Central banks lemmings of quantitative easing

Predictably, the European Central Bank has joined the world's other major monetary authorities in the greatest experiment in the history of central banking. By now, the pattern is all too familiar. First, central banks take the conventional policy rate down to the dreaded "zero bound". Facing continued economic weakness, but having run out of conventional tools, they then embrace the unconventional approach of quantitative easing (QE).

The theory behind this strategy is simple: Unable to cut the price of credit further, central banks shift their focus to expanding its quantity. The implicit argument is that this move from price to quantity adjustments is the functional equivalent of additional monetary policy easing. Thus, even at the zero bound of nominal interest rates, it is argued, central banks still have weapons in their arsenal.

But are those weapons up to the task? For the ECB and the Bank of Japan, both of which are facing formidable downside risks to their economies and aggregate price levels, this is hardly an idle question. For the United States, where the ultimate consequences of QE remain to be seen, the answer is just as consequential.