Christoph has recently vented his frustration about “DSGE bashing” now popular in the econ blogosphere. I feel this frustration, too, not because I believe DSGEs are perfect, but because I think that much of the popular criticism is ill-informed. Since I have worked with DSGE models recently in my research, I can call myself a card-carrying member of the club of DSGE aficionados. So I thought I briefly explain why I like DSGEs and what I think they are good for.
I think of DSGE models as applying ordinary principles of economics – optimizing behavior and market equilibrium (GE for general equilibrium) – to a world that evolves over time (D for dynamic) and is subject to chance (S for stochastic). When I say optimizing behavior I don’t necessarily mean rational expectations and when I say equilibrium I don’t necessarily mean market clearing. There are DSGEs without rational expectations and with non-clearing markets out there, although admittedly they are not the most widely used ones. I find this general approach attractive, because it brings us closer to a Unified Economic Science that uses a single set of principles to explain phenomena at the micro level and at the macro level.
But that’s not the most important reason I like DSGEs, which is that it makes precise and thus helps clarify commonly held notions about business cycles, economic crises and economic. Take, for instance, the notion of “recession”. In popular discussion a “recession” is when GDP growth is negative or at least below what is conceived a normal or desirable rate. In DSGE models, a recession is a negative output gap: the difference between the actual level of output and that level which would occur if prices were fully flexible (the “natural rate of output”). DSGEs make it clear that a negative growth rate is not necessarily bad (if the weather is bad in April and better in May, you want production to go down in April and up in May) and a positive growth rate not necessarily good (two percent real growth can sometimes mean an overheating economy and sometimes be a sluggish one). You have to look at more than one variable (at least two, output growth and inflation) to decide whether the economy is in good or bad shape.
Another reason I like DSGEs is that they discuss economic policy in a much more coherent and sensible manner than most of the earlier literature – and much more so than the financial press. The important question about any policy X is not “Does X increase GDP or reduce unemployment or increase asset prices?”, but “Does X increase the utility of households?”. Also, because DSGEs are dynamic models, they put the focus on policy rules, i.e. how policymakers behave across time and in different situations, instead of looking only what policymakers do right now and in this particular situation.
There is a lot of valid criticism against DSGEs: they often are too simplistic and sweep important but hard-to-model aspects under the rug and they, as a result of that, have lots of empirical issues. But these things should encourage us to make DSGEs better, not return to the even more simplistic approaches that previously dominated macroeconomics.