expectations of future prices. The optimizing Euler equations are therefore entirely conjectural as well, and subject to continual revision in response to changing expectations. The idea that the microeconomic theory of consumer choice is straightforwardly applicable to the intertemporal choice problem in a setting in which consumers don’t know what future prices will be and agents’ expectations of future prices are a) likely to be very different from each other and thus b) likely to be different from their ultimate realizations is a huge stretch. The intertemporal budget constraint has a completely different role in macroeconomics from the role it has in microeconomics.

If I expect that the demand for my services will be such that my disposable income next year would be $500k, my consumption choices would be very different from what they would have been if I were expecting a disposable income of $100k next year. If I expect a disposable income of $500k next year, and it turns out that next year’s income is only $100k, I may find myself in considerable difficulty, because my planned expenditure and the future payments I have obligated myself to make may exceed my disposable income or my capacity to borrow. So if there are a lot of people who overestimate their future incomes, the repercussions of their over-optimism may reverberate throughout the economy, leading to bankruptcies and unemployment and other bad stuff.

A large enough initial shock of mistaken expectations can become self-amplifying, at least for a time, possibly resembling the way a large initial displacement of water can generate a tsunami. A financial crisis, which is hard to model as an equilibrium phenomenon, may rather be an emergent phenomenon with microeconomic sources, but whose propagation can’t be described in microeconomic terms. New Classical macroeconomics simply excludes such possibilities on methodological grounds by imposing a rational-expectations general-equilibrium structure on all macroeconomic models.

This is not to say that the rational expectations assumption does not have a useful analytical role in macroeconomics. But the most interesting and most important problems in macroeconomics arise when the rational expectations assumption does not hold, because it is when individual expectations are very different and very unstable – say, like now, for instance — that macroeconomies become vulnerable to really scary instability.

Simon Wren-Lewis makes a similar point in his paper in the Review of Keynesian Economics.

Much discussion of current divisions within macroeconomics focuses on the ‘saltwater/freshwater’ divide. This understates the importance of the New Classical Counter Revolution (hereafter NCCR). It may be more helpful to think about the NCCR as involving two strands. The one most commonly talked about involves Keynesian monetary and fiscal policy. That is of course very important, and plays a role in the policy reaction to the recent Great Recession. However I want to suggest that in some ways the second strand, which was methodological, is more important. The NCCR helped completely change the way academic macroeconomics is done.

Before the NCCR, macroeconomics was an intensely empirical discipline: something made possible by the developments in statistics and econometrics inspired by The General Theory. After the NCCR and its emphasis on microfoundations, it became much more deductive. As Hoover (2001, p. 72) writes, ‘[t]he conviction that macroeconomics must possess microfoundations has changed the face of the discipline in the last quarter century’. In terms of this second strand, the NCCR was triumphant and remains largely unchallenged within mainstream academic macroeconomics.

Perhaps I will have some more to say about Wren-Lewis’s article in a future post. And perhaps also about Nick Rowe’s article.

HT: Tom Brown

Update (02/11/16):

On his blog Jason Smith provides some further commentary on his exchange with Avon on Nick Rowe’s blog, explaining at greater length how irrelevant microfoundations are to doing real empirically relevant physics. He also expands on and puts into a broader meta-theoretical context my point about the extremely narrow range of applicability of the rational-expectations equilibrium assumptions of New Classical macroeconomics.

