The Fed has taken many actions over the past 30 years, using a model that
assumes tight relationships between short interest rates and inflation / labor unemployment.
That uncertainty can be broken down into 2 pieces: statements based on model weighting ignore uncertainty about how
tight (and real) the constraint actually is, while statements based on an
assumed functional
relationship not only neglect uncertainty related to constraint validity, but also ignore uncertainty regarding what the correct functional
relationship should actually be.