[H]umility is a practical good in the economic-policy debate, because if the effects of economic policies were indisputable and predictable, then there would never be a recession or non-trivial unemployment. But there are recessions and widespread unemployment, which means either that politicians’ ability to manage the economy is much more limited than our political rhetoric suggests (more likely) or that incumbents are intentionally enacting bad policies that they know will produce recessions and unemployment (less likely).
Politicians have obvious incentives to pretend that they have more knowledge and power than they do. Nearly as much damage is done by the priesthood of professional economists and journalists, who for their own narrow interests also exaggerate what politics can achieve, be those interests professional or political or some combination of the two (assuming they can be distinguished).
This lack of humility produces headlines and sound bites like this one on Sunday from The Atlantic: “Tax Cuts Don’t Lead to Economic Growth, a New 65-Year Study Finds.” The piece itself, by business editor Derek Thompson, isn’t terrible, and one has to assume that, like most writers, he probably isn’t responsible for his headlines. But the headlines dominate political discourse, which is by its democratic nature shallow.
In fact, correlating tax-rate changes to growth rates is very close to being meaningless. That’s because the relevant comparison isn’t between observed growth rates under various tax regimes but between observed growth rates and the growth rates that we would have observed under different tax regimes. That more meaningful comparison has the academically and journalistically undesirable quality of being unknowable. Social scientists frequently measure the wrong factor because it is measurable, when the right factor is not.