David Glasner found a back-and-forth between me and a commenter (with the pseudonym “Avon Barksdale” after [a] character on The Wire who [didn’t end] up taking an economics class [per Tom below]) on Nick Rowe’s blog who expressed the (widely held) view that the only scientific way to proceed in economics is with rigorous microfoundations. “Avon” held physics up as a purported shining example of this approach.
I couldn’t let it go: even physics isn’t that reductionist. I gave several examples of cases where the microfoundations were actually known, but not used to figure things out: thermodynamics, nuclear physics. Even modern physics is supposedly built on string theory. However physicists do not require every pion scattering amplitude be calculated from QCD. Some people do do so-called lattice calculations. But many resort to the “effective” chiral perturbation theory. In a sense, that was what my thesis was about — an effective theory that bridges the gap between lattice QCD and chiral perturbation theory. That effective theory even gave up on one of the basic principles of QCD — confinement. It would be like an economist giving up opportunity cost (a basic principle of the micro theory). But no physicist ever said to me “your model is flawed because it doesn’t have true microfoundations”. That’s because the kind of hard core reductionism that surrounds the microfoundations paradigm doesn’t exist in physics — the most hard core reductionist natural science!
In his post, Glasner repeated something that he had before and — probably because it was in the context of a bunch of quotes about physics — I thought of another analogy.

Glasner says:

But the comparative-statics method is premised on the assumption that before and after the parameter change the system is in full equilibrium or at an optimum, and that the equilibrium, if not unique, is at least locally stable and the parameter change is sufficiently small not to displace the system so far that it does not revert back to a new equilibrium close to the original one. So the microeconomic laws invoked by Avon are valid only in the neighborhood of a stable equilibrium, and the macroeconomics that Avon’s New Classical mentors have imposed on the economics profession is a macroeconomics that, by methodological fiat, is operative only in the neighborhood of a locally stable equilibrium.

 

This hits on a basic principle of physics: any theory radically simplifies near an equilibrium.

Go to Jason’s blog to read the rest of his important and insightful post.

Representative Agents, Homunculi and Faith-Based Macroeconomics

After my previous post comparing the neoclassical synthesis in its various versions to the mind-body problem, there was an interesting Twitter exchange between Steve Randy Waldman and David Andolfatto in which Andolfatto queried whether Waldman and I are aware that there are representative-agent models in which the equilibrium is not Pareto-optimal. Andalfatto raised an interesting point, but what I found interesting about it might be different from what Andalfatto was trying to show, which, I am guessing, was that a representative-agent modeling strategy doesn’t necessarily commit the theorist to the conclusion that the world is optimal and that the solutions of the model can never be improved upon by a monetary/fiscal-policy intervention. I concede the point. It is well-known I think that, given the appropriate assumptions, a general-equilibrium model can have a sub-optimal solution. Given those assumptions, the corresponding representative-agent will also choose a sub-optimal solution. So I think I get that, but perhaps there’s a more subtle point  that I’m missing. If so, please set me straight.

But what I was trying to argue was not that representative-agent models are necessarily optimal, but that representative-agent models suffer from an inherent, and, in my view, fatal, flaw: they can’t explain any real macroeconomic phenomenon, because a macroeconomic phenomenon has to encompass something more than the decision of a single agent, even an omniscient central planner. At best, the representative agent is just a device for solving an otherwise intractable general-equilibrium model, which is how I think Lucas originally justified the assumption.

Yet just because a general-equilibrium model can be formulated so that it can be solved as the solution of an optimizing agent does not explain the economic mechanism or process that generates the solution. The mathematical solution of a model does not necessarily provide any insight into the adjustment process or mechanism by which the solution actually is, or could be, achieved in the real world. Your ability to find a solution for a mathematical problem does not mean that you understand the real-world mechanism to which the solution of your model corresponds. The correspondence between your model may be a strictly mathematical correspondence which may not really be in any way descriptive of how any real-world mechanism or process actually operates.

Here’s an example of what I am talking about. Consider a traffic-flow model explaining how congestion affects vehicle speed and the flow of traffic. It seems obvious that traffic congestion is caused by interactions between the different vehicles traversing a thoroughfare, just as it seems obvious that market exchange arises as the result of interactions between the different agents seeking to advance their own interests. OK, can you imagine building a useful traffic-flow model based on solving for the optimal plan of a representative vehicle?

