My good friend and sometime mentor, Brian Wesbury, argues that the natural rate of interest is the same as the nominal GDP growth rate.

FORBES: What Is the Liquidity Premium? What Does It Mean?

As US unemployment continues to head south towards its natural rate, and the prospect of an interest rate spike is a possibility, there is one factor that may avert, or at least moderate, an interest rate spike: The yen tsunami, i.e.

FORBES: What May Keep US Interest Rates From Spiking

Inflation reflects itself first in a lowering of the actual rate of interest beneath the natural rate.

FORBES: Why Interest Rates Tell Lies About Inflation, Growth And Just About Everything Else

Even the most hawkish members of the Fed's interest-rate setting committee believe that the U.S. natural unemployment rate is below 6.5%.

WSJ: Wonk Wars: How Big Are EU Deficits?