Over at TNR, I reiterate some of the general points about our lack of knowledge of the actual effects of stimulus that I made here earlier, and show examples of various writers at TNR being all over the place on this question.
I then go on to make a couple of general points about what I believe this ignorance implies for how we should make public policy:
First, we should treat anybody who states definitively that the result of stimulus policy X will be economic outcome Y with extreme skepticism. And weaseling about the magnitude of the predicted impact such that all outcomes within the purported range of uncertainty still magically lead to the same policy conclusion doesn’t count; we should recognize that we don’t even know at the most basic level whether stimulus works or not.
Second, “boldness” in the face of ignorance should not be seen in heroic terms. It is a desperate move taken only when other options are exhausted, and with our eyes open to the fact that we are taking a wild risk. Actual science can allow us to act on counterintuitive predictions with confidence—who would think intuitively that it’s a smart idea to get into a heavy metal tube and then go 30,000 feet up into the air? But we don’t have this kind of knowledge about a stimulus policy. We are walking into a casino and putting $800 billion dollars down on a single bet in a game where we don’t even know the rules. In general, in the face of this kind of uncertainty, we ought to seek policy interventions that are as narrowly targeted as is consistent with addressing the problem; tested prior to implementation to whatever extent possible; hedged on multiple dimensions; and designed to be as reversible as is practicable.