I don’t think so. Once you frame the model in terms of a representative vehicle, you have abstracted from the phenomenon to be explained. The entire exercise would be pointless – unless, that is, you assumed that interactions between vehicles are so minimal that they can be ignored. But then why would you be interested in congestion effects? If you want to claim that your model has any relevance to the effect of congestion on traffic flow, you can’t base the claim on an assumption that there is no congestion.

Or to take another example, suppose you want to explain the phenomenon that, at sporting events, all, or almost all, the spectators sit in their seats but occasionally get up simultaneously from their seats to watch the play on the field or court. Would anyone ever think that an explanation in terms of a representative spectator could explain that phenomenon?

In just the same way, a representative-agent macroeconomic model necessarily abstracts from the interactions between actual agents. Obviously, by abstracting from the interactions, the model can’t demonstrate that there are no interactions between agents in the real world or that their interactions are too insignificant to matter. I would be shocked if anyone really believed that the interactions between agents are unimportant, much less, negligible; nor have I seen an argument that interactions between agents are unimportant, the concept of network effects, to give just one example, being an important topic in microeconomics.

It’s no answer to say that all the interactions are accounted for within the general-equilibrium model. That is just a form of question-begging. The representative agent is being assumed because without him the problem of finding a general-equilibrium solution of the model is very difficult or intractable. Taking into account interactions makes the model too complicated to work with analytically, so it is much easier — but still hard enough to allow the theorist to perform some fancy mathematical techniques — to ignore those pesky interactions. On top of that, the process by which the real world arrives at outcomes to which a general-equilibrium model supposedly bears at least some vague resemblance can’t even be described by conventional modeling techniques.

The modeling approach seems like that of a neuroscientist saying that, because he could simulate the functions, electrical impulses, chemical reactions, and neural connections in the brain – which he can’t do and isn’t even close to doing, even though a neuroscientist’s understanding of the brain far surpasses any economist’s understanding of the economy – he can explain consciousness. Simulating the operation of a brain would not explain consciousness, because the computer on which the neuroscientist performed the simulation would not become conscious in the course of the simulation.

Many neuroscientists and other materialists like to claim that consciousness is not real, that it’s just an epiphenomenon. But we all have the subjective experience of consciousness, so whatever it is that someone wants to call it, consciousness — indeed the entire world of mental phenomena denoted by that term — remains an unexplained phenomenon, a phenomenon that can only be dismissed as unreal on the basis of a metaphysical dogma that denies the existence of anything that can’t be explained as the result of material and physical causes.

I call that metaphysical belief a dogma not because it’s false — I have no way of proving that it’s false — but because materialism is just as much a metaphysical belief as deism or monotheism. It graduates from belief to dogma when people assert not only that the belief is true but that there’s something wrong with you if you are unwilling to believe it as well. The most that I would say against the belief in materialism is that I can’t understand how it could possibly be true. But I admit that there are a lot of things that I just don’t understand, and I will even admit to believing in some of those things.

New Classical macroeconomists, like, say, Robert Lucas and, perhaps, Thomas Sargent, like to claim that unless a macroeconomic model is microfounded — by which they mean derived from an explicit intertemporal optimization exercise typically involving a representative agent or possibly a small number of different representative agents — it’s not an economic model, because the model, being vulnerable to the Lucas critique, is theoretically superficial and vacuous. But only models of intertemporal equilibrium — a set of one or more mutually consistent optimal plans — are immune to the Lucas critique, so insisting on immunity to the Lucas critique as a prerequisite for a macroeconomic model is a guarantee of failure if your aim to explain anything other than an intertemporal equilibrium.

Unless, that is, you believe that real world is in fact the realization of a general equilibrium model, which is what real-business-cycle theorists, like Edward Prescott, at least claim to believe. Like materialist believers that all mental states are epiphenomenous, and that consciousness is an (unexplained) illusion, real-business-cycle theorists purport to deny that there is such a thing as a disequilibrium phenomenon, the so-called business cycle, in their view, being nothing but a manifestation of the intertemporal-equilibrium adjustment of an economy to random (unexplained) productivity shocks. According to real-business-cycle theorists, such characteristic phenomena of business cycles as surprise, regret, disappointed expectations, abandoned and failed plans, the inability to find work at wages comparable to wages that other similar workers are being paid are not real phenomena; they are (unexplained) illusions and misnomers. The real-business-cycle theorists don’t just fail to construct macroeconomic models; they deny the very existence of macroeconomics, just as strict materialists deny the existence of consciousness.

