V. DATA AND ECONOMETRIC ESTIMATION
Prior to estimating the model, we take a quick graphical look at the relationship between
headline inflation and the monetary policy variables (Figure 3). The interest rate we use is the
refinancing rate. Figure 3 suggests a close positive relationship between inflation and growth
in credit to the economy. The relationship between inflation and the nominal interest rate
appears to have changed over time; until 2006 it is hard to see any relationship, but after this
period there seems to be a positive and contemporaneous relationship, which is counterintuitive
at first sight. However, this finding is corroborated by the results of the VAR
simulations discussed below and is not uncommon in the VAR literature, where it is known
as the ‘price puzzle’ (see Sims (1992) and Eichenbaum (1992)). Castelnuovo and Surico
(2006) show that the ‘price puzzle’ can arise when there is high persistence of expected
inflation and the central bank is passive rather than forward-looking in responding to
inflation.