by jpfeifer » Fri Apr 04, 2014 8:40 am
What do you mean with erratic behavior? The described behavior suggests that you have trouble finding the mode.
The problems seem to come from the data treatment. Your model is log-linearized, but you enter the interest rate in levels. That is wrong, because the model implies they are mean zero while the data has a positive mean (it is the real interest rate plus inflation). Please see Pfeifer (2013): "A Guide to Specifying Observation Equations for the Estimation of DSGE Models" on my homepage for details. There, you will also find examples.
Additionally, I suggest you take a look at your data. Plot them. You will immediately see an extreme seasonal pattern in e.g. the growth rate. Hence, some of your data are not seasonally adjusted. You need to fix this before estimation.