Posts Tagged 'Lucas Critique'

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.


The Near Irrelevance of the Vertical Long-Run Phillips Curve

From a discussion about how much credit Milton Friedman deserves for changing the way that economists thought about inflation, I want to nudge the conversation in a slightly different direction, to restate a point that I made some time ago in one of my favorite posts (The Lucas Critique Revisited). But if Friedman taught us anything it is that incessant repetition of the same already obvious point can do wonders for your reputation. That’s one lesson from Milton that I am willing to take to heart, though my tolerance for hearing myself say the same darn thing over and over again is probably not as great as Friedman’s was, which to be sure is not the only way in which I fall short of him by comparison. (I am almost a foot taller than he was by the way). Speaking of being a foot taller than Friedman, I don’t usually post pictures on this blog, but here is one that I have always found rather touching. And if you don’t know who the other guy is in the picture, you have no right to call yourself an economist.

friedman_&_StiglerAt any rate, the expectations augmented, long-run Phillips Curve, as we all know, was shown by Friedman to be vertical. But what exactly does it mean for the expectations-augmented, long-run Phillips Curve to be vertical? Discussions about whether the evidence supports the proposition that the expectations-augmented, long-run Phillips Curve is vertical (including some of the comments on my recent posts) suggest that people are not clear on what “long-run” means in the context of the expectations-augmented Phillips Curve and have not really thought carefully about what empirical content is contained by the proposition that the expectations-augmented, long-run Phillips Curve is vertical.

Just to frame the discussion of the Phillips Curve, let’s talk about what the term “long-run” means in economics. What it certainly does not mean is an amount of calendar time, though I won’t deny that there are frequent attempts to correlate long-run with varying durations of calendar time. But all such attempts either completely misunderstand what the long-run actually represents, or they merely aim to provide the untutored with some illusion of concreteness in what is otherwise a completely abstract discussion. In fact, what “long run” connotes is simply a full transition from one equilibrium state to another in the context of a comparative-statics exercise.

If a change in some exogenous parameter is imposed on a pre-existing equilibrium, then the long-run represents the full transition to a new equilibrium in which all endogenous variables have fully adjusted to the parameter change. The short-run, then, refers to some intermediate adjustment to the parameter change in which some endogenous variables have been arbitrarily held fixed (presumably because of some possibly reasonable assumption that some variables are able to adjust more speedily than other variables to the posited parameter change).

Now the Phillips Curve that was discovered by A. W. Phillips in his original paper was a strictly empirical relation between observed (wage) inflation and observed unemployment. But the expectations-augmented long-run Phillips Curve is a theoretical construct. And what it represents is certainly not an observable relationship between inflation and unemployment; it rather is a locus of points of equilibrium, each point representing full adjustment of the labor market to a particular rate of inflation, where full adjustment means that the rate of inflation is fully anticipated by all economic agents in the model. So what the expectations-augmented, long-run Phillips Curve is telling us is that if we perform a series of comparative-statics exercises in which, starting from full equilibrium with the given rate of inflation fully expected, we impose on the system a parameter change in which the exogenously imposed rate of inflation is changed and deduce a new equilibrium in which the fully and universally expected rate of inflation equals the alternative exogenously imposed inflation parameter, the equilibrium rate of unemployment corresponding to the new inflation parameter will not differ from the equilibrium rate of unemployment corresponding to the original inflation parameter.

Notice, as well, that the expectations-augmented, long-run Phillips Curve is not saying that imposing a new rate of inflation on an actual economic system would lead to a new equilibrium in which there was no change in unemployment; it is merely comparing alternative equilibria of the same system with different exogenously imposed rates of inflation. To make a statement about the effect of a change in the rate of inflation on unemployment, one has to be able to specify an adjustment path in moving from one equilibrium to another. The comparative-statics method says nothing about the adjustment path; it simply compares two alternative equilibrium states and specifies the change in endogenous variable induced by the change in an exogenous parameter.

So the vertical shape of the expectations-augmented, long-run Phillips Curve tells us very little about how, in any given situation, a change in the rate of inflation would actually affect the rate of unemployment. Not only does the expectations-augmented long-run Phillips Curve fail to tell us how a real system starting from equilibrium would be affected by a change in the rate of inflation, the underlying comparative-statics exercise being unable to specify the adjustment path taken by a system once it departs from its original equilibrium state, the expectations augmented, long-run Phillips Curve is even less equipped to tell us about the adjustment to a change in the rate of inflation when a system is not even in equilibrium to begin with.

