'A Slippery New Rule for Gauging Fiscal Policy'

Greg Mankiw:

A Slippery New Rule for Gauging Fiscal Policy: the case for dynamic over static scoring is strong in theory. Yet three problems make the task difficult in practice.

First, any attempt to estimate the impact of a policy change on G.D.P. requires an economic model. Because reasonable people can disagree about what model, and what parameters of that model, are best, the results from dynamic scoring will always be controversial. ...

Second, accurate dynamic scoring requires more information than congressional proposals typically provide. ...

Third, dynamic scoring matters most over long time horizons. Some policy changes, such as those aimed at encouraging capital investments, take many decades to have their full impact on economic growth. Yet congressional budgeting usually looks only five or 10 years ahead. ...

So there are good reasons for the economists hired by Congress to pursue dynamic scoring. But there are also good reasons to be wary of the endeavor. ...

Another worry is the politicization of the CBO. See here and here. Also see here and here on the application of dynamic scoring to things such as Head Start and infrastructure spending.

John Whitehead comments:

Mankiw on dynamic scoring: ...Mankiw:

First, any attempt to estimate the impact of a policy change on G.D.P. requires an economic model. Because reasonable people can disagree about what model, and what parameters of that model, are best, the results from dynamic scoring will always be controversial. Just as many Republicans are skeptical about the models of climatologists when debating global warming, many Democrats are skeptical about the models of economists when debating tax policy.

My read of the article was going just fine until the climate model analogy. Two assumptions are made:

1. All economists agree on "the models of economists" 
2. Reasonable people can disagree about climatology models

In terms of #1, there is significant disagreement amongst economists about macroeconomic models (i.e., have you read Krugman lately?). In terms of #2, science is different than social science. Climatology involves forecasts so it is different than tests of the law of gravity, but still, ninety-x percent of climate scientists agree. That is a bit higher than the number of economists who agree on anything macro. 

My stance is that we should accept that the earth is likely warming and people contribute to it (even the U.S. Senate, including those Republicans that Mankiw mentions [did he miss that vote?], overwhelming thinks so). That moves us to the debate on whether we should do anything it or learn to adapt. I think that reasonable people can disagree on that second question.