Chris Sims explains why he got a Nobel Prize:
Tapp: So, if I asked you to describe the main contribution of your work to the field of economic modeling and maybe relating back to the traditional model, how would you describe that?
Sims: I think that what the Noble Prize people were singling out was that my work helped sort out the dispute between the monetarists and Keynesians. They, in part by introducing new approaches to statistical modeling in the '60s and early '70s, monetarists were claiming that the main source of business cycle fluctuations was bad monetary policy. The monetary authority was making mistakes, making the growth rate of money vary a lot, and all those variations resulted in recessions and booms, and if only we could force the monetary authority to stop messing with the economy and just keep money growth steady, the business cycle would be greatly reduced or even vanish.
And then the Keynesians were saying that can't be true, but they didn't have statistical models in which they could each put forward their position and ask, well, what did the data say? There were lots of attempts to do that, but with very awkward statistical modeling.
Over the course of about 10 years, things that I did and other people followed up on managed to sort out what the effects of monetary policy changes are and distinguish those from co-movements in money and prices and income that didn't have anything to do with policy. There's now pretty much a consensus on how monetary policy affects the economy, and on what the size of that effect is. The general conclusion is that it accounts for maybe somewhere between zero and 20 or 25 percent of the fluctuations we see, but if you try to trace out historically, you can't blame any recession on monetary policy.
Now we need Chris Sims, or someone like him, to lead the charge against the idea that the problem with the economy is bad fiscal policy. Even better would be if they could overcome the objections to the use of fiscal policy in severe recessions -- i.e. the type of recession that monetary policy alone cannot cure even if the interest rate is lowered to zero and non-traditional policies are put into place. In this case though, the empirical evidence is already mounting, what is needed are strong, respected voices to counter the objections to fiscal policy coming from the right (particularly, though not exclusively, objections to infrastructure investment). The politics of fiscal policy will always be a problem, but it would be less so if economists had the same unity on fiscal policy, particularly its ability to help the economy is severe recessions, that they have on monetary policy.