Why Macroeconomics as Policy Tool Shouldn’t be Trusted…

…especially of the Paul Krugman strain.

Writes author and University of Rochester professor Steven Landsburg, (bold original)

Supply and demand (and, especially, triangles of welfare loss, etc) are not entirely rigorous, but they’re good useful simplifications that actually give useful (though approximate) answers to important policy questions. Sort of like Ohm’s Law for electrical circuits.

But IS-LM is not like that at all, because IS-LM does not even address the key policy questions in macroecomics. IS-LM can tell you, perhaps, how to fight a recession, but it can’t tell you whether the recession is worth fighting — not even loosely, because the model contains no individual utility functions and no social welfare function. It therefore does not allow you even to formulate the question of whether a given policy is worth its costs, because it provides no framework for weighing costs against benefits.

Analyzing policy via supply and demand is like analyzing electrical circuits with Ohm’s Law. It answers questions, and over a fairly wide range of situations, it answers them with tolerable accuracy. But analyzing policy via IS-LM is like analyzing electrical circuits with a barometer.