The entire discourse of the expectations-augmented, long-run Phillips Curve is completely divorced from the kinds of questions that policy makers in the real world usually have to struggle with – questions like will increasing the rate of inflation of an economy in which there is abnormally high unemployment facilitate or obstruct the adjustment process that takes the economy back to a more normal unemployment rate. The expectations-augmented, long-run Phillips Curve may not be completely irrelevant to the making of economic policy – it is good to know, for example, that if we are trying to figure out which time path of NGDP to aim for, there is no particular reason to think that a time path with a 10% rate of growth of NGDP would probably not generate a significantly lower rate of unemployment than a time path with a 5% rate of growth – but its relationship to reality is sufficiently tenuous that it is irrelevant to any discussion of policy alternatives for economies unless those economies are already close to being in equilibrium.

Scott Sumner, Meet Robert Lucas

I just saw Scott Sumner’s latest post. It’s about the zero fiscal multiplier. Scott makes a good and important point, which is that, under almost any conditions, fiscal policy cannot be effective if monetary policy is aiming at a policy objective that is inconsistent with that fiscal policy. Here’s how Scott puts it in his typical understated fashion.

From today’s news:

The marked improvement in the labor market since the U.S. central bank began its third round of quantitative easing, or QE3, has added an edge to calls by some policy hawks to dial down the stimulus. The roughly 50 percent jump in monthly job creation since the program began has even won renewed support from centrists, raising at least some chance the Fed could ratchet back its buying as early as next month.

I hope I don’t have to do any more of these.  The fiscal multiplier theory is as dead as John Cleese’s parrot.  The growth in jobs didn’t slow with fiscal austerity, it sped up!  And the Fed is saying that any job improvement due to fiscal stimulus will be offset with tighter money.  They talk like the multiplier is zero, and their actions produce a zero multiplier.

This is classic Sumner, and he deserves credit for rediscovering an argument that Ralph Hawtrey made in 1925, but was ignored and then forgotten until Sumner figured it out for himself. When I went through Hawtrey’s analysis in my recent series of posts on Hawtrey and Keynes, Scott immediately identified the identity between what Hawtrey was saying and what he was saying. So up to this point, I am with Scott all the way. But then he loses me, by asking the following question

Has there ever been a more decisive refutation of a major economic theory?

What’s wrong with that question? Well, it seems to me to fly in the face of another critique by another famous economist whom, I think, Scott actually knows: Robert Lucas. Almost 40 years ago, Lucas published a paper about the Phillips Curve in which he argued that the existence of an empirical relationship between inflation and unemployment, even if empirically well-founded, was not a relationship that policy makers could use as a basis for their policy decisions, because the expectations (of low inflation or stable prices) under which the negative relationship between inflation and unemployment was observed would break down once policy makers used that relationship to try to reduce unemployment by increasing inflation. That simple point, dressed up with just enough mathematical notation to obscure its obviousness, helped Lucas win the Noble Prize, and before long became widely known as the Lucas Critique.

The crux of the Lucas Critique is that economic theory posits deep structural relationships governing economic activity. These structural relationships are necessarily sensitive to the expectations of decision makers, so that no observed empirical relationship between economic variables is invariant to the expectational effects of the policy rules governing policy decisions. Observed relationships between economic variables are useless for policy makers unless they understand those deep structural relationships and how they are affected by expectations.

But now Scott seems to be turning the Lucas Critique on its head by saying that the expectations that result from a particular policy regime — a policy regime that has been subjected to withering criticism by none other than Scott himself – refutes a structural theory (that government spending can increase aggregate spending and income) of how the economy works. I don’t think so. The fact that the Fed has adopted and tenaciously sticks to a perverse reaction function cannot refute a theory in which the Fed’s reaction function is a matter of choice not necessity.

I agree with Scott that monetary policy is usually the best tool for macroeconomic stabilization. But that doesn’t mean that fiscal policy can never ever promote recovery. Even Ralph Hawtrey, originator of the “Treasury view” that fiscal policy is powerless to affect aggregate spending, acknowledged that, in a credit deadlock, when expectations are so pessimistic that the monetary authority is powerless to increase private spending, deficit spending by the government financed by money creation might be the only way to increase aggregate spending. That, to be sure, is a pathological situation. But, with at least some real interest rates, currently below zero, it is not impossible to suppose that we are, or have been, in something like a Hawtreyan credit deadlock. I don’t say that we are in one, just that it’s possible that we are close enough to being there that we can’t confidently exclude the possibility, if only the Fed would listen to Scott and stop targeting 2% inflation, of a positive fiscal multiplier.

With US NGDP not even increasing at a 4% annual rate, and the US economy far below its pre-2008 trendline of 5% annual NGDP growth, I don’t understand why one wouldn’t welcome the aid of fiscal policy in getting NDGP to increase at a faster rate than it has for the last 5 years. Sure the economy has been expanding despite a sharp turn toward contractionary fiscal policy two years ago. If fiscal stimulus had not been withdrawn so rapidly, can we be sure that the economy would not have grown faster? Under conditions such as these, as Hawtrey himself well understood, the prudent course of action is to err on the side of recklessness.

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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