Blanchard: On the Need for (At Least) Five Classes of Macro Models

Olivier Blanchard:

On the Need for (At Least) Five Classes of Macro Models: One of the best pieces of advice Rudi Dornbusch gave me was: Never talk about methodology. Just do it. Yet, I shall disobey and take the plunge.

The reason and the background for this blog is a project started by David Vines about DSGEs, how they performed in the crisis, and how they could be improved.[1] Needled by his opinions, I wrote a PIIE Policy Brief. Then, in answer to the comments to the brief, I wrote a PIIE RealTime blog. And yet a third, another blog, each time hopefully a little wiser. I thought I was done, but David organized a one-day conference on the topic, from which I learned a lot and which has led me to write my final (?) piece on the topic.

This piece has a simple theme: We need different types of macro models. One type is not better than the other. They are all needed, and indeed they should all interact. Such remarks would be trivial and superfluous if that proposition were widely accepted, and there were no wars of religion. But it is not, and there are.

Here is my attempt at typology, distinguishing between five types. (I limit myself to general equilibrium models. Much of macro must, however, be about building the individual pieces, constructing partial equilibrium models, and examining the corresponding empirical micro and macro evidence, pieces on which the general equilibrium models must then build.) In doing so, I shall, with apologies, repeat some of what was in the previous blogs. ...