Reform and revolution in macroeconomics

Mainly for economists

Paul Romer has a few recent posts (start here, most recent here) where he tries to examine why the saltwater/freshwater divide in macroeconomics happened. A theme is that this cannot all be put down to New Classical economists wanting a revolution, and that a defensive/dismissive attitude from the traditional Keynesian status quo also had a lot to do with it.

I will leave others to discuss what Solow said or intended (see for example Robert Waldmann). However I have no doubt that many among the then Keynesian status quo did react in a defensive and dismissive way. They were, after all, on incredibly weak ground. That ground was not large econometric macromodels, but one single equation: the traditional Phillips curve. This had inflation at time t depending on expectations of inflation at time t, and the deviation of unemployment/output from its natural rate. Add rational expectations to that and you show that deviations from the natural rate are random, and Keynesian economics becomes irrelevant. As a result, too many Keynesian macroeconomists saw rational expectations (and therefore all things New Classical) as an existential threat, and reacted to that threat by attempting to rubbish rational expectations, rather than questioning the traditional Phillips curve. As a result, the status quo lost. [1]

We now know this defeat was temporary, because New Keynesians came along with their version of the Phillips curve and we got a new ‘synthesis’. But that took time, and you can describe what happened in the time in between in two ways. You could say that the New Classicals always had the goal of overthrowing (rather than improving) Keynesian economics, thought that they had succeeded, and simply ignored New Keynesian economics as a result. Or you could say that the initially unyielding reaction of traditional Keynesians created an adversarial way of doing things whose persistence Paul both deplores and is trying to explain. (I have no particular expertise on which story is nearer the truth. I went with the first in this post, but I’m happy to be persuaded by Paul and others that I was wrong.) In either case the idea is that if there had been more reform rather than revolution, things might have gone better for macroeconomics.

The point I want to discuss here is not about Keynesian economics, but about even more fundamental things: how evidence is treated in macroeconomics. You can think of the New Classical counter revolution as having two strands. The first involves Keynesian economics, and is the one everyone likes to talk about. But the second was perhaps even more important, at least to how academic macroeconomics is done. This was the microfoundations revolution, that brought us first RBC models and then DSGE models. As Paul writes:

“Lucas and Sargent were right in 1978 when they said that there was something wrong, fatally wrong, with large macro simulation models. Academic work on these models collapsed.”

The question I want to raise is whether for this strand as well, reform rather than revolution might have been better for macroeconomics.

First two points on the quote above from Paul. Of course not many academics worked directly on large macro simulation models at the time, but what a large number did do was either time series econometric work on individual equations that could be fed into these models, or analyse small aggregate models whose equations were not microfounded, but instead justified by an eclectic mix of theory and empirics. That work within academia did largely come to a halt, and was replaced by microfounded modelling.

Second, Lucas and Sargent’s critique was fatal in the sense of what academics subsequently did (and how they regarded these econometric simulation models), although they got a lot of help from Sims (1980). But it was not fatal in a more general sense. As Brad DeLong points out, these econometric simulation models survived both in the private and public sectors (in the US Fed, for example, or the UK OBR). In the UK they survived within the academic sector until the latter 1990s when academics helped kill them off.

I am not suggesting for one minute that these models are an adequate substitute for DSGE modelling. There is no doubt in my mind that DSGE modelling is a good way of doing macro theory, and I have learnt a lot from doing it myself. It is also obvious that there was a lot wrong with large econometric models in the 1970s. My question is whether it was right for academics to reject them completely, and much more importantly avoid the econometric work that academics once did that fed into them.

It is hard to get academic macroeconomists trained since the 1980s to address this question, because they have been taught that these models and techniques are fatally flawed because of the Lucas critique and identification problems. But DSGE models as a guide for policy are also fatally flawed because they are too simple. The unique property that DSGE models have is internal consistency. Take a DSGE model, and alter a few equations so that they fit the data much better, and you have what could be called a structural econometric model. It is internally inconsistent, but because it fits the data better it may be a better guide for policy.

What happened in the UK in the 1980s and 1990s is that structural econometric models evolved to minimise Lucas critique problems by incorporating rational expectations (and other New Classical ideas as well), and time series econometrics improved to deal with identification issues. If you like, you can say that structural econometric models became more like DSGE models, but where internal consistency was sacrificed when it proved clearly incompatible with the data.

