Suppose that prior to the recession, I told you that I had a theory of the business cycle. My theory suggested that shocks to net worth were a significant explanation of the business cycle. Following a shock to net worth, consumption, investment, and hours worked would decline. Suppose that I also told you that increases in the monetary base by the Federal Reserve would keep inflation close to the implicit objective, but have little effect on consumption, investment, and real GDP. Given the events of the last four years, this theory seems to fit pretty well with what we have actually observed. What might surprise you, however, is that the framework I am describing is a real business cycle model with financial market frictions. This view seems largely consistent with James Bullard’s interpretation of events.
Suppose instead that I told you that I had the following theory of the business cycle. My theory suggested that liquidity shocks were a significant explanation of the business cycle. Following a shock to liquidity, and without appropriate Federal Reserve policy, nominal and real GDP would decline and unemployment would rise. In addition, suppose that I told you that if the Federal Reserve increased the monetary base without an explicit target or goal that such an expansion would have little effect on real economic activity. Given the events of the last four years, this theory seems to fit pretty well with what we have actually observed. This view is largely consistent with Scott Sumner’s interpretation of events.
I have used these two examples to illustrate a couple of points. First, neither Bullard nor Sumner (or anybody else associated with similar views) are crazy. They have logically consistent ideas that are consistent with casual observation. Second, confirmation bias is dangerous. It is very tempting to have a theory, look at the world, observe events consistent with your theory, and conclude that your theory is correct. But that is just confirmation bias. What is necessary is to provide evidence to support your theory in light of other theories that have observationally equivalent observations. This is substantially harder to do — even for those who realize it is necessary. Third, and perhaps most importantly, the ability to distinguish between these and other competing theories is incredibly important given the vastly different monetary policy implications.