A monetary regime change has occurred that has lowered the growth rate and growth path of nominal demand. Since the recovery started in 2009Q3, NGDP growth has averaged 3.4 percent. This is below the 5.4 percent of 1990-2007 period (blue line in the figure below) or a 5.7 percent for the entire Great Moderation period of 1985-2007. Macroeconomic policy has dialed back the trend growth of nominal spending by 2 percentage points. That is a relatively large decline. This first development can be seen in the figure below.

The figure above also speaks to the second part of this regime change: aggregate demand growth was not allowed to bounce back at a higher growth rate during the recovery like it has in past recessions. Historically, Fed policy allowed aggregate demand to run a bit hot after a recession before settling it back down to its trend growth rate. This kept the growth path of NGDP stable. You can see this if the figure above by noting how the growth rate (black line) typically would temporarily go above the trend (red line) after a recession.

Had macroeconomic policy allowed aggregate demand growth to follow its typical bounce-back pattern after a recession, we would have seen something like the blue line in the figure. This line is a dynamic forecast from a simple autoregressive model based on the Great Moderation period. This naive forecast shows one would have expected NGDP growth to have reached as much as 8 percent during the recovery before settling back down to its average. Instead we barely got over 3 percent growth. This is why NGDP has never caught back up to its pre-crisis trend path.

Again, these two developments are, in my view, the real story behind the drop in trend inflation. And to be clear, I think both the Fed's unwillingness to allow temporary overshooting and the safe asset shortage problem have contributed to it.

I went on to say this is the monetary regime change no one asked for. It is also one that many observers seem to miss in their analysis of Fed policy since the crisis.

Well, I was on twitter discussing long-term treasury yields and monetary policy with Tim Duy and Joel Wertheimer. I decided to whip up some charts comparing 1-year head NGDP forecasts from the Philadelphia Fed's Survey of Professional Forecasters against 10-year treasury yields. The results, in my view, are consistent with the claim that there was a monetary regime change in 2008.

First, here is the chart for the 1980:Q1-2007:Q4 period. It shows a fairly strong relationship between expected NGDP growth and long-term treasury yields:

The next figure shows the relationship for the period since 2008:Q1. Say goodbye to that relationship:

Just to be robust, I took out the outliers in the above chart (which are for the periods 2008:Q4-2009:Q2) and got the following chart:

So something has changed in the relationship between expected NGDP growth and long-term treasury yields. The monetary regime change story outlined above coincides closely with this breakdown. Here is one way to connect these two developments. Before 2008 the Fed allowed its tightening to follow the pace of recovery, whereas afterwards the Fed has tended to get ahead of the recovery in its desired and actual rate hikes. If so, the Fed's tightening post-2008 would have slowed down the recovery and lowered the expected future path of short-term interest rates. This overreacting by the Fed would have kept long-term interest rates from rising with expected rises in NGDP growth. This type of behavior would also be consistent with a monetary regime change where only low rates of NGDP growth and inflation are tolerated. This is what appears to have happened in 2008.