These points are very difficult to get across to those brought up to believe that structural econometric models of the old fashioned kind are obsolete, and fatally flawed in a more fundamental sense. You will often be told that to forecast you can either use a DSGE model or some kind of (virtually) atheoretical VAR, or that policymakers have no alternative when doing policy analysis than to use a DSGE model. Both statements are simply wrong.

There is a deep irony here. At a time when academics doing other kinds of economics have done less theory and become more empirical, macroeconomics has gone in the opposite direction, adopting wholesale a methodology that prioritised the internal theoretical consistency of models above their ability to track the data. An alternative - where DSGE modelling informed and was informed by more traditional ways of doing macroeconomics - was possible, but the New Classical and microfoundations revolution cast that possibility aside.

Did this matter? Were there costs to this strand of the New Classical revolution?

Here is one answer. While it is nonsense to suggest that DSGE models cannot incorporate the financial sector or a financial crisis, academics tend to avoid addressing why some of the multitude of work now going on did not occur before the financial crisis. It is sometimes suggested that before the crisis there was no cause to do so. This is not true. Take consumption for example. Looking at the (non-filtered) time series for UK and US consumption, it is difficult to avoid attaching significant importance to the gradual evolution of credit conditions over the last two or three decades (see the references to work by Carroll and Muellbauer I give in this post). If this kind of work had received greater attention (which structural econometric modellers would almost certainly have done), that would have focused minds on why credit conditions changed, which in turn would have addressed issues involving the interaction between the real and financial sectors. If that had been done, macroeconomics might have been better prepared to examine the impact of the financial crisis.

It is not just Keynesian economics where reform rather than revolution might have been more productive as a consequence of Lucas and Sargent, 1979.

[1] The point is not whether expectations are generally rational or not. It is that any business cycle theory that depends on irrational inflation expectations appears improbable. Do we really believe business cycles would disappear if only inflation expectations were rational? PhDs of the 1970s and 1980s understood that, which is why most of them rejected the traditional Keynesian position. Also, as Paul Krugman points out, many Keynesian economists were happy to incorporate New Classical ideas. 

The F story about the Great Inflation

Here F could stand for folk. The story that is often told by economists to their students goes as follows. After Phillips discovered his curve, which relates inflation to unemployment, Samuelson and Solow in 1960 suggested this implied a trade-off that policymakers could use. They could permanently have a bit less unemployment at the cost of a bit more inflation. Policymakers took up that option, but then could not understand why inflation didn’t just go up a bit, but kept on going up and up. Along came Milton Friedman to the rescue, who in a 1968 presidential address argued that inflation also depended on inflation expectations, which meant the long run Phillips curve was vertical and there was no permanent inflation unemployment trade-off. Policymakers then saw the light, and the steady rise in inflation seen in the 1960s and 1970s came to an end.

This is a neat little story, particularly if you like the idea that all great macroeconomic disasters stem from errors in mainstream macroeconomics. However even a half awake student should spot one small difficulty with this tale. Why did it take over 10 years for Friedman’s wisdom to be adopted by policymakers, while Samuelson and Solow’s alleged mistake seems to have been adopted quickly? Even if you think that the inflation problem only really started in the 1970s that imparts a 10 year lag into the knowledge transmission mechanism, which is a little strange.

However none of that matters, because this folk story is simply untrue. There has been some discussion of this in blogs (by Robert Waldmann in particular - see Mark Thoma here), and the best source on this is another F: James Forder. There are papers (e.g. here), but the most comprehensive source is now his book, which presents an exhaustive study of this folk story. It is, he argues, untrue in every respect. Not only did Samuelson and Solow not argue that there was a permanent inflation unemployment trade-off that policymakers could exploit, policymakers never believed there was such a trade-off. So how did this folk story arise? Quite simply from another F: Friedman himself, in his Nobel Prize lecture in 1977.