What is so preposterous about the New-Classical/real-business-cycle methodological position is not the belief that the business cycle can somehow be modeled as a purely equilibrium phenomenon, implausible as that idea seems, but the insistence that only micro-founded business-cycle models are methodologically acceptable. It is one thing to believe that ultimately macroeconomics and business-cycle theory will be reduced to the analysis of individual agents and their interactions. But current micro-founded models can’t provide explanations for what many of us think are basic features of macroeconomic and business-cycle phenomena. If non-micro-founded models can provide explanations for those phenomena, even if those explanations are not fully satisfactory, what basis is there for rejecting them just because of a methodological precept that disqualifies all non-micro-founded models?

According to Kevin Hoover, the basis for insisting that only micro-founded macroeconomic models are acceptable, even if the microfoundation consists in a single representative agent optimizing for an entire economy, is eschatological. In other words, because of a belief that economics will eventually develop analytical or computational techniques sufficiently advanced to model an entire economy in terms of individual interacting agents, an analysis based on a single representative agent, as the first step on this theoretical odyssey, is somehow methodologically privileged over alternative models that do not share that destiny. Hoover properly rejects the presumptuous notion that an avowed, but unrealized, theoretical destiny, can provide a privileged methodological status to an explanatory strategy. The reductionist microfoundationalism of New-Classical macroeconomics and real-business-cycle theory, with which New Keynesian economists have formed an alliance of convenience, is truly a faith-based macroeconomics.

The remarkable similarity between the reductionist microfoundational methodology of New-Classical macroeconomics and the reductionist materialist approach to the concept of mind suggests to me that there is also a close analogy between the representative agent and what philosophers of mind call a homunculus. The Cartesian materialist theory of mind maintains that, at some place or places inside the brain, there resides information corresponding to our conscious experience. The question then arises: how does our conscious experience access the latent information inside the brain? And the answer is that there is a homunculus (or little man) that processes the information for us so that we can perceive it through him. For example, the homunculus (see the attached picture of the little guy) views the image cast by light on the retina as if he were watching a movie projected onto a screen.

homunculus

But there is an obvious fallacy, because the follow-up question is: how does our little friend see anything? Well, the answer must be that there’s another, smaller, homunculus inside his brain. You can probably already tell that this argument is going to take us on an infinite regress. So what purports to be an explanation turns out to be just a form of question-begging. Sound familiar? The only difference between the representative agent and the homunculus is that the representative agent begs the question immediately without having to go on an infinite regress.

PS I have been sidetracked by other responsibilities, so I have not been blogging much, if at all, for the last few weeks. I hope to post more frequently, but I am afraid that my posting and replies to comments are likely to remain infrequent for the next couple of months.

All New Classical Models Are Subject to the Lucas Critique

Almost 40 years ago, Robert Lucas made a huge, but not quite original, contribution, when he provided a very compelling example of how the predictions of the then standard macroeconometric models used for policy analysis were inherently vulnerable to shifts in the empirically estimated parameters contained in the models, shifts induced by the very policy change under consideration. Insofar as those models could provide reliable forecasts of the future course of the economy, it was because the policy environment under which the parameters of the model had been estimated was not changing during the time period for which the forecasts were made. But any forecast deduced from the model conditioned on a policy change would necessarily be inaccurate, because the policy change itself would cause the agents in the model to alter their expectations in light of the policy change, causing the parameters of the model to diverge from their previously estimated values. Lucas concluded that only models based on deep parameters reflecting the underlying tastes, technology, and resource constraints under which agents make decisions could provide a reliable basis for policy analysis.

