John Cochrane writes,
Greg Mankiw has a nice op-ed on dynamic scoring
The issue: When the congressional budget office “scores” legislation, figuring out how much it will raise or lower tax revenue and spending, it has been using “static” scoring. For example, it assumes that a tax cut has no effect on GDP, even if the whole point of the tax cut is to raise GDP.
My thoughts.
1. I am against dynamic scoring. Dynamic scoring means using an economic model. I think that politicians and the press give too much credence to economic models as it is. Even static scoring requires some modeling, but the modeling has more to do with spreadsheet arithmetic as opposed to claiming to be able to predict economic behavior.
2. To the extent that the CBO has to predict economic behavior, I think it should present several scenarios, as opposed to a point estimate or a range. Cochrane says it well:
It’s a fact, we don’t know the elasticities, multipliers, and mechanisms that well. So stop pretending. Stop producing only a single number, accurate to three decimals. Instead, present a range of scenarios spanning the range of reasonable uncertainty about responses.
Responding to another point from Cochrane, Mankiw writes,
you need to specify how the government is going to satisfy its present-value budget constraint. You might be tempted to ask the model what happens if the government cuts taxes and never does anything else. But you won’t get very far. The model will tell you that the government has to do something else eventually, and it won’t tell you what will happen if the government tries to do something impossible.
What I hear Greg saying is that to properly do dynamic scoring, you would need to include a model of future policy responses. That is a point well taken, but I am not sure that I would restrict those policy responses to be only doing things that are possible. Policy makers are doing impossible (that is, unsustainable) things now. The challenge is to predict the outcome of undertaking unsustainable policies until you cannot do so any more.
Of course, the traditional “static” scoring does not solve the problem of how to predict the outcome of unsustainable policies, either.