Forder discusses much else in his book, including the extent to which Friedman’s 1968 emphasis on the importance of expectations was particularly original (it wasn’t). He also describes how and why he thinks Friedman’s story became so embedded that it became folklore. The reason I write about this now is that I’m in the process of finishing a paper on the knowledge transmission mechanism and the 2010 switch to austerity, and I wanted to look back at previous macroeconomic crises.

If it wasn’t a belief in a long run inflation unemployment trade-off, what was it that allowed inflation to gradually rise during those two decades? Forder has a lot to say on this, but the following is my own take. I think two things were critical: the idea that demand management was primarily designed to achieve full employment, and that full employment had primacy over the objective of price stability. Although more and more economists over that period began to see the policy problem within a Phillips curve framework, many still hoped that other measures like prices and incomes policies (in the UK in particular but also in the US) could override the Phillips curve logic. The primacy of the full employment objective meant the problem was often described as ‘cost-push inflation’ rather than a rise in the natural rate of unemployment.

If you find this hard to imagine, think about historians discussing the current period in a possible future in 2050. By then nonlinearities in the Phillips curve and the power the inflation target had in anchoring inflation expectations were firmly entrenched in mainstream thinking. Imagine that partly as a result in 2050 the inflation target has been replaced by a level of nominal income target. With the benefit of hindsight these historians were amazed to calculate the extent to which resources were lost decades earlier because policy had become fixated by a 2% inflation target and budget deficits. They will recount with amusement at the number of economists and policymakers who thought that the way to deal with deficient demand was by ‘structural reform’. Rather than construct folk tales, they will observe that even when most economists realised what was required to avoid being misled again policymakers were extremely reluctant to change the inflation target.

Multipliers and evidence

I should be more careful with titles. The title of this post may have misled some (including Paul Krugman) to characterise what I was saying as favouring a priori beliefs over evidence. What I was in fact talking about was different kinds of evidence.

One kind of evidence on multipliers comes from directly relating output to some fiscal variable like government spending. In much the same way we could base monetary policy on attempts to relate output or inflation directly to changes in interest rates. This is sometimes called ‘reduced form’ estimation. As I said in my post, these studies are valuable, and if they repeatedly show something different from other evidence that would be worrying. However in my experience I have found them less reliable than evidence based on looking at the structure of the economy. I discuss a personal example here, but two more recent examples where reduced form evidence has not proved robust concern the impact of debt on growth and evidence supporting expansionary austerity.

As I wrote in the recent post: “My priors come from thinking about models, or perhaps more accurately mechanisms, that have a solid empirical foundation.” Again perhaps I was remiss in not emphasising that last clause, but it is critical. Robert Waldmann did interpret what I wrote correctly, but has a more worrying (for me) charge - that my view of what specific structural empirical evidence says is tempered by modern microfounded modelling.

A good example concerns how consumers might react to a temporary increase in income. I wrote that my prior is that consumers will largely discount temporary income changes. But what exactly do I mean by ‘largely’ here? Is a marginal propensity to consume out of temporary income of, say, 0.3 large or not? As I have noted elsewhere, there is good empirical evidence to support a number of that kind, and it is possible to explain this in terms of consumers optimising in the face of uncertainty. 

But the plain vanilla intertemporal consumption model implies a marginal propensity to consume out of temporary income close to (or identical to) zero. So when I wrote “largely discount”, did I in fact temper my knowledge of the empirical evidence because of this basic (and in macro ubiquitous) theory? Or was I attempting to use a form of words which was ambiguous enough not to upset those who did have a strong attachment to the plain vanilla model, which would have been just as bad.

It would be ironic if I had been. On a number of occasions I have argued that it was unfortunate that the microfoundations revolution has completely killed (in the academic literature, if not in all central banks) the alternative of analysing aggregate models where relationships are partly justified by empirical evidence. One of my reasons for believing this to be unfortunate is that it tends to put too much weight on simple theory relative to evidence. When I wrote ‘largely discount’ was I providing an example of just this kind of thing?

If it was, it may only have been a temporary lapse. Paul thinks a multiplier of around 1.5 is reasonable (I assume at the Zero Lower Bound when there will be little or no monetary policy offset), and when I wrote this I also assumed a multiplier of 1.5. However I think the point that Robert was making is a very important one: in macro we seem generally happier falling back on what standard theory says than on what the majority of empirical evidence suggests.