The Lucas critique undoubtedly conveyed an important insight about how to use econometric models in analyzing the effects of policy changes, and if it did no more than cause economists to be more cautious in offering policy advice based on their econometric models and policy makers to more skeptical about the advice they got from economists using such models, the Lucas critique would have performed a very valuable public service. Unfortunately, the lesson that the economics profession learned from the Lucas critique went far beyond that useful warning about the reliability of conditional forecasts potentially sensitive to unstable parameter estimates. In an earlier post, I discussed another way in which the Lucas Critique has been misapplied. (One responsible way to deal with unstable parameter estimates would be make forecasts showing a range of plausible outcome depending on how parameter estimates might change as a result of the policy change. Such an approach is inherently messy, and, at least in the short run, would tend to make policy makers less likely to pay attention to the policy advice of economists. But the inherent sensitivity of forecasts to unstable model parameters ought to make one skeptical about the predictions derived from any econometric model.)

Instead, the Lucas critique was used by Lucas and his followers as a tool by which to advance a reductionist agenda of transforming macroeconomics into a narrow slice of microeconomics, the slice being applied general-equilibrium theory in which the models required drastic simplification before they could generate quantitative predictions. The key to deriving quantitative results from these models is to find an optimal intertemporal allocation of resources given the specified tastes, technology and resource constraints, which is typically done by describing the model in terms of an optimizing representative agent with a utility function, a production function, and a resource endowment. A kind of hand-waving is performed via the rational-expectations assumption, thereby allowing the optimal intertemporal allocation of the representative agent to be identified as a composite of the mutually compatible optimal plans of a set of decentralized agents, the hand-waving being motivated by the Arrow-Debreu welfare theorems proving that any Pareto-optimal allocation can be sustained by a corresponding equilibrium price vector. Under rational expectations, agents correctly anticipate future equilibrium prices, so that market-clearing prices in the current period are consistent with full intertemporal equilibrium.

What is amazing – mind-boggling might be a more apt adjective – is that this modeling strategy is held by Lucas and his followers to be invulnerable to the Lucas critique, being based supposedly on deep parameters reflecting nothing other than tastes, technology and resource endowments. The first point to make – there are many others, but we needn’t exhaust the list – is that it is borderline pathological to convert a valid and important warning about how economic models may be subject to misunderstanding or misuse as a weapon with which to demolish any model susceptible of such misunderstanding or misuse as a prelude to replacing those models by the class of reductionist micromodels that now pass for macroeconomics.

But there is a second point to make, which is that the reductionist models adopted by Lucas and his followers are no less vulnerable to the Lucas critique than the models they replaced. All the New Classical models are explicitly conditioned on the assumption of optimality. It is only by positing an optimal solution for the representative agent that the equilibrium price vector can be inferred. The deep parameters of the model are conditioned on the assumption of optimality and the existence of an equilibrium price vector supporting that equilibrium. If the equilibrium does not obtain – the optimal plans of the individual agents or the fantastical representative agent becoming incapable of execution — empirical estimates of the parameters of the model parameters cannot correspond to the equilibrium values implied by the model itself. Parameter estimates are therefore sensitive to how closely the economic environment in which the parameters were estimated corresponded to conditions of equilibrium. If the conditions under which the parameters were estimated more nearly approximated the conditions of equilibrium than the period in which the model is being used to make conditional forecasts, those forecasts, from the point of view of the underlying equilibrium model, must be inaccurate. The Lucas critique devours its own offspring.


About Me

David Glasner
Washington, DC

I am an economist in the Washington DC area. My research and writing has been mostly on monetary economics and policy and the history of economics. In my book Free Banking and Monetary Reform, I argued for a non-Monetarist non-Keynesian approach to monetary policy, based on a theory of a competitive supply of money. Over the years, I have become increasingly impressed by the similarities between my approach and that of R. G. Hawtrey and hope to bring Hawtrey's unduly neglected contributions to the attention of a wider audience.

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