Are Macroeconomic Models Useful?
There has been no shortage of effort devoted to predicting earthquakes, yet we still can't see them coming far enough in advance to move people to safety. When a big earthquake hits, it is a surprise. We may be able to look at the data after the fact and see that certain stresses were building, so it looks like we should have known an earthquake was going to occur at any moment, but these sorts of retrospective analyses have not allowed us to predict the next one. The exact timing and location is always a surprise.
Does that mean that science has failed? Should we criticize the models as useless?
No. There are two uses of models. One is to understand how the world works, another is to make predictions about the future. We may never be able to predict earthquakes far enough in advance and with enough specificity to allow us time to move to safety before they occur, but that doesn't prevent us from understanding the science underlying earthquakes. Perhaps as our understanding increases prediction will be possible, and for that reason scientists shouldn't give up trying to improve their models, but for now we simply cannot predict the arrival of earthquakes.
However, even though earthquakes cannot be predicted, at least not yet, it would be wrong to conclude that science has nothing to offer. First, understanding how earthquakes occur can help us design buildings and make other changes to limit the damage even if we don't know exactly when an earthquake will occur. Second, if an earthquake happens and, despite our best efforts to insulate against it there are still substantial consequences, science can help us to offset and limit the damage. To name just one example, the science surrounding disease transmission helps use to avoid contaminated water supplies after a disaster, something that often compounds tragedy when this science is not available. But there are lots of other things we can do as well, including using the models to determine where help is most needed.
So even if we cannot predict earthquakes, and we can't, the models are still useful for understanding how earthquakes happen. This understanding is valuable because it helps us to prepare for disasters in advance, and to determine policies that will minimize their impact after they happen.
All of this can be applied to macroeconomics. Whether or not we should have predicted the financial earthquake is a question that has been debated extensively, so I am going to set that aside. One side says financial market price changes, like earthquakes, are inherently unpredictable -- we will never predict them no matter how good our models get (the efficient markets types). The other side says the stresses that were building were obvious. Like the stresses that build when tectonic plates moving in opposite directions rub against each other, it was only a question of when, not if. (But even when increasing stress between two plates is observable, scientists cannot tell you for sure if a series of small earthquakes will relieve the stress and do little harm, or if there will be one big adjustment that relieves the stress all at once. With respect to the financial crisis, economists expected lots of little, small harm causing adjustments, instead we got the "big one," and the "buildings and other structures" we thought could withstand the shock all came crumbling down. On prediction in economics, perhaps someday improved models will allow us to do better than we have so far at predicting the exact timing of crises, and I think that earthquakes provide some guidance here. You have to ask first if stress is building in a particular sector, and then ask if action needs to be taken because the stress has reached dangerous levels, levels that might result in a big crash rather than a series of small stress relieving adjustments. I don't think our models are very good at detecting accumulating stress, in large part because when we are not at the long-run equilibrium, we model the short-run as though every market clears at every point in time. This means that there are no stresses continuously building in these models, the adjustments always relieve the stress and move us back toward long-run equilibrium. We have to do a better job of allowing for the build up of stress within our models, and then using these models to guide the measurement and monitoring of "stress levels" in particular markets, particularly asset markets, so we can take action when the levels are too high.)
Whether the financial crisis should have been predicted or not, the fact that it wasn't predicted does not mean that macroeconomic models are useless any more than the failure to predict earthquakes implies that earthquake science is useless. As with earthquakes, even when prediction is not possible (or missed), the models can still help us to understand how these shocks occur. That understanding is useful for getting ready for the next shock, or even preventing it, and for minimizing the consequences of shocks that do occur.
But we have done much better at dealing with the consequences of unexpected shocks ex-post than we have at getting ready for these a priori. Our equivalent of getting buildings ready for an earthquake before it happens is to use changes in institutions and regulations to insulate the financial sector and the larger economy from the negative consequences of financial and other shocks. Here I think economists made mistakes - our "buildings" were not strong enough to withstand the earthquake that hit. We could argue that the shock was so big that no amount of reasonable advance preparation would have stopped the "building" from collapsing, but I think it's more the case that enough time has passed since the last big financial earthquake that we forgot what we needed to do. We allowed new buildings to be constructed without the proper safeguards.
However, that doesn't mean the models themselves were useless. The models were there and could have provided guidance, but the implied "building codes" were ignored. Greenspan and others assumed no private builder would ever construct a building that couldn't withstand an earthquake, the market would force them to take this into consideration. But they were wrong about that, and even Greenspan now admits that government building codes are necessary. It wasn't the models, it was how they were used (or rather not used) that prevented us from putting safeguards into place.
We haven't failed at this entirely though. For example, we have had some success at putting safeguards into place before shocks occur, automatic stabilizers have done a lot to insulate against the negative consequences of the recession (though they could have been larger to stop the building from swaying as much as it has). So it's not proper to say that our models have not helped us to prepare in advance at all, the insulation social insurance programs provide is extremely important to recognize. But it is the case that we could have and should have done better at preparing before the shock hit.
I'd argue that our most successful use of models has been in cleaning up after shocks rather than predicting, preventing, or insulating against them through pre-crisis preparation. When despite our best effort to prevent it or to minimize its impact a priori, we get a recession anyway, we can use our models as a guide to monetary, fiscal, and other policies that help to reduce the consequences of the shock (this is the equivalent of, after a disaster hits, making sure that the water is safe to drink, people have food to eat, there is a plan for rebuilding quickly and efficiently, etc.). As noted above, we haven't done a very good job at predicting big crises, and we could have done a much better job at implementing regulatory and institutional changes that prevent or limit the impact of shocks. But we do a pretty good job of stepping in with policy actions that minimize the impact of shocks after they occur. This recession was bad, but it wasn't another Great Depression like it might have been without policy intervention.
Whether or not we will ever be able to predict recessions reliably, it's important to recognize that our models still provide considerable guidance for actions we can take before and after large shocks that minimize their impact and maybe even prevent them altogether (though we will have to do a better job of listening to what the models have to say). Prediction is important, but it's not the only use of models.
Posted by Mark Thoma on Tuesday, August 25, 2009 at 03:33 PM in Economics, Macroeconomics, Methodology |
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