Zelo razumna introspekcija Simona Wrena-Lewisa, ki sicer uporablja DSGE modele, o tem, kaj je v teh modelih koristnega, kaj je podcenjenega in zakaj so “ad hoc” ali hibridni modeli velikokrat boljši. Ključen problem je po njegovem v podcenjevanju brezposelnosti na račun inflacije (kar izhaja iz monetarističnega pristopa, ki ga v osnovi zanima inflacija, medtem ko na nezaposlenost glede kot na prostovoljno odločitev, kjer posameznik tehta med prostim časom in delom). Zato namesto običajno ideološkega (samo DSGE modeli so dobri) predlaga povsem pragmatičen pristop, torej da se DSGE ne uporabljajo za simuliranje ekonomskih politik, kadar in kjer so drugi (ad hoc, agregatni) modeli boljši.

Opozarjam pa, da spodnje branje ni nujno prijazno do neekonomistov.

Many of the difficult choices in conducting monetary (and sometimes fiscal) policy involve trade-offs between inflation and unemployment. We saw this in the UK particularly after the crisis, with inflation going well above target during the depth of the recession. What you do in those circumstances depends critically on the costs of excess inflation compared to the costs of higher unemployment. Is 1% higher unemployment worth more or less than 1% higher inflation to society as a whole?

What do New Keynesian DSGE models say about this trade-off? They do not normally model unemployment, but they do model the output gap, which we can relate to unemployment. Their answer is that inflation is much the more important variable, by a factor of ten or more. One reason they do this is that they implicitly assume the unemployed enjoy all the extra leisure time at their disposal. I have discussed other reasons here.

Empirical evidence, and frankly common sense, suggests this is the wrong answer. Thanks to the emergence of a literature that looks at empirical measures of wellbeing, we now have clear evidence that unemployment matters more than inflation. Sometimes, as in this study by Blanchflower et al, it matters much more. Another recent study by economists at the CEP shows that “life satisfaction of individuals is between two and eight times more sensitive to periods when the economy is shrinking than at times of growth”, which as well as being related to the unemployment/inflation trade-off raises additional issues around asymmetry.

So the DSGE models appear to be dead wrong. Furthermore the reasons why they are wrong are not deeply mysterious, and certainly not mysterious enough to make us question the evidence. For example prolonged spells of unemployment have well documented scarring effects (in part because employers cannot tell if unemployment was the result of bad luck or bad performance), which may even affect the children of the unemployed. So it is not as if economists cannot understand the empirical evidence.

Does that mean that the DSGE models are deeply flawed? No, it means they are much too simple. Does that mean that the work behind them (deriving social welfare functions from individual utility) is a waste of time? I would again say no. I have done a little work of this kind, and I understood some things much better by doing so. Will these models ever get close to the data? I do not know, but I think we will learn more interesting and useful things in the attempt. The microfoundations methodology is, in my view, a progressive research strategy.

So academics are right to carry on working with these models. But many academic macroeconomists go further than this. They argue that only microfounded DSGE models can provide a sound basis for policy advice. If you press them they will say that maybe it is OK for policymakers to use more ‘ad hoc’ models, but there is no place for these in the academic journals. In my view this is absolutely wrong for at least two reasons.

First, models that are clearly still at the early development stage should not be used to guide policy when we can clearly do better. In this particular case we can easily do better just by using ad hoc social welfare functions on top of an existing DSGE model. (The Lucas critique does not apply, which is why I like this example.) Yes these hybrid models will be ‘internally inconsistent’, but they are clearly better!

Second, to confine academics to just doing development work on prototype experimental models is stupid: academic economists can have many useful things to say starting with aggregate models (as here, for example), and this is not something that policymakers alone have the resources (or sometimes the inclination) to do. (We also know that academics will give policy advice, whatever models they use!) Analysis using these more ad hoc but realistic models should be scrutinised in high quality academic journals.

Vir: Simon Wren-Lewis